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Facile microwave synthesis of carbon dots powder with enhanced solid-state fluorescence and its applications in rapid fingerprints detection and white-light-emitting diodes
Abstract
In this report, we successfully developed a simple and fast MW-assisted method for preparing CDs with strong solid-state fluorescence (SSF) by using phthalic acid and piperazine as precursors. The prepared p-CDs can be obtained in high yield (48.7%) and emit bright yellow-green SSF under 365 nm UV light. The absolute PL quantum yield (PLQY) of p-CDs in solid state was measured to be 20.5%, which is much higher than that in aqueous solution. This interesting phenomenon shows that p-CDs not only successfully conquer the aggregation-caused fluorescence quenching (ACQ) effect, but also achieve enhanced fluorescence emission, which was rarely reported in previous literatures as CDs in solid state always reduce their fluorescence emission due to the excessive resonance energy transfer (RET) or direct π-π interactions. In addition, the relationship between the feed ratio of precursors and optical properties of the CDs were also investigated detailedly. Based on their strong SSF, the p-CDs were successfully used in rapid latent fingerprints detection and white light-emitting diodes (WLEDs) preparation with high quality. In summary, this research not only developed a new type of CDs with strong enhanced SSF, but also offered a valuable reference for design SSF-emitting CDs with high yield.
... C-dots have a propensity to self-quench in their solid form [35]. There have been numerous attempts to mitigate this negative effect, including the use of diluent matrix structures [36,37], the creation of core-shell small structures [38], the incorporation of heteroatom doping [39,40], the utilization of Resonance Energy Transfer (RET) and -interactions [41], the application of molecular gaps [42], and other methods. ...
... Wang and others, [41] with the aid of a microwave, piperazine and phthalic acid were pyrolyzed to create graphitic C-dots (pC-dots), which have an average size of 1.5 nm. The pC-dots possess a QY of 20.5% in a solid state and show a very bright yellowgreen color beneath 365 nm light. ...
Carbon dots have received a lot of interest because to their outstanding fluorescence capabilities, low cost of production, and non-toxic qualities. This analysis dives into current developments in fields such as criminal justice, forensic toxicology, and anti-counterfeiting methods. Because of their color-tunable actions in response to incident radiation, C-dot-based combinations have proven particularly beneficial for improving latent fingerprints, providing superior contrast against different backgrounds. As optical nano probes, these dots demonstrate amazing sensitivity and selectivity, allowing for the exact detection of diverse substances such as biological molecules, pharmaceuticals, weapons of mass destruction, heavy metals, and hazardous chemicals. C-dots may be effortlessly incorporated into ink and polymeric formulation due to their adaptive structural and chemical properties, ushering in a revolutionary era of inexpensive barcode as well as nano tags for objects to be identified and anti-counterfeit applications. To assure significant societal and economic benefits, the transition from these promising research discoveries into effective advances requires a coordinated strategy comprising materials researchers, biologists, legal professionals, and digital engineers.
... The key to the ability of graphene-based compositions to recover fingerprints is their capacity to change color when exposed to various light sources, allowing background-free photos and maximizing the accuracy of fingerprint analysis. The use of a diluent matrix, the creation of core-shell nanostructures, the incorporation of heteroatom doping, the utilization of effects, such as resonance energy transfer and interactions, the use of molecular spacers, and other techniques have been suggested to combat the tendency of graphene or other carbon-based nanomaterials in the solid state for self-quenching [13,14]. Fernandes et al. were the first to demonstrate the use of carbon nanomaterial-based powders for fluorescent visualization of dormant finger impressions. ...
... Similar to the current research, Nugroho et al. [28] developed graphene/carbon dots from Magnolia grandiflora at various times (14,16,18, and 20 min) and further surfacefunctionalized with hydrogen sulfide (H 2 S) to synthesize S-doped carbon quantum dots (CQDs). The synthesized S-doped CQDs had a uniform size, according to TEM analysis, along with an amorphous structure and water solubility, and also contained hydroxyl and carboxyl groups, excitation light-dependent characteristics, and high photostability. ...
In recent years, the application of biocompatible and non-toxic nanomaterials for the detection of fingerprints has become the major interest in the forensic sector and crime investigation. In this study, waste chickpea seeds, as a natural resource, were bioprocessed and utilized for the synthesis of non-toxic graphene nano-sheets (GNSs) with high fluorescence. The graphene GNS were synthesized via pyrolysis at high temperatures and were characterized by TEM, XPS, fluorescence and UV-Vis spectroscopy, and FTIR analysis. The GNS exhibited excitation-independent emission at about 620 nm with a quantum yield of over 10% and showed more distinct blue light under a UV lamp. Biocompatibility of the synthesized GNS in terms of cell viability (88.28% and 74.19%) was observed even at high concentrations (50 and 100 mg/mL), respectively. In addition, the antimicrobial properties of the synthesized GNS-based coatings were tested with the pathogenic strain of Bacillus cereus via live/dead cell counts and a plate counting method confirming their biocompatible and antimicrobial nature for their potential use in safe fingerprint detection. The developed chickpea-originated fluorescent GNS-based spray coatings were tested on different surfaces, including plastic, glass, silicon, steel, and soft plastic for the detection of crime scene fingerprints. Results confirmed that GNS can be used for the detection of latent fingerprints on multiple non-porous surfaces and were easy to detect under a UV lamp at 395 nm. These findings reinforce the suggestion that the developed fluorescent GNS spray coating has a high potential to increase sensitive and stable crime traces for forensic latent fingerprint detection on nonporous surface material. Capitalizing on their color-tunable behavior, the developed chickpea-originated fluorescent GNS-based spray coating is ideal for the visual enhancement of latent fingerprints.
... An extensive examination was additionally undertaken to determine the correlation between the precursor feed ratio and the optical characteristics of the CDs. The utilization of p-CDs for the expeditious identification of latent fingerprints and the fabrication of superior white light-emitting diodes (WLEDs) was a resounding success [62]. ...
The convergence of nanotechnology and forensic science presents a transformative era for criminal investigations. This review article explores how a diverse range of nanomaterials, including carbon-based nanomaterials (like graphene oxide and fluorescent carbon dots), metallic nanoparticles, and polymeric nanofibers, are revolutionizing various forensic disciplines. From the superior performance and non-toxic nature of graphene oxide in latent fingerprint detection to the rapid cocaine analysis enabled by 3D-printed electrodes, nanotechnology is pushing the boundaries of forensic capabilities. Its applications extend beyond these examples, with nanocomposites comprised of various nanomaterials offering practical solutions for heavy metal extraction in environmental forensics. Trace evidence analysis is experiencing a boost through the use of different nanomaterials, including fluorescent carbon dots, enabling enhanced visualization and targeted detection. Furthermore, high-throughput nanotechnology platforms are addressing limitations in DNA sequencing, paving the way for faster and more cost-effective genetic analysis. Even document examination stands to benefit from non-destructive nanoscale sensors, preserving the integrity of evidence. However, integrating nanotechnology into forensic science necessitates navigating regulatory and environmental hurdles, while upholding ethical and procedural standards. This review delves into these advancements, highlighting the anticipated trajectory of nanotechnology in forensics and the ethical considerations that must be addressed for its successful implementation.
Graphical Abstract
... Additionally, the consistent heating process provided by microwave radiation leads to more homogeneous and well-controlled particle size and composition compared to other methods. 24,25 The properties of CQDs can also be tailored by controlling the synthesis conditions and the doping agent used, making them suitable for various applications, including bioimaging, 10,26−29 photovoltaics, 18,30,31 and sensing. 11,32 Toxic heavy metal ions pose a significant threat to the environment, human health, and animal health. ...
n this study, carbon quantum dots (CQDs), which were
synthesized from arabica coffee ground-derived activated carbon, have been
successfully employed as a fluorescence sensor to detect Fe3+ ions. CQDs were
fabricated using microwave heating for 5−10 min, which emitted vibrant blue
light at 455 nm when exposed to excitation at 365 nm. Dynamic light scattering
(DLS) analysis revealed that the average size of CQDs was 10.12 nm with a
quantum yield of 6.01%. Fluorescence detection was developed for sensing Fe3+,
Pb2+, and Cr3+ ions. The addition of the three metal ions resulted in a decrease
in the fluorescence (FL) intensity of the CQDs, with the addition of Fe3+ ions
demonstrating a more significant decrease in FL compared to the addition of
both Cr3+ and Pb2+ ions. The results indicated that the CQDs synthesized from
activated carbon of arabica coffee waste performed as a selective fluorescent
detector for Fe3+ ions, with a detection limit of 0.27 μM
... et, stainless steel, polypropylene film, and carnelian and observed under the 365-nm wavelength which gives the blue fluorescence.Xu et al. (2014) fabricated and used silica-based N-doped CD's (CD-25) to develop latent fingermarks on filter paper. The developed CD's are non-toxic and produce yellowish green fluorescence in aqueous and solid states.Wang et al. (2019) developed and used solid-state fluorescent CD's (CD-26) to develop latent fingermarks on glass, tin foil, plastic, weighing paper, coin, desk, and reagent bottle cap. The use of CD-26 was suggested as an excellent fluorescent coloring reagent for the rapid ...
Background
Fingermarks are one of the oldest, reliable, and universally accepted evidence found on the crime scene. They can be used to link suspect with scene of crime and weapon of offence. Fingermarks are frequently used to investigate criminal cases and identify missing persons and criminals.
Main text
Conventional methods such as cyanoacrylate fuming, iodine fuming, ninhydrin, silver nitrate, small particle reagent, and powder dusting are routinely used to detect and develop latent fingermarks on various surfaces of forensic importance. However, these methods suffer several limitations including poor contrast, low sensitivity, background interference, and low specificity. To overcome these limitations, nowadays, nanoparticles have gained importance in the development of latent fingermarks. In this review, we focus on the carbon dots (CD's) nanomaterial for the development of latent fingermarks. CD’s have superior fluorescence performance, color tuneability, and low synthesis cost and are non-toxic. The color and intensity of luminescence of CD's depend on its morphology and synthesis method. CD's can be used either in solid or solution form to develop latent fingermarks on the various porous and nonporous surfaces.
Conclusion
CD’s are potentially a good candidate to develop latent fingermarks on wide range of porous and nonporous items of forensic importance. The fingerprints developed with CD’s show excellent contrast and resolution. Their small size, biocompatibility, facile and low-cost synthesis, and color tuneability can be successfully utilized to overcome the limitations of the conventional methods.
... These properties of CQDs make it a promising candidate for applying in cellular imaging, biosensing, drug delivery and catalysis (Li et al 2012). Nanomaterials of carbon can be synthesized in many shapes, the known among them are: graphene, carbon nanotube (CNTs), which could be multi or single-walled nanodiamonds, Nanofibers, Buckminsterfullerene (C60) (Li et al 2011, Li et al 2012, Rochester 2013, Pires et al 2015, Dao et al 2016, Thambiraj andShankaran 2016), comprising graphitic layered sheets and, the recently developed Carbon Dots (CQDs) (Li et al 2012, Jusuf et al 2018, Dhiman and Singh 2019, Wang et al 2019, Zhou et al 2019, Anand et al 2020. All of these carbon nanomaterials show excellent physicochemical properties, possibly evolving the technology in the near future (Li et al 2011). ...
The scarcity of fresh air, drinking water, and soil is a matter of serious concern worldwide owing to the presence of organic pollutants in the environment. The organic dye, such as methylene blue (MB) has enormous toxic effects on the environment and human health. Therefore, the degradation of non-biodegradable dyes is very important to reduce toxicity in water and-a step towards waste water management systems. This paper focuses on the degradation of non-biodegradable MB dye using carbon quantum dots (CQDs). CQDs were synthesized by microwave irradiation method using citric acid and L-cysteine as precursor and it was further confirmed by X-ray Diffraction (XRD), Raman Spectrum, Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray (EDX) spectroscopy techniques. The optical properties of the synthesized CQDs of 8 nm, were investigated by UV-visible spectroscopy technique and the absorption peak appeared at 340 nm which corresponding to n → π* transition. In photoluminescence (PL) spectra analysis, the highest emission peak was obtained at 440 nm when excited at 345 nm. The synthesized CQDs were used for the dye degradation of MB in distilled water and degradation percentage was calculated and found to be 99.17 % in 90 minutes under UV light irradiation. Also, studied the impact of degraded water in seed germination of Cicer arietinum (black gramme) and calculated the seed germination growth rate in degraded water was found to be 15-20 % more than the seed germination growth rate in MB containing dye water.
... * Yuqing Liu 48132269@qq.com Wang et al. 2019). However, because of the wide application of CQDs, they will inevitably enter the environment during the production, application, disposal and recycling. ...
As luminescent nanomaterials, the carbon quantum dots (CQDs) research focused on emerging applications since their discovery. However, their toxicological effects on the natural environment are still unclear. The freshwater planarian Dugesia japonica is distributed extensively in aquatic ecosystems and can regenerate a new brain in 5 days after amputation. Therefore it can be used as a new model organism in the field of neuroregeneration toxicology. In our study, D. japonica was cut and incubated in medium treated with CQDs. The results showed that the injured planarian lost the neuronal ability of brain regeneration after treatment with CQDs. Its Hh signalling system was interfered with at Day 5, and all cultured pieces died on or before Day 10 due to head lysis. Our work reveals that CQDs might affect the nerve regeneration of freshwater planarians via the Hh signalling pathway. The results of this study improve our understanding of CQD neuronal development toxicology and can aid in the development of warning systems for aquatic ecosystem damage.
... The fingerprint patterns and second-level details, such as the ridge termination and bifurcation, were clearly observed with high quality under UV light (365 nm). In a similar way, H.-J. Wang et al. (2019) have prepared CDs from phthalic acid and piperazine and observed excellent results for the latent fingerprint development in several surfaces and common objects, such as desk, bottle cap and coin. ...
The majority of conventional techniques for latent fingerprint enhancement are based on chemical reactions or interactions between the developer and fingermark residue components, providing contrast between the surface and the fingerprint ridges. However, these methods might be limited by factors associated with particle size, toxicity of the reagent, selectivity, or sensitivity, that may be circumvented by the synthetic design of innovative materials based on nanoparticles or macromolecular materials, such as conducting polymers, applied as latent fingerprint developers on different surfaces and conditions. Since the structural, optical and electronic properties of the material can be tailored by its molecular scale, the size control of the developer plays an important role to improve the interaction with the latent fingermark residue and/or the surface, enhancing the color contrast and the quality of the developed image (or dactylogram). Hence, creating new reagents and strategies to apply nano‐ and macromolecular scale materials as latent fingermark developers constitutes an exciting rapidly expanding area, generating a wealth of new materials that lead to forensic methodologies with enhanced performance. Recent progress in the application of such materials for development of latent fingermarks present on different surfaces and subject to complex circumstances will be discussed. This will focus on the main barriers to making nanoparticles and conducting polymers viable—and occasionally preferred—materials routinely used by forensic experts, and the potential advantages over conventional methodologies in the acquisition and analysis of crime scene evidence.
This article is categorized under: Forensic Chemistry and Trace Evidence > Trace Evidence
Forensic Chemistry and Trace Evidence > Fingermarks and Other Marks
Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods
... The basic principle for CD-based materials for fingerprint retrieval is based on the fact that they accept different colors when irradiated by various light sources, permit contextual free images, and increase the consistency of fingerprint study. Whereas CDs in the solid state have a propensity to self-quenching [24], a number of approaches have been projected to overwhelmed this result, comprising the use of a diluent [25,26], design of coreÀshell nanostructures, heteroatom doping [27,28], exploitation of special effects like πÀπ interactions and resonance energy transfer [29] and the molecular spacers [30]. ...
Fluorescent carbon dots (CDs) with stable physicochemical properties are one of the fascinating classes of carbon nanomaterials that have small particle size and distinctive optical properties added widespread attention in recent years. Along with the unique optical properties such as high photoluminescence, photo-bleaching resistance, and light stability, CDs have the promising advantages of low cost, good biocompatibility, environmental friendliness, and easy functionalization. Moreover, CDs can surface passivation and functionalization with other types of materials to get the nanostructured composites with outstanding properties, which offer new visions and concepts for the research of several fields. Hence, CDs are promising nanomaterials for chemical sensing, biological imaging, nanomedicine, photocatalysis, adsorption treatment, and electrocatalysis. This chapter details contribution of CDs in forensic, security, and other related analytical applications. It is likely to offer a significant guidance for the further study of CDs in the field of forensic science and detection.
... [23][24][25][26][27] Multiple peaks observed in XRD are impurity peaks due to incomplete carbonization of plastic waste. 28 Most of the CDs reported in literature show spherical nano particle morphology based on TEM and HRTEM images with graphitic crystal structure based on XRD data [29][30][31][32][33] and our data match with the ones reported. Further, quality of graphitic structure in fabricated plastic CDs is explored using Raman spectra (Fig. 2d). ...
The Covid-19 pandemic has generated a lot of non-degradable biohazardous plastic waste across the globe in the form of disposable surgical and N95 masks, gloves, face shields, syringes, bottles and plastic storage containers. In the present work we address this problem by recycling plastic waste to single system white light emitting carbon dots (CDs) using a pyrolytic method. The synthesized CDs have been embedded into a transparent polymer to form a carbon dot phosphor. This CD phosphor has a broad emission bandwidth of 205 nm and is stable against photo degradation for about a year. A white LED with CRI $70 and CIE coordinates of (0.25, 0.32) using the fabricated CD phosphor is reported. Further our phosphor is scalable and is environmentally sustainable, and will find wide application in next generation artificial lighting systems.
... A variety of efforts to develop rapid, sensitive, and economical techniques for the detection of latent fingerprints have emerged in the past few years [1]. To date, these techniques including powder dusting [7][8][9][10][11], fluorescent dye staining [12,13], ninhydrin spraying [14], cyanoacrylate/ iodine fuming [1,15], vacuum metal deposition, and small particle reagent method [16][17][18][19][20] are the most widely used due to their simplicity, efficiency, and ease of operation. Although these traditional methods are effective under ordinary circumstances, there are still numerous challenges to visualize latent fingerprints with high contrast and low background interference on multicolor background, and there is an urgent need in seeking simple and efficient methods for developing the latent fingerprints with improved contrast, sensitivity, and selectivity. ...
This article explored the application of novel organic-inorganic hybrid polystyrene nanoparticles (PSNPs) with trichromatic luminescence for the detection of latent fingerprints. The PSNPs were synthesized by encapsulated Eu(DBM)3phen, coumarin 6, and FDBT into the polystyrene nanoparticles through the swelling method and applied them to visualize latent fingerprints. The PSNPs had a spherical morphology with an average diameter of 310.7 nm, and they emitted trichromatic fluorescence (525 nm/570 nm/610 nm) under 365 nm excitation wavelength with green/yellow/red color under filters. They were less likely to aggregate, float or stain the background when treating fingerprints. The developed fingerprints with excellent clarity of ridges and contrast could be viewed, and the digital magnification of fluorescence-developed fingerprints provided more minutiae details about some regional patterns. The colorimetric and fluorescent trichromatic light could provide complementary signals without the background interference from fluorescent substrates and/or complex multicolor surfaces, which improved the applicability of fluorescent nanoparticles for fingerprints development. PSNPs are promising for the detection of latent fingerprints and practical criminal investigations with their ease of operation, eco-friendly properties, and excellent trichromatic optical performance.
... The phenomenon is called quenching, when the molecules at higher energy are deactivated and the fluorescence ceases. (8). Synthesizing of carbon dots can be done easily and is a hydrothermal process (microwaveassisted method). ...
Nanotechnology is brightest future of science and rapidly emerging in every
filed of science such as Medicine, Physics, Chemistry, Pharmacy, molecular medicine
and even in forensic science. This field already developed various nanomaterials for with
biomedical and analytical fields and forensic fingerprinting. Carbon dots are such
developed materials which have great biocompatibility, fluorescence properties,
inertness, photo-bleaching
resistance, low toxicity
withcosteffectiveandenvironmentalfriendlyandhaspotentialapplicationinlatentfingerprint
development.Carbondotscanbesynthesizedbyeasyprocesseswithchemicalusingcitricacid
L-glutathione,thiourea,eggwhites,coffeegrounds,egg whites, applejuice,aspirin,andeven
from chocolate. Various color of carbon dot can be produced by specific chemical
reactions. The majority are red, green, blue and yellow color emission type under
different excitation light frequencies and used in both method as spray and powder form.
Carbon dots method are rapid and easy to perform, latent print can be developed from
water soaked evidence and can be preserved for very long time. Latent prints can be
developed form porous, non-porous and semi-porous substrates, which have potential to
show
primary, secondary and tertiary details
forfingerprintevenafteraprolongageingupto60days.Developedprintcanbeseenbynaked eye
and photographed by digital camera under UV light. Hence. Carbon dots have wide
application and potential to develop any kind of latent prints and can be used in daily
routing of crime scenesearch
Green fluorescent curcumin-doped cellulose nanocrystals obtained by anchoring curcumin on cellulose nanocrystals exhibit better performances for detecting high-level features of ridges of fresh and non-fresh latent fingerprints on various substrates.
The synthesis of eco-friendly carbon quantum dots (PCQDs) from Pistachio shells is a straightforward process with versatile applications. These PCQDs, derived from non-toxic sources, are generated through a hydrothermal method and have garnered significant attention due to their outstanding properties. While there are many advanced CQDs available, the full potential of PCQDs remains untapped. These PCQDs, with their exceptional optical characteristics, serve as highly sensitive nano-probes for fluorometrically measuring Cu2+ ions. The fluorescence (FL) intensity of these nano-probes shows a linear correlation with Cu2+ ion concentration in the range of 0 to 4 µM, boasting a low detection limit of around 0.351 µM. This sensitivity is achieved through resonance energy and electron transfer-induced FL quenching. Importantly, carbon dots from Pistachio shells can be used as ink-free patterned substrates, making them ideal for printing and non-destructive collection and detection of latent fingerprints (LFPs). The LFPs can be developed using a simple powder dusting method with PCQDs and are visible under 365 nm UV light. This technique allows for lifting and identifying long-term exposed LFPs from various surfaces without causing any damage. Additionally, extensive research has been conducted on various pore properties such as size, shape, number, position, type, and inter-distance. Mathematical modelling implemented in Python-based software was used to investigate single fingerprints and two overlapped fingerprints. Furthermore, a transparent anti-counterfeiting (AC) film is fabricated using PCQDs and polyvinyl alcohol (PVA), offering effective AC capabilities through their green emission under 365 nm UV light. Notably, these PCQDs exhibit sustainability, exceptional flexibility, and foldability, expanding their potential applications in flexible display devices, dermatoglyphics and data encryption. The overall results clearly demonstrate that PCQDs are a highly efficient luminescent platform with a wide range of applications.
Novel cellulose-based composites were developed by integrating the rhodamine B (RhB) with cellulose microparticles and used to detect latent fingerprints (LFPs). The cellulose-based composites containing the various contents of RhB (5.4, 9.7, and 19.6 mg g⁻¹) with good luminescence were obtained by simple adsorption method. Under 365 nm light irradiation, cellulose-based composite can produce the bright red fluorescence in solid-state. The images of the LFPs on the surface of the substrates with variable textures and colors can be detected with integral ridge patterns and finely clear detail characteristics in level 2 (such as scar, core, island, bifurcation and termination) and level 3 (such as sweat holes and line shape). The fresh and aging LFPs can be finely detected by the cellulose-based composite with the little interference of background because the red-emissive can efficiently avoid the interference from self-fluorescence of the substrates. These results suggested that the cellulose-based composite with favorable applicability and dependability could be a promising candidate for the visualization of the LFPs.
Nanotechnology is a flourishing branch of research due to the incredible properties nanomaterials exhibit over their massive counterparts. Carbon nanodots are the members of the carbon nanoparticle family with prominent properties like hydrophilicity, low toxicity, biocompatibility, increased stability and ease of functionalization. They are excellent replacement to metal based quantum dots which are highly toxic. Carbon nanodots are being used in the fields of medicine, environmental science, drug delivery and forensic science. Applications of carbon nanodots can be seen in bio imaging, bio sensing, cancer diagnosis and treatment, biological activities, solar cells and as photo catalysts. Forensic science is the science behind crime investigation and evidence analysis. Development of novel, rapid, on site testing materials for accurate, specific and sensitive detection of forensic evidences is required for delivery of justice to the victims of crime. Carbon nanodots have shown promising applications in the field of forensic science as well. Use of carbon nanodots as invisible ink for anti-counterfeiting application of currency and security documents and use of these nanomaterials in development of latent fingerprints are some forensic applications. Carbon nanodots based detection of food contaminants, heavy metal poisons, pesticides, illicit drugs and explosives are other forensic applications. Carbon nanodots are showing a future direction in development of on field testing kits for forensic evidences.
Developing novel waste recycling strategies has become a feasible solution to overcome environmental pollution. In this work, a method of using waste wind turbine blade (WTB) as a carbon source to synthesize blue fluorescent carbon dots (B‐CDs) by hydrothermal treatment is proposed. B‐CDs are spherical and have an average particle size of 5.2 nm. The surface is rich in C–O, C=O, −CH 3 , and N–H bond functional groups, containing five elements: C, O, N, Si, and Ca. The optimal emission wavelength of B‐CDs is 463 nm, corresponding to an excitation wavelength of 380 nm. Notably, a relatively high quantum yield of 29.9% and a utilization rate of 40% were obtained. In addition, B‐CDs can serve as a photocatalyst to degrade methylene blue dye, with a degradation efficiency of 64% under 40‐min irradiation conditions. The presence of holes has a significant influence on the degradation process.
Highly green emissive solid‐state carbon dots (CDs) with photoluminescence quantum efficiency of 58% are prepared through a rapid microwave assisted heating method. Due to the spatial confinement from the biuret crystal matrix, aggregation among CDs is effectively suppressed, thus allowing the CDs to give efficient emission in the solid‐state. The CDs show excitation independent emission and mono‐exponential decay characteristics with a nearly constant lifetime of ≈13 ns upon varying the detected emissions, indicating the presence of a single type of emissive state in the CDs. Due to their high quantum efficiency and short lifetime, the obtained CDs are applied as the color conversion layer of a near‐ultraviolet micro light‐emitting diode (µLED) chip (405 nm) for visible light communication, achieving a modulation bandwidth of 165 MHz, which is much higher than the bandwidth of the conventional combination of Ce³⁺‐doped yttrium aluminum garnet phosphor with GaN LED. Moreover, the green emitting solid‐state CDs are applied to fabricate a prototype white LED device, which exhibits good lighting suitability with a color rendering index of 90.6 and a Commission Internationale de L'Eclairage chromaticity coordinates of (0.327, 0.332).
Novel cellulose-based composites by integrating the rhodamine B (RhB) with cellulose microparticles are developed and used to detect latent fingerprints (LFPs). The cellulose-based composites containing the various amounts of RhB (5.4 ± 0.2, 9.7 ± 0.3, and 19.6 ± 0.3 mg g − 1 ) with the good photostability are obtained by simple adsorption method. Under 365 nm light irradiation, cellulose-based composite can produce the bright red fluorescence in solid-state. The images of the LFPs on the surface of the substrates with variable textures and colors are detected with integral ridge patterns and finely clear detail characteristics in level 2 and 3. The fresh and aging LFPs can be finely detected by the cellulose-based composite with the little interference of background because the red-emissive can efficiently avoid the interference from self-fluorescence of the substrates. These results suggest that the cellulose-based composite with favorable applicability and dependability can be a promising candidate for the visualization of the LFPs.
A convenient and mild preparation of multicolor carbon dots (CDs) was achieved using solvothermal process and extraction. After CDs as the cross-linking agent was doped into γ-(2,3-epoxypropoxy)propytrimethoxysilane solution, orange, yellow,...
Preparation of GQDs for application in cell imaging.
Recently, carbon dots (CDs) have gained much attention in optoelectronic fields on account of their superior optical and environmentally friendly properties. Nevertheless, aggregation-induced quenching (AIQ) effect of solid-state CDs and thermal quenching caused by high temperatures severely hinders their further development. Herein, a novel wCDs/BNNS-OH hybrid nanostructure was synthesized by combining blue CDs (bCDs) and yellow CDs (yCDs) to the hydroxylated boron nitride nanosheets (BNNS–OH) surface. The uniform dispersion of CDs in BNNS-OH effectively alleviates the undesirable AIQ effect, and enables CDs/BNNS-OH composites to have color-tunable fluorescence characteristics. The wCDs/BNNS-OH/PVA composite film was obtained by encapsulating wCDs/BNNS-OH into polyvinyl alcohol (PVA). The film exhibits excellent luminescence stability in the air, ultraviolet light, water, and high-temperature environment. Meanwhile, since wCDs/BNNS-OH establishes an effective heat transfer channel in the PVA matrix, the working temperature of CDs in the wCDs/BNNS-OH/PVA film is greatly reduced. Moreover, the prepared wCDs/BNNS-OH/PVA film is flexible enough to retain the photoluminescence intensity unchanged after thousands of bending cycles. This high stability and heat dissipation wCDs/BNNS-OH/PVA composite film will facilitate the application of CDs in flexible and foldable lighting devices.
This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow–green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.
Fluorescent nitrogen-doped carbon dots (FNCDs) were prepared from the fruits of Annona squamosa by hydrothermal method, further they were characterized and studied for the reduction of Reactive Red-120 (RR-120) dye and bio-imaging. Functional groups, surface functionalities present in FNCDs and as well as nitrogen doping were studied using FT-IR and XPS techniques. The optical properties of FNCDs were assessed using UV–Visible and PL spectroscopy. The quantum yield of FNCDs was 14.16%. HR-TEM results revealed the spherical nature of FNCDs with 4 ± 0.25 nm in size and AFM data revealed the height of FNCDs. The amorphous nature of FNCDs was confirmed from the results of XRD, Raman spectra and SAED patterns. TGA data brought out the thermal behavior of FNCDs. These FNCDs were tested for their catalytic role in the reduction of RR-120 dye by NaBH4. Results showed that FNCDs could catalyze the reduction of RR-120 dye within 12 min and the reduction products were analyzed using mass spectral data. The reduction reaction was explained on the basis of the Langmuir-Hinshelwood mechanism. The possible use of FNCDs as fluorescent probes in cell imaging was also explored by MTT assay.
Exploiting the intelligent stimuli-responsive fluorescent materials, which can selectively recognize lysozyme in fingerprints and enable high-contrast imaging, is still a challenge in latent fingerprints (LFPs) detection. Herein, based on Fluorescence Resonance Energy Transfer (FRET) mechanism, aptamer functionalization and high-contrast reversible dual-color photoswitching fluorescence of polymeric nanoparticles (LBA-RPFPNs) have been successfully constructed for efficient imaging of LFPs. Experiments results showed that LBA-RPFPNs displayed good water dispersibility, fast photo-responsiveness, favorable photoreversibility and good long-term stability. Of note, the aptamer possessed the ability of LBA-RPFPNs to target lysozyme in LFPs, thus realizing the selectivity of LFPs. Furthermore, the fluorescence of LBA-RPFPNs was reversibly switched between green and red through UV/visible light, achieving for high-contrast imaging of LFPs. This strategy provides good potential in disclosing the valuable information within LFPs.
The quest for the design and synthesis of carbon dots with anti-counterfeit properties that are derived via green, environmentally friendly and economical procedures is a continuous process. Carbon dots (C-dots) derived from biowaste are cheap to synthesize, possess good photo-stabilityand high synthetic yield, making them applicable in the anti-counterfeiting of currency. Herein, we report a novel eco-friendly, cheaper, and faster method for the synthesis of carbon dots with strong photoluminescence properties from monkey orange fruit (Strychnos spinosa) biowaste. The presence of the hydroxyl and carbonyl functional groups of the carbon dots were determined by the Fourier transform infrared spectroscopy (FTIR). The carbon dots showed strong blue emission fuorescence (emission wavelength of 452 nm) when excited at 330 nm. The morphology and size were determined by the atomic force microscopy (AFM) which indicated amorphous and
spherical nanoparticles with an average size of less than 2 nm. The no-crystallinity of the asprepared carbon dots was con¯rmed using X-ray diffraction which showed the graphite-like structure. The carbon dots were produced and demonstrated good photo and chemical stability as well as high covert properties. The anti-counterfeiting of currency application by the synthesized carbon dots was demonstrated when the subsequent gel ink printed on the currency showed excellent chemical stability when exposed to washing with water, ethanol, and acetone. It also showed superior photostability when exposed to UV light at 365 nm and daylight for an extended period of up to 6 h. This work provides a facile, economical, and green approach for large scale production of carbon dots from the abundant biowaste.
Latent fingerprints (LFPs) powders play a crucial part in the detection of LFPs by powder-dusting methods in forensic sciences, due to the facile, onsite, and easy-to-operate properties. However, conventional LFPs powders suffer from some drawbacks, such as high toxicity, low contrast, sensitivity and selectivity. Herein, a novel fluorescent composite powder was synthesized and used for the detection of LFPs. The resultant composite powder shows an enhanced fluorescence due to the protection of the emission of fluorescent carbonized nanoparticles (FCNPs) from being quenched in the solid state. Subsequently, the fluorescent composite powder was successfully applied to detect LFPs on various substrates. This work provides a promising strategy for developing FCNPs-based fluorescent powders for the detection of LFPs in forensic science.
Latent fingerprint detection and visualization remains a challenge especially where problems of poor contrast, auto-fluorescent surfaces and patterned backgrounds are encountered. As a result there is an increasing interest in the development of simple, cost effective, rapid and yet accurate methods for latent fingerprint detection and recovery. Herein, this paper reports the synthesis of bright blue photoluminescent carbon dots (C-dots) via an eco-friendly and simple one-step microwave-assisted carbonization of potato peels’ biomass. The C-dots were prepared in only 3 min and ground into powder and used without any further treatment. The as-prepared C-dots were characterized using atomic force microscope, Fourier transform infra-red spectroscopy and X-ray diffraction with an average size of 1.0[Formula: see text]nm. The optical properties of the as-prepared C-dots were studied by UV-Vis spectroscopy and spectrofluorometer which established an excitation and emission wavelengths of 390[Formula: see text]nm and 480[Formula: see text]nm, respectively. Owing to their strong solid state fluorescence, the as-prepared C-dots’ powder was successfully used in latent fingerprint detection and imaging on porous and nonporous surfaces. Latent fingerprints were recovered with high resolution and excellent quality providing sufficient details for individual identification. These findings demonstrate that C-dots derived from biomass have a great potential in latent fingerprint analysis for forensic applications.
Currently, illegal counterfeiting activities are increasing with the continuous developments of society and the fabrication of high security anti-counterfeiting techniques is becoming essential. The lanthanide-doped nanomaterials have great potential in anti-counterfeiting for their high luminescence intensity, narrow half-peak width and high stability. Herein, the dual-mode luminescent [email protected]2@TEuTbB nanomaterials have been successfully fabricated for anti-counterfeiting. Morphology, structure and luminesce properties of the synthetic samples have been investigated via TEM, XRD, FT-IR, XPS and fluorescence spectroscopy. The results present that the size of the synthetic materials is about 100 nm. The luminesce properties clearly show that the [email protected]2@TEuTbB nanomaterials can emit strong UC red color under the NIR light. Meanwhile, these materials can emit several DC luminescence colors by adjusting Eu³⁺ ions concentration under UV lamp. Furthermore, the lanthanide-doped nanomaterials are widely used in recognition of LFPs providing valuable evidence in forensic filed. As a result, the images of LFPs developed by the as prepared materials on various surfaces under UV lamp can be well visualized. The three levels details of fingerprints are clearly visible with high sensitivity, selectivity and contrast. Thus, these results confirm that the synthetized [email protected]2@TEuTbB nanospheres can provide a foundation for high-level anti-counterfeiting and the detection of fingerprints.
Herein, we report a green surface-state-controlling strategy to achieve the regulation of the photoluminescence (PL) properties of carbon dots (CDs)viafluorine (F)-doping techniques. Two types of F-doped CDs with different F contents (FCDs1andFCDs2) were prepared witho-phenylenediamine and its derivative as carbon precursorsviadifferent F-doping routes at room temperature. An obvious red-shift of PL for both the obtained CD products was achieved, due to the narrower band gap induced by F-doping.FCDs1exhibits favorable solid-state PL behaviors due to the alleviated aggregation-induced quenching attributed to the element-dilution effect and the formation of hydrogen bonds, and is used for latent fingerprint identification with high resolution.FCDs2with a high F content is characterized with a prominent red-shift of 70 nm and used as a powerful probe for the quantitative detection of cobalamin based on inner filter effects, giving a limit of detection of 0.15 μmol L
Carbon-dots (c-dots) have seen tremendous growth in the last decade as an optical sensing probe with applications ranging from metal ion detection, anion detection, disease biomarker detection with in vitro and in vivo applicability as sensors, bioimaging probes, and theranostics. The optical response, primarily the fluorescence turn-off/on signals, enable the use of c-dots as molecular electronics probe. A variety of sensors build using c-dot mimics the Boolean logic and are used to construct AND, OR, XOR, NOR, NAND, IMPLICATION, INHIBIT, YES, NOT, and higher order combinational logic gates. A number of keypad locks and memory elements have also been reported using c-dots. Herein, the molecular electronics potential of c-dots is delineated. The logic operation is discussed with the corresponding chemosensing ability. The applications in the areas of pattern recognition and anti-counterfeiting are also discussed briefly. The high biocompatibility of c-dots adds value to their in vivo applicability and this review envisions c-dot-based logic operation to provide deeper insights into biological studies in the near future.
Carbon dots(CDs) are a type of 1-10 nm nanosized particles with carbon as the main element. They show bright prospects in the field of fluorescence analysis and detection due to its many advantages, such as a wide range of synthetic raw materials, high biological safety, strong fluorescence signal, and stable optical properties. Latent fingerprint detection is a classical and reliable identification technology. Latent fingerprint is the trace of human finger secretions on solid contact surface which is hard to distinguish by naked eye. It needs to be processed by physical chemistry to enhance the imaging effect. The application of fluorescent carbon dots to enhanced imaging of latent fingerprints has given full play to the advantages of carbon dots and a series of advances have been made in recent years. In this paper, the common developing methods of latent fingerprints are introduced, the synthesis and preparation of carbon dots, luminescence mechanism, application in latent fingerprint detection, imaging mechanism and efficiency comparison are summarized. The deficiencies and future development direction of carbon dots in latent fingerprint detection are prospected, which provides an important reference for research work in related fields.
Because of direct π-π interactions and excessive energy resonance transfer, it is very challenging to prepare carbon dots (CDs) with a high fluorescence quantum yield (QY) in the solid state. In this study, novel CDs which gave solid-state fluorescence (SSF) with high brightness were successfully prepared via a simple microwave-assisted method. The prepared ScCDs can emit strong blue fluorescence in the solid state, and the absolute QY of this ScCDs powder reaches 51.7%. Such a high QY means that the ScCDs powder could be successfully applied in rapid latent fingerprint (LFP) detection. The LFP detection performance of this ScCDs powder was studied in detail, and the results show that the LFPs developed using the ScCDs powder can be visualized with high definition and contrast under different conditions. This research not only developed a new type of SSF-emitting CDs, but it also proved that the developed CDs have great potential for applications in LFP detection, and this research may also provide inspiration and ideas for the design of new SSF-emitting CDs.
Carbon dots, a kind of materials discovered nearly two decades ago, have attracted attention due to unique properties such as bright fluorescence emission, facile synthetic ways, high chemical and photostability, low cytotoxicity, good biocompatibility and environmental friendliness. The tunable fluorescence features caused widespread applicability in different scientific fields but mainly in biomedicine. However, the analytical methods that based on carbon dot fluorescence measurements are characterized by insufficient selectivity, weak anti-interference ability and moderate sensitivity. Thus, prior to utilization to highly complex biomedical samples, those materials have to be functionalized. Here, molecularly imprinted polymers are the class of materials, synthesized in the presence of template molecules, that provide sufficient selectivity, high cleanup capabilities as well as satisfactory enrichment potential. In this chapter, the biomedical application of molecularly imprinted polymer-functionalized carbon dots will be presented. The brief characterization of carbon dot synthetic approaches together with summarized overview of imprinting process and its limitations followed by detailed discussion of the current state of the art of the carbon dot molecularly imprinted polymer conjugates for biomedicine will provide insight into the future prospects of those advanced materials.
Room‐temperature phosphorescent (RTP) nitrogen‐doped carbon dots (N‐CDs) have attracted great interest but their efficiency is usually dependent on a solid matrix. Developing efficient matrix‐free RTP CDs is still a great challenge. Here, a simple strategy is reported to synthesize efficient matrix free RTP N‐CDs from citric acid (CA) and basic fuchsine (BF) via a single step hydrothermal process. The synthesized N‐CDs show strong fluorescence in aqueous solution and the solid state, and the RTP lifetime is long‐lived (51.9 ms at 298 K). The phosphorescence of the N‐CDs is attributed to the formation of an internal hydrogen bonded network by the organic polymers on the surface of the N‐CDs. This reduces the nonradiative transitions of the triplet excitons and mitigates oxygen quenching. The application of N‐CDs as security inks is demonstrated. Room‐temperature phosphorescent (RTP) nitrogen‐doped carbon dots (N‐CDs) are synthesized by a hydrothermal process. The synthesized N‐CDs show strong yellow solid state fluorescence and RTP properties. The phosphorescence lifetime and RTP mechanism are studied, and potential application of the N‐CDs in information security is confirmed.
We developed a water-soluble, stable and selective "turn-on" fluorescence sensing platform based on carbon quantum dots (CQDs) for rapid determination of phosphate (Pi) in aqueous solutions and for visualization of latent fingerprints on paper. The hydroxyl groups on the surface of the synthesized CQDs can be deprotonated by Pi to trigger the intramolecular charge transfer (ICT) process and the inhibition of excited-state proton transfer (ESPT), achieving a turn-on emission response. CQDs demonstrated the capability to selectively detect Pi over other common ions and biomolecules with the linear fluorescence intensity change in the range from 0 to 100 μM. Moreover, the paper sprayed with the CQD solution showed a remarkable blue emission speckle and a fingerprint upon addition of Pi solution and finger touching, respectively. Notably, the fingerprint images including level 3 details (crossover, bifurcation, termination, and island and sweat pores) are also clearly identified and distinguished, indicating their potential application in document security. We believe that the as-synthesized CQDs will provide a new tool for Pi detection in aqueous media and paper document security.
In this work, tubular boron carbon oxynitride (BCNO) phosphors with orange-emitting are synthesized by bamboo fiber assistance. The effects of different sintering temperatures on the structure, morphology, and photoluminescence (PL) performance of BCNO phosphors were investigated. The results revealed that with the increase of sintering temperature, compared with the BCNO synthesized without the template, the synthesized BCNO phosphor with bamboo fiber as template gradually becomes a hollow tubular structure. Meanwhile, when the sintering temperature is 700 ℃, the BCNO phosphor shows bright orange emission at 315 nm excitation wavelength, and the quantum yield (QY) is up to 75%. Moreover, the prepared BCNO phosphor has a sensitive and selective quenching effect on Fe³⁺ ion under 365 nm portable ultraviolet lamp irradiation. By using the obtained BCNO phosphor as a fluorescence labeling marker, the fingerprint recognition on the object surfaces also could be realized.
Light-emitting graphene quantum dots (GQDs) are widely investigated due to their distinct merits. However, GQDs generally suffer from aggregation-induced luminescence quenching, which means they are highly emissive in a solution state with uniform dispersion but dramatically quenched in a solid or aggregated state. This problem significantly limits the application of GQDs, partially in the solid-state light-emitting devices. In this report, we successfully developed a simple and efficient hydrothermal method for the production of nitrogen doped graphene quantum dots (N-GQDs) with strong solid-state fluorescence (SSF) by using citric acid and o-Phenylenediamine as precursors. Under the 365 nm UV light illumination, the produced N-GQDs in an aqueous state exhibit blue color, with a quantum yield of 58%. As the concentration of N-GQDs increases, the photoluminescence exhibits an obvious red-shift from blue to yellow. For the N-GQDs in solid state, yellow luminescence with a high photoluminescence quantum yield (PLQY) of 28% is achieved under the 405 nm excitation. Finally, via the simple adjustment of thickness and the concentration of N-GQDs in blue emitting InGaN chips, color converter is enabled by constructing white light-emitting diode (WLED) device with improved color rendering index (CRI) and correlated color temperature (CCT).
Carbon dots (CDs), a new member of the carbon‐based material family, possess unique properties, such as high fluorescence, non‐toxicity, eco‐friendliness, stability and cost‐effectiveness. These properties helped CDs to receive tremendous attention in various fields, namely, biological, opto‐electronic, bio‐imaging and energy‐related applications. Although CDs are widely explored in bio‐imaging and bio‐sensing applications, their effectiveness in forensic science and technology is comparatively new. In this review, applications of CDs pertaining to latent FPs recovery since 2015 to 2020 is summarized comprehensively.
Carbon dots (CDs) have gained scientific popularity due to their photoluminescence properties that are useful for the detection of hazardous materials. These safe and green nanomaterials can be synthesized from biowaste and chemicals using top-down or bottom-up methods. Hydrothermal and microwave-assisted synthesis methods are compared to reveal their simplicity and flexibility. CDs were hydrothermally synthesized between 180 °C and 200 °C within 2 to 12 h. The carbonation at a lower temperature could be offset by increasing the hydrothermal duration. Chemicals with higher purity resulted in higher quantum yield in general. The hydrothermal duration could be shortened to 1 h under microwave irradiation, but the quantum yield was not significantly improved even using a closed vessel under subcritical conditions. Additional nitrogen and sulfur dopants enhanced the optical and fluorescent properties, while the immobilization of CDs into a solid substrate facilitates the reuse. CDs could interact with heavy metals differently, resulting in quenching mechanisms such as static, dynamic, inner filter effect, and fluorescence resonance energy transfer. The photoluminescence changes allow the quantification of heavy metal concentrations such as mercury, copper, and lead concentration in water samples.
Lanthanide(III)-based luminescent materials have attracted great research interests due to their unique optical, electronic, and chemical characteristics. Up to now, how to extend these materials into large, broad application fields is still a great challenging task. In this contribution, we are intended to present a simple but facile strategy to enhance the luminescence from lanthanide ions and impart lanthanide(III)-based luminescent materials with more applicable properties, leading to meet the requirements from different purposes, such as being used as highly emissive powders, hydrogels, films, and sensitive probes under external stimuli. Herein, a water soluble, blue color emissive, temperature sensitive, and film-processable copolymer (Poly-ligand) was designed and synthesized. Upon complexing with Eu3+ and Tb3+ ions, the red color-emitting Poly-ligand-Eu and green color-emitting Poly-ligand-Tb were produced. After finely tuning the ratios between them, a standard white color emitting Poly-ligand-Eu1:Tb4 (CIE = 0.33 and 0.33) was obtained. Furthermore, the resulted materials not only possessed the emissive luminescent property but also inherited functions from the copolymer of Poly-ligand. Thus, these lanthanide(III)-based materials were used for fingerprint imaging, luminescent soft matters formation, colorful organic light-emitting diode device fabrication, and acid/alkali vapors detection.
Silicon quantum dots (Si QDs)-based solid-state fluorescent materials have attracted widespread attention in latent fingerprint detection due to the high photoluminescence, low toxicity and good stability. However, it is still challenging to fabricate solid-state Si QDs with high quantum yield because of the severe emission quenching of Si QDs. Herein, a one-step hydrothermal synthesis of polymer-like coated Si QDs with strong blue luminescence emission by using N-[3-(Trimethoxysilyl)propyl]ethylenediamine (DAMO), zinc chloride and sodium citrate as precursors is reported. The self-quenching-resistant polymer-like coated Si QDs powder is easily obtained by ethanol precipitation and oven drying, and the absolute photoluminescence quantum yield (PLQY) can reach up to 73.3%. The possible formation mechanism of polymer-like coated Si QDs is proposed. Because of the strong solid-state fluorescence, the Si QDs powder can be successfully applied in rapid latent fingerprint detection with enhanced imagining in various substrate surfaces.
Fluorescence quenching of carbon dots (CDs) occurs in their aggregated state ascribed to direct π–π interactions or excessive resonance energy transfer (RET). Thus, CDs have been severely restricted for applications requiring phosphors that emit in the solid state, such as the fabrication of white light-emitting diodes (WLEDs). In this report, novel CDs with bright solid-state fluorescence (SSF) were synthesized by simple microwave-assisted synthesis method, using 1,4,7,10-tetraazacyclododecane (cyclen) and citric acid as precursors. Under 365 nm UV light, these CDs emit bright yellow SSF, indicating they successfully overcome the aggregation-induced fluorescence quenching (ACQ) effect. When the excitation wavelength (λex) is fixed at 450 nm, the emission peak of the CDs is centered at 546 nm with the Commission Internationale de l’Eclairage chromaticity (CIE) coordinates of (0.43, 0.55), which means that they can be combined with a blue-emitting chip in order to fabricate WLEDs. More importantly, the absolute quantum yield (QY) of these CDs powder reached 48% at λex of 450 nm, which was much higher than many previously reported SSF-emitting CDs and indicating their high light conversion ability in solid-state. Thanks to the excellent optical property of these CDs powder, they were successfully used in the preparation of high-performance WLEDs. This study not only enriches SSF-emitting CD-based nanomaterials with good prospects for application, but also provides valuable reference for subsequent research on the synthesis of solid-state fluorescent CDs.
A novel bifunctional composite powder with moderate magnetic properties and intense fluorescence was prepared via a layer-by-layer assembly route. After the self-assembly procedure run up to 7 times, the as-prepared Fe3O4@SiO2-CD(n) began to overcome the quenching effect from Fe3O4 nanoparticles and shown intense blue emission (λem = 434 nm) under 370 nm UV irradiation with a quantum yield of 45.04%. The morphological characterization revealed that it has a spherical and uniform core-shell structure of approximately 120 nm in diameter. The component analysis and contact angle test manifested the hydrophilic groups on the surface of the final products. As a result, this novel nanocomposite powder has two advantages over traditional fingerprint powder in both morphology/size and organic functional groups, which could provide more suitable physical adsorption and more chemical bonding in the interaction between fingerprint residues and powders. A series of fingerprint enhancement experiments and a novel quantitative evaluation both confirmed its high contrast, high sensitivity, and especially high selectivity over traditional methods for latent fingerprints. More importantly, in addition to its saturation magnetization of 6.4 emu/g, the abundant hydrophilic groups on the surface of our composite powder also played an important role in absorbing moisture in air and print residues to avoid powder dust from the user’s respiratory tract. Therefore, a fast, user-secure, and highly selective method was established and expected to be valuable in forensic science and related fields.
Carbon‐based quantum dots (CQDs), including spherical carbon dots and graphene quantum dots, are an emerging class of photoluminescent (PL) materials with unique properties. Great progress has been made in the design and fabrication of high‐performance CQDs, however, the challenge of developing solid‐state PL CQDs have aroused great interest among researchers. A clear PL mechanism is the basis for the development of high‐performance solid‐state CQDs for light emission and is also a prerequisite for the realization of multiple practical applications. However, the extremely complex structure of a CQD greatly limits the understanding of the solid‐state PL mechanism of CQDs. So far, a variety of models have been proposed to explain the PL of solid‐state CQDs, but they have not been unified. This review summarizes the current understanding of the solid‐state PL of solid‐state CQDs from the perspective of energy band theory and electronic transitions. In addition, the common strategies for realizing solid‐state PL in CQDs are also summarized. Furthermore, the applications of CQDs in the fields of light‐emitting devices, anti‐counterfeiting, fingerprint detection, etc., are proposed. Finally, a brief outlook is given, highlighting current problems, and directions for development of solid‐state PL of CQDs.
A seeded growth method to produce colloidal carbon dots (CDs) through controlling the number of seeds and reaction time, which is demonstrated to be an effective way to tune their optical properties, is developed. Color‐tunable fluorescence of CDs with blue, green, yellow, and orange emissions under UV excitation is achieved by increasing the size of the seed CDs, with the color depending on the size of the π‐conjugated domains. Strong multicolor photoluminescence of powdered samples enables realization of efficient down‐conversion white‐light‐emitting devices with correlated color temperature ranging from 9579 to 2752 K and luminous efficacy from 19 to 51 lm W⁻¹. Moreover, color‐tunable room‐temperature phosphorescence of CD powders is demonstrated in the broad spectral range of 500–600 nm. It is related to the presence of the nitrogen‐containing groups at the surface of CDs, which form interparticle hydrogen bonds to protect the CD triplet states from quenching, and to the existence of the polyvinylpyrrolidone polymer chains at the surface of CDs. The color‐tunable room‐temperature phosphorescence from CDs demonstrated in this work exhibits potential for data encryption.
The emerging carbon quantum dots (CQDs) have been attracting significant attention for their prominent fluorescence, excellent stability and outstanding biocompatibility. Here, we report a facile one-step synthesis of highly fluorescent CQDs by using phthalic acid and triethylenediamine hexahydrate as precursors through a simple microwave-assisted method. The reaction time needed is only 60 s, which is less time-consuming than most previous reports. The phthalic acid with a benzene ring can improve the photoluminescence properties of CQDs as it can provide foreign sp² conjugating units, and then finally result in long-wavelength emission. The synthesized CQDs were fully characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Besides, the impacts of different freed ratio on physical and chemical properties of CQDs were investigated in detail. The prepared CQDs exhibited strong green fluorescence with a broad maximum emission wavelength. The quantum yields of the CQDs can reach 16.1% in aqueous solution and they were successfully used in cell imaging with good biocompatibility. Moreover, in solid state, the CQDs with the feed ratio of 1: 0.5 showed a strong green–yellow fluorescence which may have great potential to fabricate optoelectronic devices. Furthermore, the prepared CQDs also showed high pH sensitivity and can act as a fluorescence nanosensor for pH sensing.
It is demonstrated that treatment of blue‐emissive carbon dots (CDs) with aqueous hydrogen peroxide (H2O2) results in the green emissive solid state CD phosphor with photoluminescence quantum yield of 25% and short luminescence lifetime of 6 ns. The bathochromic‐shifted, enhanced green emission of H2O2‐treated CDs in the powder is ascribed to surface state changes occurring in the aggregated material. Using the green emissive H2O2‐treated CD phosphor, down‐conversion white‐light‐emitting devices with cool, pure, and warm white light are fabricated. Moreover, using the green emissive CD phosphor as a color converter, a laser‐based white‐light source is realized, and visible light communication with a high modulation bandwidth of up to 285 MHz and data transmission rate of ≈435 Mbps is demonstrated. Pure carbon dot (CD) phosphor with an intense green emission in the aggregated state (photoluminescence quantum yield up to 25%) is realized by a straightforward surface treatment method of blue‐emissive CDs with aqueous hydrogen peroxide solution. Using the CD phosphor as a color converter, visible light communication with high modulation bandwidth to 285 MHz and a data transmission rate of 435 Mbps is realized.
Non-toxic Au nanoclusters@montmorillonite (AuNCs@MMT) nanocomposites with strong red fluorescence are prepared by a microwave (MW)-assisted synthesis method and immobilize Au NCs into sodium MMT clay matrix via electrostatic interaction. Due to the immobilization of Au NCs in the layered structure of the MMT clay matrix, the formative AuNCs@MMT nanocomposites show high emission, stable chemical features and less toxicity. The obtained Au NCs and AuNCs@MMT nanopowders were characterized by using UV-visible absorption spectroscopy, fluorescence spectroscopy, infrared spectroscopy, TEM/HRTEM, SEM and XRD etc. to depict their sizes, microstructures and optical features. Due to their environmentally friendly preparation, time-saving procedure, user-friendly operation, low cost, efficient UV-visible radiation-dependent photoluminescence and good affinity with finger residues, the as-synthesized AuNCs@MMT nanopowders are employed as a alternative florescent developing reagent for enhancing latent fingerprints deposited on various object surfaces (such as glass, porcelain enamel, stainless steel, painted metal, plastic products, weighing papers etc.) for individual identification. As results, the enhanced fingerprints with clear patterns and satisfactory ridge details were obtained by using as-prepared AuNCs@MMT nanopowders. At the same time, intensively red fluorescence as well as good contrast without background staining of developed prints demonstrated great advantages for surfaces with multicolour. Because of their good sensitivity, non-toxicity and strong resistance to background interference, the as-prepared fluorescent nanocomposites are an actual alternative to conventional powdering reagents, which may find potential application in forensic detection.
Herein, we present a facile approach to produce long-wavelength emitting carbon dots (CDs). A shift of the fluorescence emission wavelength of CDs from 630 nm to 520 nm can be easily acquired. The as-synthesized CDs exhibit concentration-dependent PL property as well as the “solvatochromism” phenomenon, which are rarely known in CDs. As the concentration or solvent polarity of the CDs increases, the photoluminescence (PL) wavelength exhibits a red shift. More importantly, the QY of these long-wavelength CDs is as high as 52.4%, which is considerably higher than that mentioned in other reports. Moreover, on addition of an acid (HCl), the surface H⁺-functionalization on the CDs leads to strong quenching of fluorescence emission, which is almost reversible after the addition of a strong base (NaOH). Then, CDs based solid-state composites were fabricated using a combination of polyvinyl butyral (PVB) and CDs. Finally, CDs/PVB composites were deposited on the Ce³⁺:Y3Al5O12 (Ce³⁺:YAG) phosphor-in-glass (Ce-PiG) via a screen-printing technology. Warm white light-emitting diodes (WLEDs) were then fabricated using these materials and GaN chips. The results indicate that these CDs possess a potential for future applications in warm WLEDs.
Thermally activated delayed fluorescence (TADF) materials are inspiring intensive research in optoelectronic applications. To date, most of the TADF materials are limited to metal-organic complexes and organic molecules with lifetimes of several microseconds/milliseconds that are sensitive to oxygen. We report a facial and general “dots-in-zeolites” strategy to in situ confine carbon dots (CDs) in zeolitic matrices during hydrothermal/solvothermal crystallization to generate high-efficient TADF materials with ultralong lifetimes. The resultant CDs@zeolite composites exhibit high quantum yields up to 52.14% and ultralong lifetimes up to 350 ms at ambient temperature and atmosphere. This intriguing TADF phenomenon is due to the fact that nanoconfined space of zeolites can efficiently stabilize the triplet states of CDs, thus enabling the reverse intersystem crossing process for TADF. Meanwhile, zeolite frameworks can also hinder oxygen quenching to present TADF behavior at air atmosphere. This design concept introduces a new perspective to develop materials with unique TADF performance and various novel delayed fluorescence–based applications.
The residue obtained from the pyrolysis of waste polyolefins, has been used for preparation of highly green-visual fluorescent carbon quantum dots (CQDs) by a simple one step hydrothermal approach consisting of ultrasonic-assisted chemical oxidation. These CQDs were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, TEM, XRD, and FTIR. The CQDs possessed high stability in aque-ous solution and exhibited strong fluorescence with quantum yield of 4.84%. The use of these CQDs as a fluorescent sensor for Cu 2+ ions detection has been explored. The synthesized CQDs have excellent selectivity and sensitivity towards Cu 2+ ions with a limit of detection (LOD) 6.33 nM and linear detection range of 1-8.0 M. These CQDs have also shown their utility for analysis of real water samples and have the potential to use for triple negative breast cancer cells (MDA-MB 468 cells) imaging.
Carbon quantum dots (CDs) are a relatively new class of carbon nanomaterials which have been studied very much in the last fifteen years to improve their already favorable properties. The optical properties of CDs have drawn particular interest as they display the unusual trait of excitation-dependent emission, as well as high fluorescence quantum yields (QY), long photoluminescence (PL) decay lifetimes, and photostability. These qualities naturally lead researchers to apply CDs in the field of imaging (particularly bio-imaging) and sensing. Since the amount of publications regarding CDs has been growing nearly exponentially in the last ten years, many improvements have been made in the optical properties of CDs such as QY and PL lifetime. However, a great deal of confusion remains regarding the PL mechanism of CDs as well as their structural properties. Therefore, presented in this review is a summary and discussion of the QYs and PL lifetimes reported in recent years. The effect of method as well as precursor has been evaluated and discussed appropriately. The current theories regarding the PL mechanism of CDs are discussed, with special attention to the concept of surface state-controlled PL. With this knowledge, the improvement of preparation and applications of CDs related to their optical properties will be easily accomplished. Further improvements can be made to CDs through the understanding of their structural and optical properties.
Carbon dots (CDs), especially heteroatom doped CDs derived from natural resources, have attracted growing interest due to their multiple potential applications. In this work, nitrogen and sulfur co-doped CDs (N/S-CDs) with a high quantum yield of 13.3% were synthesized by a facile approach based on one-step combustion treatment of cellulose-based biowaste of willow catkin. Due to the existence of urea and sulfuric acid used in the combustion process, the generated yield of the obtained N/S-CDs was raised to be as high as 14.3%. N/S-CDs were characterized by high-resolution TEM, FT-IR spectroscopy, XPS spectroscopy and Raman spectroscopy. The formation mechanism of N/S-CDs was also explored. These N/S-CDs with an average diameter of 7.3 nm demonstrated superior photo-stability, low cytotoxicity, pH stability and could be used for selective and sensitive detection of Fe³⁺ ions. Furthermore, based on their favorable feature of excellent biocompatibility and Fe³⁺ ions detection capability, the use of such N/S-CDs for intracellular Fe³⁺ ions detection application was also demonstrated.
Carbon Dots (CDs) were obtained using a hydrothermal method and used for the detection of fingerprints through fluorescent imaging. Synthesized CDs exhibited a brightness emission at 495 nm, which
was related to their structural and chemical properties. The results of detailed surface characterizations by XPS, ss-NMR and fluorescence spectroscopies, suggested that the negative charge of the functionals groups promoted electrostatic interactions between the charged CDs surface functional groups (amine, amide and carboxylic) and the secretion components present in the thin layer of fluid left on the surface upon its direct contact with human fingers. The obtained results were validated by the scientific protocol
of the Police Automated Fingerprint Identification System (AFIS) based on a biometric identification.
Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.
Metal-free carbonaceous nanomaterials have witnessed a renaissance of interest due to the surge in the realm of nanotechnology. Among myriads of carbon-based nanostructures with versatile dimensionality, one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) carbon dots (CDs) have grown into a research frontier in the past decades. With extraordinary mechanical, thermal, electrical and optical properties, CNTs are utilized in transparent displays, quantum wires, field emission transistors, aerospace materials, etc. Although CNTs possess diverse characteristics, the most attractive property is their unique photoluminescence. On the other hand, another growing family of carbonaceous nanomaterials, which is CDs, has drawn much research fascination due to its cost-effective, low toxicity, environmental friendly, fluorescence, luminescence and simplicity to be synthesized and functionalized with surface passivation. Benefiting from these unprecedented properties, CDs have been widely employed in biosensing, bioimaging, nanomedicine, and catalysis. Herein, we have systematically presented the fascinating properties, preparation methods and multitudinous applications of CNTs and CDs (including graphene quantum dots) in this review. We will discuss how CNTs and CDs have emerged as auspicious nanomaterials for potential applications, especially in electronics, sensors, bioimaging, wearable devices, batteries, supercapacitors, catalysis and light-emitting diode (LED). Last but not least, this review is concluded with summary, outlooks and invigorating perspectives for future research horizons in this emerging platform of carbonaceous nanomaterials.
Aggregation-induced quenching (AIQ) of emission is an obstacle for the development of carbon dots (CDots) for solid-state luminescent devices. In this work, we introduce the way how to avoid AIQ and to produce highly luminescent CDots through a space-confined vacuum heating synthesis. Due to the presence of CaCl2, the mixture of citric acid and urea form an inflated foam under vacuum heating at 120°C. Gradually raising the heating temperature to 250°C, blue emissive molecular species are first formed, and are then transformed towards uniform-sized green emissive CDots through dehydration and carbonization processes taking place in the confined ultrathin space of the foam walls. The green luminescence of these CDots originates from conjugated sp2 domains, and exhibits high photoluminescence quantum yield (PLQY) of 72% in ethanol solution. Remarkably, due to the existence of only one type of recombination centers in these nanoparticles, the AIQ does not take place in CDot-based close-packed films, which keep strong emission with PLQY of 65%. Utilizing the differences in the emission properties of vacuum heating produced CDots, CDots synthesized through the microwave-assisted heating, and the commercial green fluorescent organic ink (namely, excitation-dependent vs. excitation-independent emission, and different stability against photobleaching), multilevel data encryption has been demonstrated.
A luminescent solar concentrator (LSC) is composed of loaded luminophores and a waveguide that can be employed to harvest and concentrate both direct and diffused sunlight for promising applications in solar windows. Thus far, most of efficient LSCs still relied on the heavy-metal-containing colloidal quantum dots (CQDs) dispersed into a polymer matrix with a very low loading (typically < 1 wt%). Such low-loading constraint is required to mitigate the concentration-induced quenching (CIQ) and maintain high optical quality and film uniformity, but this would strongly reduce the light-absorbing efficiency. To address all issues, greener LSCs with high loading concentration were prepared by in-situ cross-linking organosilane-functionalized carbon nano-dots (Si-CNDs) and their photophysical properties relevant to LSC operation were studied. The PL emission is stable and does not suffer from severe CIQ effect for cross-linked Si-CNDs even with 25 wt% loadings, thus exhibiting high solid-state quantum yields (QYs) up to after the calibration of the reabsorption losses. Furthermore, such LSCs can still hold high optical quality and film uniformity, leading to low scattering losses and high internal quantum efficiency of ~22%. However, the reabsorption losses need to be further addressed to realize large-area LSCs based on earth-abundant, cost-effective CNDs.
Recently, carbon dots have been emerged as novel luminous materials due to their excellent luminous performance. However, it is still challenging to obtain high quantum yields red emission carbon dots. Here, we synthesized new kind of high efficiency red emission carbon dots from 1,4-phenylene diisocyanate by solvothermal method. And the carbon dots were used to fabricate trichromatic white LEDs which possess high luminous efficacy and Color Rendering Index. This work proposed an approach for high quantum yield carbon dots by introducing more conjugated nitrogen groups in graphitic layered structure. Moreover, the high efficiency red emission carbon dots can greatly promote carbon dots’ application in white LEDs which demonstrate that the carbon dots are promising materials in LEDs, displays and even in other light fields.
In this report, a novel type of carbon dots (CDs) were prepared via a simple MW-assisted method by using citric acid and piperazine as precursors. The CDs can be obtained in large-scale and emit bright solid-state fluorescence (SSF) with different colors. Then the synthetic CDs were fully characterized with PL, UV, XPS, TEM, and FTIR and the relationship between the mass ratio of precursors and physicochemical property of the CDs was also investigated detailedly. The results showed that these CDs prepared at different mass ratios have different element content and functional group content. More importantly, the mass ratio of the precursors not only has a great influence on their particle sizes, but also can affect their PL properties. With the decreased of the mass ratio, their particle size decreased gradually and their emission wavelength gradually red-shift. This interesting finding may be helpful for fabricating CDs with controllable particle size and tunable light-emitting colors. Based on their excellent SSF property, these CDs were successfully used to fabricate light-emitting diodes (LEDs) and detect latent fingerprints (LFPs). In conclusion, the research may offer a valuable reference for obtaining CDs with SSF and developing LEDs phosphors and LFPs detection reagent.
It is still a challenging issue to achieve efficient and tunable fluorescent carbon dot (CD) powders. Herein, we report a novel and general solvothermal strategy to in-situ embedding CDs in trisodium citrate crystal matrix, and these CDs exhibit tunable emission from green to yellow and a high quantum yield up to 21.6% in solid state, comparable to that in solution. This intriguing fluorescence phenomenon may be caused by the space confinement from trisodium citrate crystal matrix, thus enabling CDs to effectively suppress the aggregation-induced luminescence quenching. The CD powders have been employed for fabricating white light-emitting devices on blue chips with adjustable color temperature. Moreover, solid-state lighting systems like flexible fluorescent films and plates have been demonstrated by using the CD powders as the luminescent medium. This work provides a facile way to achieve tunable solid-state fluorescence CD powders, which have promising applications in CDs-based luminescence devices.
A green and facile fermentation method for the synthesis of carbon based dots (CDs) has been developed for the first time. The fluorescence (FL) properties of the obtained CDs could be tuned by changing the kind of microbes. For instance, the fermentation of leaves with Bacillus subtilis produces red emission CDs, which show great application potential in bioimaging. The formation mechanism and the FL mechanism of the CDs have been well discussed. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Carbon dot (CD)-based solid-state fluorescent materials have attracted much attention in recent years owning to their superior optical and environment-friendly, thus demonstrating many potential applications. However, the previously reported CD-based solid-state fluorescent materials mostly assembled a kind of CDs in matrix with only single characteristic peak, and that of assembling double CDs are very rare with two characteristic peaks. Such a drackback restricts their further application, particularly in the white light emitting diodes (WLEDs) fields. Herein, A rare type of double CDs-based fluorescent materials has been synthesized with dual characteristic peaks at 420 nm and 635 nm via one-step assembling blue- and red-emissive carbon dots (bCDs, rCDs) into mesoporous aluminas (MAs). The MAs nonfluorescence matrix neither competes for absorbing excitation light nor absorbs the emissions of CDs, lending to excellent PL emitting, color and thermal stabilities. The emissive colors are tunable to white-light region just through adjusting excitation wavelengths, showing great potential in phosphor-based WLEDs. In the field of agricultural planting, transparent sunlight conversion film based on the co-assembled phosphors were obtained, revealing inherent optical properties and efficiently converting sunlight to blue and red lights, which are essential for plants photosynthesis.
A self-quenching-resistant and bright green emitting carbon dots (CDs) in solid state is synthesized via a facile hydrothermal method. Their structure, optical properties together with their thermal and photo-stabilities, as well as their applicability in white LEDs are investigated. The obtained CDs have nearly spherical shape with size around 4~5 nm. The resulting powder CDs show excitation-independent emission behavior, and can be excited over a broad range from 300-450 nm. Under optimal excitation at 400 nm, the resultant powder CDs yield bright and broad green emission around 505 nm with full width at half maximum (FWHM) about 110 nm. Time resolved and temperature dependent luminescence spectra suggest that the luminescence origin of the resulting CDs is one single species. The potential application of the green emitting CDs is evaluated by constructing a white light-emitting diodes lamp. The fabricated white LEDs lamp emitted bright warm white light with excellent color rendering properties (a color rendering index of 86.9 and correlated color temperature of 3863 K ).
Multiple-color-emissive carbon dots (CDots) have potential applications in various fields such as bioimaging, light-emitting devices, and photocatalysis. The majority of the current CDots to date exhibit excitation-wavelength-dependent emissions with their maximum emission limited at the blue-light region. Here, a synthesis of multiple-color-emission CDots by controlled graphitization and surface function is reported. The CDots are synthesized through controlled thermal pyrolysis of citric acid and urea. By regulating the thermal-pyrolysis temperature and ratio of reactants, the maximum emission of the resulting CDots gradually shifts from blue to red light, covering the entire light spectrum. Specifically, the emission position of the CDots can be tuned from 430 to 630 nm through controlling the extent of graphitization and the amount of surface functional groups, COOH. The relative photoluminescence quantum yields of the CDots with blue, green, and red emission reach up to 52.6%, 35.1%, and 12.9%, respectively. Furthermore, it is demonstrated that the CDots can be uniformly dispersed into epoxy resins and be fabricated as transparent CDots/epoxy composites for multiple-color- and white-light-emitting devices. This research opens a door for developing low-cost CDots as alternative phosphors for light-emitting devices.
The surface functionalization of carbon dots (CDs) can introduce an additional dimension for the control of their photoluminescence properties and effective promotion of the applications of CDs such as imaging, sensing, etc. In this study, a simple one-step carbonization using Tween 80 as the sole carbon source is described for directly synthesizing white-emitting CDs (WCDs) in high yield. The results revealed the presence of several long alkyl chains on the surface of the as-fabricated WCDs, which effectively suppress the aggregation-caused quenching (ACQ) effect and emit bright white luminescence under an UV illumination of 365 nm in the solution and solid states. Besides, together with the surface protection of long alkyl chains, WCDs preferentially interact with lipophilic fatty residues and are beneficial for the label-free imaging of latent fingerprints. This study provides a promising new method to not only effectively inhibit the intrinsic ACQ effect of CDs but also develop the surface engineering of functionalized white-emitting CDs for practical applications via facile synthesis.
Pursuit of low-cost and large-scale method to prepare carbon quantum dots (CQDs) is a persistent objective in recent years. In this work, we have successfully synthesized a series of nitrogen-doped carbon quantum dots (N-CQDs) under different hydrothermal temperature employing Eichhornia crassipes (ECs) as precursors. Considering the pollution ability to water and low-cost, this study may direct the novel path to convert waste material to useful quantum dots. After measurements such as TEM, XRD, Raman, XPS, PL as well as the UV–vis absorbance ability, outstanding optical properties have been discovered. In this fashion, solar cells are tentative to be fabricated, yielding the maximized solar-to-electrical conversion efficiency of 0.17% with a good fill factor of 67%. Meanwhile, the above-mentioned quantum dots also show the up-conversion ability, suggesting the potential application in infrared detection or broadening light-absorbing devices.
The use of carbon-based dots (C-bDs), involving carbon dots, carbon quantum dots, and graphene quantum dots, as a new class of photoluminescent nanomaterials is rapidly expanding. Their many advantages including water solubility, high stability, low toxicity, ease of functionalization, and cost-efficient and simple synthetic routes have introduced them as potential alternatives to conventional semiconductor-based quantum dots. However, difficulty in preparing long-wavelength and multicolor-emitting C-bDs has caused some major disadvantages for these nanomaterials and limited their application in fields such as bioimaging and multicolor patterning. Although different emission colors from C-bDs can be observed by varying their excitation wavelength, this is not identified as real photoluminescence tuning, and in fact, preparing C-bDs with such special photoluminescence properties has proven to be a challenging task. This review summarizes to date successes in preparing long-wavelength, multicolor, and white-light-emitting C-bDs along with their potential applications. We discuss the developments in using specific precursors, synthetic methods, heteroatom doping, and post treatments such as separation and surface modification methods that have led to C-bDs with unique emission colors.
Carbon quantum dots (CQDs) have emerged as potential alternatives to classical metal-based semiconductor quantum dots (QDs) due to the abundance of their precursors, their ease of synthesis, high biocompatibility, low cost, and particularly their strong photoresponsiveness, tunability, and stability. Light is a versatile, tunable stimulus that can provide spatiotemporal control. Its interaction with CQDs elicits interesting responses such as wavelength-dependent optical emissions, charge/electron transfer, and heat generation, processes that are suitable for a range of photomediated bioapplications. The carbogenic core and surface characteristics of CQDs can be tuned through versatile engineering strategies to endow specific optical and physicochemical properties, while conjugation with specific moieties can enable the design of targeted probes. Fundamental approaches to tune the responses of CQDs to photo-interactions and the design of bionanoprobes are presented, which enable biomedical applications involving diagnostics and therapeutics. These strategies represent comprehensive platforms for engineering multifunctional probes for nanomedicine, and the design of QD probes with a range of metal-free and emerging 2D materials.
Carbon quantum dots (CQDs) have attracted much attention owing to their unique optical properties and a wide range of applications. The fabrication and control of CQDs with organic solubility and long-wavelength emission are still urgent problems to address for their practical use in LEDs. Here, organic-soluble CQDs were produced at a high yield of ~90% by a facile solvent engineering treatment of 1,3,6-trinitropyrene, which simultaneously as the nitrogen source and carbon sources. The optical properties of the organic-soluble CQDs (o-CQDs) were investigated in nonpolar and polar solvents, films, and LED devices. The CQDs have a narrow size distribution around 2.66 nm, and can be dispersed in different organic solvents. Significantly, as-prepared CQDs present an excitation-independent emission at 607 nm with a fluorescence quantum yields (QYs) up to 65.93% in toluene solution. A pronounced solvent effect was observed and their strong absorption bands can be tuned in the whole visible region (400-750 nm) by changing the solvent. The CQDs in various solvents can emit bright, excitation-independent, long-wavelength fluorescence (orange to red). What’s more, benefiting from the unique oil-solution properties, as-prepared CQDs can be processed in thin film and device forms to meet the requirements of various applications, such as phosphor-based white-light LEDs. The color coordinate for these CQDs modified LED is realized at (0.32, 0.31), which is close to pure white light (0.33, 0.33).
A one-pot microwave-assisted hydrothermal approach was developed to quickly synthesize organosilane-functionalized carbon dots (Si-CDs) within 5 minutes. With the assistance of N-(β-Aminoethyl)-γ-aminopropyl trimethoxysilane (KH-792) as distance barrier chains, the aggregation-caused quenching is suppressed successfully, which contributes to solid-state Si-CDs emitting bright blue fluorescence (λem~454 nm). The photoluminescence quantum yield of as-prepared Si-CDs in solid state reaches 65.8% with an optimized molar ratio of the reactant citric acid to KH-792 of 1:5 and the reaction temperature of 180°C, which is 2.5-fold that of their solution. Together with their good film-forming ability and thermal stability, Si-CDs were applied to fabricate a white-light-emitting device with the color coordinates of (0.32, 0.36) and the correlated color temperature of 6071 K. Our results indicate that the as-prepared Si-CDs are promising materials with efficient solid-state emission to be used in the lighting, backlight display and other optoelectronic devices.
g-C3N4 (gCN) with nitrogen vacancy has been extensively investigated and applied in (photo)catalysis. Engineering the carbon vacancy in gCN is of great importance, but it remains a challenging task. In this work, we report for the first time the fabrication of gCN with carbon vacancy (Cv-gCN) via thermal treatment of pristine gCN in CO2 atmosphere. The photocatalytic performance of Cv-gCN is evaluated on the basis of NO oxidization under visible light irradiation (λ > 400 nm) in a continual reactor. The successful formation of carbon vacancy in gCN is confirmed through electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The photocatalytic oxidation removal rate of NO over Cv-gCN is 59.0%, which is two times higher than that over pristine gCN (24.2%). The results of the quenching experiment show that superoxide radicals (O2⁻) act as the main reactive oxygen species, which is responsible for the oxidation of NO. The enlarged BET surface areas and negatively shifted conduction band (CB) potential enhance the photocatalytic activity of Cv-gCN, which facilitates the efficient electron transfer from the CB of Cv-gCN to the surface adsorbed oxygen, resulting in the formation of O2⁻ that can oxidize NO.
Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.
Stable solid-state red fluorescence from organosilane-functionalized carbon dots (CDs) with sizes around 3 nm is reported for the first time. Meanwhile, a novel method is also first reported for the efficient construction of dual-fluorescence morphologies. The quantum yield of these solid-state CDs and their aqueous solution is 9.60 and 50.7%, respectively. The fluorescence lifetime is 4.82 ns for solid-state CDs, and 15.57 ns for their aqueous solution. These CDs are detailedly studied how they can exhibit obvious photoluminescence overcoming the self-quenching in solid state. Luminescent materials are constructed with dual fluorescence based on as-prepared single emissive CDs (red emission) and nonfluorescence media (starch, Al2 O3 , and RnOCH3 COONa), with the characteristic peaks located at nearly 440 and 600 nm. Tunable photoluminescence can be successfully achieved by tuning the mass ratio of CDs to solid matrix (such as starch). These constructed dual-fluorescence CDs/starch composites can also be applied in white light-emitting diodes with UV chips (395 nm), and oxygen sensing.
Aggregation-induced luminescence quenching of carbon dots (CDots) is the main obstacle for their applications in the solid state. Herein, we report a method to produce strongly luminescent CDots@silica composite gels with high concentrated emitting centers, where the gelation of tetraethyl orthosilicate is initiated by the surface hydroxyl groups of CDots. The key feature of this approach is to prevent both the collision between high concentrated CDots in gelating solution and their aggregation upon drying. The resultant CDots@silica composite xerogel exhibits both high CDots loading fraction (19.2 wt%) and photoluminescence quantum yields exceeding 40%.
Development of efficient, inexpensive, and environmentally-friendly light emitters, particularly devices that produce white light, have drawn intense interest due to diverse applications in the lighting industry, photonics, solar energy, and others. We present a simple strategy for fabrication of flexible transparent films exhibiting tuneable light emission through one-pot synthesis of polymer matrixes with embedded carbon dots assembled in-situ. Importantly, different luminescence colours were produced simply by preparing C-dot/polymer films using carbon precursors that yielded C-dots exhibiting distinct fluorescence emission profiles. Furthermore, mixtures of C-dot precursors could be also employed for fabricating films exhibiting different colours. In particular, we successfully produced films emitting white light with attractive properties (i.e. “warm” white light with high colour rendering index) – a highly sought goal in optical technologies.
Fingerprints function as an indispensable tool in forensic investigations and personal identification, as well as in our daily life for many other purposes, such as safety inspection, access control, and individual credentials. To date, although innumerable methods have been exploited for fingerprint detection, a simple, rapid, and easy-processing method is still needed. Herein a negative imaging approach for developing latent fingerprints was presented, based on spatial selective control of electrochemiluminescence generation of luminol at the electrode surface. Factors, including the co-reactants, applied potential and the concentration of ECL luminophore, were investigated to achieve a satisfactory visualization enhancement. This imaging approach is simple, rapid, and no pre-treatment either on the background or on the fingerprint itself is needed. It constitutes a new approach and new idea for both fingerprint development and electrochemical imaging technique.
Self-quenching in the aggregation state is overcome, and tunable solid-state photoluminescence of carbon-dot powder is achieved. Furthermore, based on the controllable optical property in organic solvents, a novel concept, i.e., constructing dual-fluorescence morphologies from single luminescent species, is presented to realize white light-emission.
A unique dual-emitting core-shell carbon dot-silica-phosphor (CDSP) was constructed from carbon dots (CDs), tetraethoxysilane (TEOS) and Sr2Si5N8:Eu(2+) phosphor through a one-pot sol-gel method. Blue emitting CDs uniformly disperse in the silica layer covering the orange emitting phosphor via a polymerization process, which makes CDSP achieve even white light emission. Tunable photoluminescence of CDSP is observed and the preferable white light emission is achieved through changing the excitation wavelength or controlling the mass ratio of the phosphor. When CDSP powders with a phosphor rate of 3.9% and 5.1% are excited at a wavelength of 400 nm, preferable white light emission is observed, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.32, 0.32) and (0.34, 0.32), respectively. Furthermore, CDSP can mix well with epoxy resin to emit strong and even white light, and based on this, a CDSP-based white LED with a high colour rendering index (CRI) of 94 was fabricated.
One important resource for material synthesis is waste. Utilization of waste as a resource for material synthesis is an environmentally responsible approach that reduces the need for virgin resources and subsequent processing. In this report a method to produce multicolored, luminescent carbon dots (CDs) and subsequent fabrication of light emitting diodes from food, beverage, and combustion wastes, is discussed. Apart from food and beverages, combustion exhaust was also utilized for CDs production. Optical characterization results suggest that CDs from waste food and beverages are more luminescent than those produced from combustion waste.
Carbon dot (CD) doped sodium borosilicate gel (CD-NBS gel) glasses were successfully prepared by incorporating the CDs into sodium borosilicate networks. The structural and luminescent properties of highly flexible CD-NBS gel glasses with the concentrations of CDs from 5% to 70 wt% were studied. TEM images of the CD-NBS gel glasses demonstrated their uniformity and good dispersion. The red-shifted emission and enhanced quantum efficiency were obviously observed when the doping concentration of CDs in the gel glasses increased. The enhanced fluorescence properties of CD-NBS gel glasses were considered to originate from surface modification of CDs with high dopant concentration in the gel glasses. The CDs based white light-emitting diodes (W-LEDs) were developed by combining the yellow-emitting CD-NBS gel glasses with blue GaN-based LED chips. The as fabricated W-LEDs exhibited the optimized color coordinate of (0.32, 0.33), the color rendering index up to 78.9, and maximum luminous efficacy exceeding 58.1 lm/W by use of the CD-NBS gel glasses with different loading fraction of CDs. These results indicated that the new kind of CD-NBS gel glasses would be a promising candidate for W-LEDs.
The incorporation of a minor amount of carbogenic nanoparticles into powder compositions imparts remarkable colour-tuneability, without compromising the flowability. In a proof-of-concept demonstration we report the use of these hybrid nanopowders for the visual enhancement of latent fingerprints where they effectively resolve issues arising from poor contrast against multi-coloured or patterned backgrounds.
Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.