Article

A Universal Photochemical Approach to Ultra-Small, Well-Dispersed Nanoparticle/Reduced Graphene Oxide Hybrids with Enhanced Nonlinear Optical Properties

Wiley
Advanced Optical Materials
Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Integrating multiple functionalities into individual nanoscale hybrids with strong nonlinear optical (NLO) response to ultrafast laser pulses is of tremendous importance. Here, a series of ultra-small and well-dispersed nanoparticles (NPs) supported on the undoped and doped reduced graphene oxide (rGO) are obtained via a general and versatile photochemical technique. Extremely fast heterogeneous nucleation rate and cooling rate having negligible thermal effect induced by a femtosecond laser are proposed to play a determined role in the formation of ultra-small NPs. No surfactants, reduction reagents, or toxic materials are needed. The prepared rGO hybrids exhibit significantly enhanced ultrafast NLO response with very low optical limiting threshold, which originates from the fast and efficient electron and/or energy transfer from ultra-small NPs to rGO. This study may represent an important universal step toward the generation of graphene hybrid nanostructures and even complex 3D functional systems consisting of multiple functional ultra-small subunits with new horizons for numerous applications, especially in ultrafast nonlinear optics.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Various multifunctional materials have been attached to GO, including organic materials, dye ionic molecules, and dielectric and metallic nanoparticles. [6][7][8][9][10][11][12] Enhanced optical nonlinearities of such functionalized GO hybrid materials have been discovered and are attributed to strong interactions between GO and the functionalizing materials. However, the current results of hybrid GO materials are mostly limited to the hybrid GO solutions, [6][7][8][9][10][11] which create the main barrier for solid-state integrated photonic applications. ...
... [6][7][8][9][10][11][12] Enhanced optical nonlinearities of such functionalized GO hybrid materials have been discovered and are attributed to strong interactions between GO and the functionalizing materials. However, the current results of hybrid GO materials are mostly limited to the hybrid GO solutions, [6][7][8][9][10][11] which create the main barrier for solid-state integrated photonic applications. Studies on the nonlinear refraction (Kerr effect) of GO hybrid materials, especially the GO hybrid films, which is essential for on-chip signal regeneration, all-optical switching, and fast optical communications, 13 have remained largely unexplored. ...
... Studies on the nonlinear refraction (Kerr effect) of GO hybrid materials, especially the GO hybrid films, which is essential for on-chip signal regeneration, all-optical switching, and fast optical communications, 13 have remained largely unexplored. 9 Moreover, though different strategies have been used to effectively functionalize GO, including chemical, 6-9 laser-induced photochemical, 10 and laser ablation methods, 11 they require either environmentally hazardous chemicals or complex experimental setups, which largely restrict both the versatilities and flexibilities of the hybrid GO materials. ...
Article
Full-text available
We report a flexible method to functionalize highly transparent graphene oxide (GO) film with gold nanoparticles (AuNPs). Nonlinear absorption and refraction of the hybrid films are measured, which are strongly enhanced and tunable by different AuNP concentrations compared to both GO and AuNP-only samples. The enhanced nonlinearity is due to the effective functionalization of the hybrid films, which is verified by the ultraviolet-visible and Fourier-transform infrared spectra. Our low-loss hybrid GO-AuNP films provide a solid-state material platform for diverse nonlinear applications. The functionalizing method can serve as a universal strategy to manipulate the physical properties of hybrid GO.
... Metal nanoparticles wrapped in two-dimensional materials such as graphene oxide (GO) have captivated much attention due to their excellent linear and nonlinear optical (NLO) features [45][46][47]. Since it was first studied by Wang et al., so many related studies have been performed to realize the optical limiting response and the fundamental processes of carbonaceous materials, such as graphene, graphene oxide (GO), and composites of graphene [48][49][50]. NLO responses of silver incorporated graphene in picoseconds regime by Z-scan technique under the excitation wavelength, 1064 nm was investigated by Kalanoor et al. [51]. Sadrolhosseini et al. have studied the NLO features of the Au-GO nanocomposites, synthesized by pulsed laser ablation technique [52]. ...
... Energy (µJ) β eff (× 10 −10 mW −1 ) Ag-GO@ 532 nm 40 1. 5 29 The numerically calculated values of nonlinear optical parameters of the samples produce better insights toward the OL features of the Ag-GO nanohybrids synthesized via pulsed laser ablation, particularly in the nanosecond regime in a very short span time (15 min ablation time). Compared to the previous reports, the NLO responses of laserinduced colloidal Ag-GO nanohybrid materials in nanosecond regime are less investigated, and the present work establishes the wavelength and ablation time-dependent in-situ growth of metal NPs ornamented 2D hybrid materials for the first time [50,52,81]. The nonlinear optical response of the Ag-GO nanohybrid materials obtained at higher ablation times can be explored in future advancements of this work, and the tunability in the unique structural and morphological features of such samples pave the way to explore possibilities with its synergistic effects for getting far better OL properties. ...
Article
Full-text available
The demand for metallic nanoparticle ornamented nanohybrid materials of graphene oxide (GO) finds copious recognition by virtue of its advanced high-tech applications. Far apart from the long-established synthesis protocols, a novel laser-induced generation of silver nanoparticles (Ag NPs) that are anchored onto the GO layers by a single-step green method named pulsed laser ablation has been exemplified in this work. The second and third harmonic wavelengths (532 nm and 355 nm) of an Nd:YAG pulsed laser is used for the production of Ag NPs from a bulk solid silver target ablated in an aqueous solution of GO to fabricate colloidal Ag-GO nanohybrid materials. UV-Vis absorption spectroscopy, Raman spectroscopy, and TEM validate the optical, structural, and morphological features of the hybrid nanomaterials. The results revealed that the laser-assisted in-situ deposition of Ag NPs on the few-layered GO surface improved its antibacterial properties, in which the hybrid nanostructure synthesized at a longer wavelength exhibited higher antibacterial action resistance to Escherichia coli (E. coli) than Staphylococcus aureus (S. aureus) bacteria. Moreover, nonlinear optical absorption (NLA) of Ag-GO nanohybrid was measured using the open aperture Z-scan technique. The Z-scan results signify the NLA properties of the Ag-GO hybrid material and have a large decline in transmittance of more than 60%, which can be employed as a promising optical limiting (OL) material.
... As a comparison, the absorption shoulder at 305 nm of rGO disappears and the absorption in the whole visible light range increases after laser irradiation, indicating the reduction in GO (the colour change of GO before and after laser irradiation are given by inset (i) and (ii) of figure 2d). When GO solution mixed with Ag ions is reduced (as shown by inset (iii) of figure 2d), an obvious absorption peak at 420 nm is observed which can be attributed to the surface plasmon resonance (SPR) of Ag NPs [13,34]. The SPR peak of Ag NPs is enhanced by increasing the irradiation time, indicating that the reduction degree of the Ag ions is increased. ...
... The inset of figure 3a indicates the HRTEM image of Ag NPs. Obvious lattice fringes with the spacing of 0.24 nm are observed, which can be attributed to the (111) plane of the Ag crystallite [13,34]. irradiation, Ag NPs with high concentration are well dispersed on the rGO nanosheets, and the average size is evaluated to be about 16.1 nm. ...
Article
Full-text available
Reduced graphene oxide (rGO) functionalized with silver nanoparticles (Ag NPs) is prepared using a femtosecond laser ablation in liquids method. By ablating the mixed aqueous solutions of silver nitrate and graphene oxide (GO) using femtosecond laser pulses, Ag ions and GO are simultaneously reduced and well-dispersed Ag NPs supported on rGO are obtained. The effect of laser power, irritation time and Ag ion concentration on the optical property and morphology of the products are systematically studied. The nonlinear optical responses of the functionalized graphene are studied using a nanosecond Z-scan technique. The rGO hybrid shows an enhanced nonlinear absorption (NLA) effect compared with GO and rGO, and thus exhibits an excellent optical limiting (OL) property with very low activating threshold, which is estimated to be about 0.38 J cm⁻². The enhanced NLA effect in rGO hybrids makes it possible to fabricate solid-state optical limiter, improving the practicality of graphene materials in the OL area.
... [12][13][14] Recently, the irradiation with fs laser pulses has become an efficient technique for the fabrication and modification of carbonbased materials. [15][16][17][18][19] For modification of graphene, cutting, doping, defect introduction, folding, etc., have been implemented successfully. 14,[18][19][20][21][22][23][24] In addition, the advantage of fs-laser microprocessing of 2D materials enables costeffective fabrication of micro-or nano-structures towards various devices. ...
... [15][16][17][18][19] For modification of graphene, cutting, doping, defect introduction, folding, etc., have been implemented successfully. 14,[18][19][20][21][22][23][24] In addition, the advantage of fs-laser microprocessing of 2D materials enables costeffective fabrication of micro-or nano-structures towards various devices. 20,25,26 Nevertheless, the details of localized modification due to the fs laser irradiation on graphene require further investigation in order to obtain a better understanding of the laser-induced effect, which is helpful to realize more precise engineering of the micro-or nanoscale patterns in single-layer materials. ...
Article
Permanent micro-modifications in single-layer graphene with a spontaneous periodic structural change have been induced by femtosecond (fs) laser irradiation. These modifications present a regular variation along the radial direction from a central ablated region. Based on the obtained micro-Raman spectrum and the reflective micro-spectrum of laser-irradiated graphene, structural modification with periodic variations containing several spectral regimes has been observed, which was in good agreement with periodic topography of the structure observed using an atomic force microscope. It has also been found that several regions of the laser induced structures were with different optical properties, which were identified to be correlated with different modification mechanisms. In addition, after fs laser processing, graphene still maintains crystallinity. This work may be helpful for the development of graphene-based microstructures or devices by fs laser pulses.
... Notwithstanding, the enhancements were minimal. Recent studies have shown that attaching metal (Ag/Au) and semiconducting (ZnO) nanoparticles onto GO can enhance the ESA [19][20][21][22][23]. For example, B. S. Kalanoor et al have demonstrated ESA in Ag nanoparticle functionalized graphene composite at high peak intensity of 13 GW/cm 2 . ...
Preprint
Nonlinear optical absorption of light by materials are weak due to its perturbative nature, although a strong nonlinear response is of crucial importance to applications in optical limiting and switching. Here we demonstrate experimentally and theoretically an extremely efficient scheme of excited state absorption by charge transfer between donor and acceptor materials as the new method to enhance the nonlinear absorption by orders of magnitude. With this idea, we have demonstrated strong excited state absorption (ESA) in reduced graphene oxide that otherwise shows increased transparency at high fluence and enhancement of ESA by one orders of magnitude in graphene oxide by attaching gold nanoparticles (AuNP) in the tandem configuration that acts as an efficient charge transfer pair when excited at the plasmonic wavelength. To explain the unprecedented enhancement, we have developed a five-level rate equation model based on the charge transfer between the two materials and numerically simulated the results. To understand the correlation of interfacial charge-transfer with the concentration and type of the functional ligands attached to the graphene oxide sheet, we have investigated the AuNP-graphene oxide interface with various possible ligand configurations from first-principles calculations. By using the strong ESA of our hybrid materials, we have fabricated liquid cell-based high-performance optical limiters with important device parameters better than that of the benchmark optical limiters.
... Since it was first studied by Wang et al [23], some works have been conducted to understand the OL properties and the underlying mechanisms of carbonaceous materials, like graphene, graphene oxide (GO) and graphene nanocomposites [24,25]. The key mechanism behind the limiting action is attributed to the nonlinear scattering effect, where solvent microbubbles and/or microplasmas were produced as a result of interaction with intense light fluence, causing the attenuation of the incident light beams. ...
Article
Full-text available
Here we report a drastic enhancement of nonlinear absorption behaviour and exceptional optical limiting action of two core-shell systems (Au@graphite and Ag@graphite) prepared by adopting a fairly easy way in which we did not use any graphitic substrate. We carried out pulsed laser ablation of Au and Ag targets in toluene, monosubstituted benzene from which graphite layers of nanometer thickness has emerged as a result of photochemical reactions. The prepared samples were characterized and analyzed by UV/Vis spectroscopy, Raman spectroscopy, and TEM. Theoretical simulations of the core-shell nanostructures were done by the finite-difference time-domain method underlined the quenching of SPR in the case of both Au and Ag NPs by the graphitic layers evolved from toluene. Au and/or Ag@graphite core-shell structure exhibited a huge improvement in the nonlinear absorption behaviour and the optical limiting efficiency of these systems is found to be better than that of many benchmark optical limiters. The enhancement in nonlinear absorption property and the limiting actions of these systems were attributed to the enhanced excited-state absorption as well as free-carrier absorption arose as a result of the modification in the electronic structure of graphite on core-shell formation. Moreover, the metallic NPs also enhances nonlinear absorption through free-carrier absorption free-carrier absorption. So we believe these results are quite useful for guiding the characterization, monitoring the synthesis of similar nanostructures and for, the development of nanohybrids with desired properties for nonlinear optical, optoelectronic and photocatalytic applications.
... Nowadays, high-power short-pulse lasers, laser radiation has become a growing problem threatening the human eye, important optoelectronic devices, weapon systems and satellite photoelectric sensors [2]. Therefore, the development of effective laser protectors to protect the human eye and all photoelectric sensors from temporary or permanent damage caused by laser beams is not only of military significance but also of concern to the growing issue of social and public safety [3][4][5][6][7]. ...
Article
Four sandwich phthalocyanines with different rare earth metals (La, Y, Yb and Sc) are synthesized to investigate the influence of aggregation on nonlinear optical limiting effect. Hyperchem fitting results show that the distance between the phthalocyanine rings of the four phthalocyanine compounds is 2.81, 2.69, 2.56 and 2.38 Å for LaPc (Tetra-β-(4-nitro) lanthanum phthalocyanine), YPc (Tetra-β-(4-nitro) yttrium phthalocyanine), YbPc (Tetra-β-(4-nitro) ytterbium phthalocyanine) and ScPc (Tetra-β-(4-nitro) scandium phthalocyanine), respectively. As the radius of rare earth ions decreases, the interlayer spacing between phthalocyanine rings decreases, which greatly increases the degree of aggregation between phthalocyanine rings. As a result, the photophysical and nonlinear absorption coefficients of different rare-earth phthalocyanines also show regular changes. The nonlinear absorption coefficients of the four rare-earth phthalocyanines were LaPc (β = 1.86ⅹ10 − 10 m/W), YPc (β = 9.78ⅹ10 − 11 m/W), YbPc (β = 6.63ⅹ10 − 11 m/W), ScPc (β = 7.43ⅹ10 − 11 m/W), respectively, indicating that the degree of aggregation between phthalocyanine rings gradually increases as the radius of rare earth metals changes from La, Y, Yb, to Sc, which inhibits the reverse saturable absorption process of the triplet states, resulting in a gradual decrease of the nonlinear absorption coefficient. The experimental results fully reveal the effect of the aggregation effect between phthalocyanine rings on photophysical and nonlinear optical properties, and would provide a theoretical basis for the design of high-performance nonlinear optical materials.
... In recent years, femtosecond laser pulse irradiation has become suitable for processing of carbon-based materials, such as graphene oxide (GO) reduction [157][158][159][160]. Complex patterns on GO films can be created through direct femtosecond laser reduction [161]. ...
Article
Full-text available
Femtosecond laser fabrication has grown to be a major method of extreme manufacturing because of the extreme energy density and spatial and temporal scales of femtosecond lasers. The physical effects and the mechanism of interaction between femtosecond lasers and materials are distinct from those in traditional processes. The nonlinear and nonequilibrium effects of the interaction have given rise to new concepts, principles, and methods, such as femtosecond pulse durations are shorter than many physical/chemical characteristic times, which permits manipulating, adjusting, or interfering with electron dynamics. These new concepts and methods have broad application prospects in micro/nanofabrication, chemical synthesis, material processing, quantum control, and other related fields. This review discusses the cutting-edge theories, methods, measurements, and applications of femtosecond lasers to micro/nano-manufacturing. The key to future development of femtosecond laser manufacturing lies in revealing its fabrication mechanism from the electronic level and precisely regulating the electronic dynamics.
... In the past few years, significant hard work has been done for the preparation of graphene-based laser-assisted photo reduction [62][63][64]. Photo-thermal reduction [65][66], photochemical reduction [67][68][69][70] and microwave re-duction [71][72][73]. The laser-assisted technique is easy, catalyst-free, ecofriendly and the method does not generate toxic gases. ...
Article
Redox homeostasis is important for the maintenance of cell survival. Under physiological conditions, redox system works in a balance and involves activation of many signaling molecules. Regulation of redox balance via signaling molecules is achieved by different pathways and proteasomal system is a key pathway in this process. Importance of proteasomal system on signaling pathways has been investigated for many years. In this direction, many proteasome targeting molecules have been developed. Some of them are already in the clinic for cancer treatment and some are still under investigation to highlight underlying mechanisms. Although there are many studies done, molecular mechanisms of proteasome inhibitors and related signaling pathways need more detailed explanations. This review aims to discuss redox status and proteasomal system related signaling pathways. In addition, cancer therapies targeting proteasomal system and their effects on redox-related pathways have been summarized.
... [14,15] Since the discovery of single layer graphene in 2004, the optical limiting properties of graphene and graphene-like 2D materials have been studied comprehensively. [16][17][18][19][20][21] Significant progress has been made in the development of graphene-like 2D optical limiting materials, such as transition metal dichalcogenides (TMDs, e.g., MoS2, [19] WS2, [20] ) and black phosphorous (BP) [21] . To further compare the reported 2D optical limiting materials, we find the zero bandgap and weak electronic on/off ratio of graphene limits their use in nonlinear optical applications. ...
... Notwithstanding, the enhancements were minimal. Recent studies have shown that attaching metal (Ag/Au) and semiconducting (ZnO) nanoparticles onto GO can enhance the ESA [19][20][21][22][23]. For example, B. S. Kalanoor et al have demonstrated ESA in Ag nanoparticle functionalized graphene composite at high peak intensity of 13 GW/cm 2 . ...
Article
Full-text available
Nonlinear optical absorption of light by materials is weak due to its perturbative nature, although a strong nonlinear response is of crucial importance to applications in optical limiting and switching. Here we demonstrate experimentally and theoretically an extremely efficient scheme of excited-state absorption by charge transfer between donor and acceptor materials as a method to enhance the nonlinear absorption by orders of magnitude. With this idea, we demonstrate a strong excited-state absorption (ESA) in reduced graphene oxide that otherwise shows an increased transparency at high fluence and enhancement of ESA by one order of magnitude in graphene oxide by attaching gold nanoparticles (Au NP) in the tandem configuration that acts as an efficient charge-transfer pair when excited at the plasmonic wavelength. To explain the unprecedented enhancement, we develop a five-level rate-equation model based on the charge transfer between the two materials and numerically simulate the results. To understand the correlation of interfacial charge transfer with the concentration and type of the functional ligands attached to the graphene oxide sheet, we investigate the Au-NP—graphene oxide interface with various possible ligand configurations from first-principles calcu- lations. By using the strong ESA of our hybrid materials, we fabricate liquid cell-based high-performance optical limiters with important device parameters better than that of the benchmark optical limiters.
... In addition, owing to the more metallic nature of Se, the electrical conductivity is improved after the Se atom doping into the frameworks of MoS 2 . Se-doped MoS 2 nanosheets with superior electrical conductivity could efficiently transfer the photo-generated electrons when excited by the fs pulsed laser at 800 nm, which could suppress the charge recombination and produce a charge-separated excited state, giving rise to strong and ultrafast NLO performance [37,38]. The imaginary part of the nonlinear third-order susceptibility Imχ (3) is linked with β by Imχ (3) =[10 −7 cλn 2 /96π 2 ]β (cm W −1 ) [21], where c stands for light speed in vacuum, λ and n represent the wavelength of the laser pulse and the refractive index, respectively. ...
Article
Full-text available
Enhanced nonlinear optical (NLO) performance was observed in Se-doped MoS2 nanosheets synthesized through a facile annealing process. Se-doped MoS2 nanosheets with large saturable intensity and high modulation depth generated stable passively Q-switched fiber laser pulses at 1559 nm. In comparison with the Q-switched fiber laser utilizing the pristine MoS2 nanosheets as a saturable absorber, Se-doped MoS2 nanosheets-based passively Q-switching operation could be conducted at a lower threshold power of 50 mW, wider range of repetition rate from 28.97 to 130 kHz and higher SNR of 56 dB. More importantly, the shortest pulse duration of 1.502 μs was realized; the output power and pulse energy reached to 17.2 mW and 133.07 nJ, respectively. These results indicate that tailoring the chemical composition of optical nanomaterials by introducing dopant is a feasible method to improve the NLO response and realize excellently ultrafast pulse generation.
... Researches have shown that a suitable and reliable method for improving the NLO properties of GO is its combination with materials that have nonlinear optical properties. Therefore, many different compound materials with GO basis were synthesized and studied [19][20][21][22][23][24][25]. Ag 2 S quantum dots (QDs) has also shown many capabilities in different works [26][27][28][29]. ...
Article
Nonlinear optical properties including size and sign of nonlinear refractive index and nonlinear absorption coefficient of Graphene Oxide (GO), Ag2S@ZnS quantum dots and GO-Ag2S@ZnS were investigated using a Z-scan technique by laser diode with 532 nm wavelength. Third-order susceptibility of the compounds was calculated and compared with the reported values. By comparing the nonlinear optical (NLO) properties of GO and the mixture of GO-Ag2S@ZnS, it was observed that the NLO properties of GO were increased using simply mixing with Ag2S@ZnS quantum dots. It was also observed that with increase of sonication time, the NLO properties of the mixture increased accordingly.
... Progress in high power ultrashort pulse lasers has opened new frontiers in science and technology of light-matter interactions [453]. The availability of high repetition femtosecond lasers, precise fast scanning stages and galvano mirrors allows for an increasing number of the applications. ...
Article
Full-text available
The interaction of intense femtosecond laser pulses with transparent materials is a topic that has caused great interest of scientists over the past two decades. It will continue to be a fascinating field in the coming years. This is because many challenging fundamental problems have not been solved, especially concerning the interaction of strong, ultra-short electromagnetic pulses with matter, and also because potential advanced technologies will emerge due to the impressive capability of the intense femtosecond laser to create new material structures and hence functionalities. When femtosecond laser interacts with matter, a large amount of energy will be released during an ultra-short period of time, resulting in extremely high energy intensity. This opens the avenue to explore new light-matter interacting phenomena, investigate the details of the dynamical processes of the light-matter interaction, and fabricate various integrated micro-devices. In recent years we have witnessed exciting development in understanding and applying femtosecond laser induced phenomena in transparent materials. The interaction of femtosecond laser pulses with transparent materials relies on non-equilibrium process with photon beams and this provides new access to create materials and micro-devices that cannot be obtained by other means. Understanding of the physical mechanisms of many induced phenomena is extremely challenging. The aim of this review is to present a critical overview of the current state of the art in studying femtosecond laser induced various phenomena in transparent materials, including their physical and chemical mechanisms, the applications and limitations as well as the future research trends. The first part of the review presents the basics of femtosecond laser systems, important parameters influencing the femtosecond laser interaction with transparent materials, and a brief description of various energy transfer processes in materials during femtosecond laser irradiation. The second part will give an account on various phenomena such as multiphoton excited upconversion luminescence, long lasting phosphorescence, formation of color centers, valence state change, precipitation of nanoparticles and nanocrystals, microvoids, polarization-dependent and periodic surface structures, refractive index change, polymerization and air-bubble formation. The third part describes recently observed "anomalous" phenomena such as induced birefringence, nanogratings, nanovoid arrays, migration of ions, nonreciprocal photosensitivity, high pressure crystalline phase, and their underlying mechanisms, and their potential prospects as a new tool for photonic technology development. The final part points out the major challenges and future research trends in this promising field.
Article
Y2O3: Yb, Er nanophosphors were synthesized by sol-gel approach and preliminary characterization confirms the existence of lanthanide dopants and the host material in the appropriate ratio with nanosphere-like morphology. Linear absorption displays visible and NIR absorption regions due to the sub-bandgap states involved in f-f transitions of Er- Yb ions. PL study shows more intense red emissions than blue and green emissions due to the combination of energy transfer and cross-relaxation process in Er ions. Wavelength-dependent nonlinear optical response of Y2O3: Yb, Er was examined by adapting the intensity-dependent Z-scan technique (open aperture) using nano pulsed Nd: YAG laser. Remarkably Y2O3: Yb, Er nanophosphors show reverse saturable absorption ascribed due to the two-photon absorption and two/three-photon absorption at 532 nm and 1064 nm respectively. The nonlinear absorption coefficient reliant on the intensity of the laser unambiguously demonstrates the presence of a sequential multi-photon absorption process. The results from the Z-scan experiment demonstrate the influence of the sub-bandgap energy states of the Y2O3 matrix due to the Yb and Er dopants in the excited state absorption behaviour. Upconversion integrated optical limiting of Y2O3: Yb, Er nanophosphors provide a potential origin for designing high-performance broadband solid-state optical limiters for laser protection devices.
Article
Full-text available
Laser‐induced graphene (LIG) has attracted extensive attention owing to its facile preparation of graphene and direct engraving patterns for devices. Various applications are demonstrated such as sensors, supercapacitors, electrocatalysis, batteries, antimicrobial, oil and water separation, solar cells, and heaters. In recent years, doping has been employed as a significant strategy to modulate the properties of LIG and thereby improve the performance of LIG devices. Due to the patternable manufacture, controllable morphologies, and the synergistic effect of doped atoms and graphene, the doped LIG devices exhibit a high sensitivity of sensing, pseudocapacitance performance, and biological antibacterial. This paper reviews the latest novel research progress of heteroatom and nanoparticles doped LIG in synthesis, properties, and applications. The fabrications of LIG and typical doping approaches are presented. Special attention is paid to two doping processes of LIG: the one‐step laser irradiation method and the two‐step laser modification consisting of deposition, drop‐casting, and duplicated laser pyrolysis. Doped LIG applications with improved performance are mainly highlighted. Taking advantage of doped LIG's properties and device performances will provide excellent opportunities for developing artificial intelligence, data storage, energy, health, and environmental applications.
Article
The development of effective laser protectors to protect the human eyes and all optical and photoelectric sensors from temporary or permanent damage caused by laser beams, which is both of...
Article
Plasmonic nanocomposites have been extensively studied for over 3 decades. According to early theoretical studies, a large enhancement of nonlinear response has been predicted. Nonetheless, the promised enhancement of coherent or Kerr‐type nonlinearities incurs major limitations related to strong absorption and saturation effects. Accordingly, diffraction‐limited interactions and long‐scale propagation in ultrafast timescales are undermined despite nanoscale‐localized electronic field enhancement. Seemingly only nanometric devices operating at low intensity regimes are benefitted from the foresaid effect. Nonetheless, numerous studies have still exploited configurable properties of the nonlinear response of plasmonic nanocomposites, such as nonlinear absorption, high‐order nonlinearities, and diffusive nonlinearities for the development of novel processes within the framework of nonlinear wave propagation described by effective medium properties. In this review, the most recent developments on the understanding of the nonlinear response of metals and plasmonic nanocomposites in various temporal regimes are presented. Furthermore, a synthesis of their experimentally determined third‐order properties obtained by various experimental techniques, along with practical considerations, is provided. Computational models used for the formulation of nonlinear wave propagation in plasmonic nanocomposites are subsequently presented, corresponding to applicable concepts. Most recent related applications are concisely summarized, indicating the directions of increasing interest in the field, and outlining shortcomings.
Article
Full-text available
Laser photoreduction of metal ions onto graphene oxide (GO) is a facile, environmentally friendly method to produce functional metal-GO nanocomposites for a variety of applications. This work compares Au-GO nanocomposites prepared by photoreduction of [AuCl4]– in aqueous GO solution using laser pulses of nanosecond (ns) and femtosecond (fs) duration. The presence of GO significantly accelerates the [AuCl4]– photoreduction rate, with a more pronounced effect using ns laser pulses. This difference is rationalized in terms of the stronger interaction of the 532 nm laser wavelength and long pulse duration with the GO. Both the ns and fs lasers produce significant yields of sub-4 nm Au nanoparticles attached to GO, albeit with different size distributions: a broad 5.8 ± 1.9 nm distribution for the ns laser and two distinct distributions of 3.5±0.8 and 10.1±1.4 nm for the fs laser. Despite these differences, both Au-GO nanocomposites had the same high catalytic activity towards p-nitrophenol reduction as compared to unsupported 4–5 nm Au nanoparticles. These results point to the key role of GO photoexcitation in catalyzing metal ion reduction and indicate that both ns and fs lasers are suitable for producing functional metal-GO nanocomposites.
Article
Motivated by the accomplishment of carbon nano tubes (CNTs), graphene and graphene oxide (GO) have been widely investigated in the previous quite a long while as an innovative medication nanocarrier for the stacking of a variety of therapeutics as well as anti-cancer medications, ineffectively dissolvable medications, anti-microbials, antibodies, peptides, DNA, RNA and genes. The greatly huge surface region of graphene, with each molecule uncovered on its two sides, is took into consideration ultra-high medication stacking effectiveness. Graphene and GO have been widely investigated by way of the absolute greatest encouraging biomaterials for biomedical applications as they have exceptional qualities: two-dimensional planar structure, substantial surface territory, chemical and mechanical constancy, sublime conductivity and great biocompatibility. Because of these special qualities GO applications bring cutting edge medicate transports frameworks and transports of a wide scope of therapeutics. In this review we discuss the latest advances and improvements in the uses of graphene and GO for drug transport and nanomedicine. Initially, we describe what is graphene and graphene oxide then after by the qualities of GO as a drug transport then we discuss the utilization of GO in drug transport applications, Targeted drug transport, transport of anticancer medications, chemical control medicine releasee, Co-transport of different medications, Comparison of GO with CNTs, Nano graphene for drug transport and in the last we discuss about the Graphene toxicity. At the end we conclude this review with a conclusion of current expansion and the potential outlook for the future.
Article
The widespread application of laser devices requires development of new protections against light pulses of high intensity. This problem is relevant because of the danger of hitting the civil aviation pilots with bright and powerful radiation originating from the laser sources which are widely used in the everyday life. Therefore, this work is devoted to continuing our research on a new class of macroheterocyclic compounds – thermally and chemically stable J-type phthalocyanine dimers as potential nonlinear absorbers for optical limiting technology. The dimeric complexes of magnesium (1a) and zinc (1b) were covalently bonded to single-walled carbon nanotubes (SWCNTs) to improve the overall characteristics of the potential optical limiters 2a,b as compared to the previously studied corresponding dyes in solutions. The conjugates obtained were investigated using atomic force microscopy (AFM), as well as Raman and IR spectroscopy to confirm formation of the covalent binding of phthalocyanine macrocycles with the carbon surface. Open-aperture Z-scan and a fixed limiter location experiments have demonstrated low values of the limiting threshold and high degree of attenuation of the input laser radiation with the pulses duration located in the nanosecond range.
Article
Gold nanorod (GNR) and reduced graphene oxide (rGO) hybrids are synthesized using photochemical method based on femtosecond laser ablation without the usage of strong chemical reducing agents. The products are characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The formed GNR are well located on the surface of rGO sheets. By adjusting the laser ablation time, the aspect ratio and optical properties of GNR can be well controlled. The produced nanocomposites exhibited an excellent near-infrared (NIR) photothermal performance with a photothermal conversion efficiency of 77.8%, suggesting that the hybrids have large potential as agents in photothermal therapy.
Article
A novel three-dimensional ordered hollow spherical Sn ⁴⁺ doped TiO 2 material with ZnO quantum dot sensitization (ZnO [email protected] 2 ) was synthesized by a simple colloidal template method. The characterization results indicate that the crystal phase of the prepared composite could be controlled by modifying the loading of ZnO QDs under the synergistic action of ZnO QDs and Sn ⁴⁺ while maintaining the favorable three-dimensional ordered hollow sphere structure. Based on diffuse reflectance and fluorescence spectroscopy, ZnO QDs provide multiple migration pathways for photogenerated carriers, effectively inhibiting the recombination of photogenerated electron–hole pairs. And the photocatalytic experiments show that the photocatalyst ZnO [email protected] 2 has significantly improved photocatalytic performance than pure TiO 2 . Simultaneously, the optimized results show that 2.0 ZnO [email protected] 2 has the best degradation rate and photocatalytic activity. In summary, this work provides a new approach for the synthesis of multi-morphological mixed phase TiO 2 photocatalysts for photocatalytic applications.
Article
Full-text available
Reduced graphene oxide (rGO) decorated with silver nanoparticles (Ag NPs) is synthesized by femtosecond laser ablation in solution method. The nonlinear optical properties of both rGO and Ag NPs/rGO are measured using a femtosecond laser Z-scan technique. The results reveal that both the nonlinear absorption and nonlinear refraction in the hybrid are enhanced due to the interaction of the energy state of Ag NPs. The composite shows a saturation intensity 18.5 MW/cm2 and boosts the nonlinear refraction as large as 2~3 times of that of rGO reaching to −1.1 × 10⁻¹² m²/W. The enhancement of the saturable absorption might be caused by the further bleaching the valence band of rGO due to the transfer of the light excited carriers from graphene to the metal state of the NPs. The slow relaxation of the excited carriers to the ground state of rGO will also cause the increase of the carrier density and thereby result in the enhancement of the nonlinear refractive index of the material.
Article
Graphene is being claimed to be an amazing material which can be made from a layer of carbon one-atom thick. It currently appears to be the strongest material in the world. Yet is completely flexible and more conductive than copper. All of these are just hypothetical at this point, but could be real and all could be incredible. In view of these potentials, research on the potential for application of graphene continues to expand internationally in terms of new products and innovative production techniques. It is clear from the number of publications being generated internationally that the research effort has multiplied manifold over the last 10 years involving more than 20 countries of the world. Internationally published papers indicate that these topics include a growing number of products which are based on integrating graphene across a range of applications. These applications include developments of products including consumer electronic devices, wearables, flexible RF devices, supercapacitors, conductive inks, sensors and coatings. This article gives detailed statistics in terms of R & D publications internationally over the past 10 years and demonstrates the rate of growth of interest on various aspects of Graphene and its practical applications.
Article
In order to construct reduced graphene oxide (RGO) contained 3D ordered chiral architecture and exploit the anisotropic properties of RGO to develop functional soft matter, a brand new nanosurfactant which is two-dimensional charged zirconium phosphate (CZ) nanoplatelet is firstly designed and applied to disperse RGO in liquid phase and ordered soft matter. The rheological behavior analysis shows the RGO suspensions can change from unhomogeneous non-newtonian nanofluids to homogeneous newtonian nanofluids after being exfoliated by CZ nanoplatelets. Absorption spectra indicate that the dispersion stability of RGO in liquid phase can be gradually improved with the increase of CZ content. RGO is effectively dispersed in a type of ordered soft matter (chiral nematic liquid crystals, CNLCs) when the mass ratio between CZ and RGO reaches 8. X-ray diffraction results prove that the interlayer spacing of CNLCs has been reduced with the increase of RGO content. Raman spectra confirm the characteristic bands of CZ-RGO-CNLC composites and the physical coupling among CZ, RGO and CNLC. The ternary CZ-RGO-CNLC composites possess chiral helical configuration and Bragg selective reflection characteristic. The driving electric intensity and the saturated electric intensity of the ternary CZ-RGO-CNLC composites with 0.1 wt% RGO addition can be significantly reduced compared with single-component CNLCs.
Article
Layered materials, such as graphene, transition metal dichalcogenides and black phosphorene, have been established rapidly as intriguing building blocks for optoelectronic devices. Here, we introduce highly polarization sensitive, broadband, and high-temperature-operation photodetectors based on multilayer germanium sulfide (GeS). The GeS photodetector shows a high photoresponsivity of about 6.8 × 103 A/W, an extremely high specific detectivity of 5.6 × 1014 Jones, and broad spectral response in the wavelength range of 300-800 nm. More importantly, the GeS photodetector has high polarization sensitivity to incident linearly polarized light, which provides another degree of freedom for photodetectors. Tremendously enhanced photoresponsivity is observed with temperature increase, and high responsivity is achievable at least up to 423 K. The establish of larger photoinduced reduction of Schottky barrier height will be significant for the investigation of photoresponse mechanism of 2D layered materials based photodetectors. These attributes of high photocurrent generation in a wide temperature range, broad spectral response, and polarization sensitivity coupled with environmental stability indicate that the proposed GeS photodetector is very suitable for optoelectronic applications.
Chapter
One of the most attractive characteristics of nanosheets and nanosheet-based materials, when being considered as optical materials, is their high anisotropy. Therefore, nanosheets and nanosheet-based materials are suitable as optical materials that require an anisotropic optical response. An essential requirement for the use of a nanosheet as an optical material is the ability to obtain low light-scattering nanosheet-based solid materials. In the first part of this chapter, the preparation techniques for obtaining low light-scattering nanosheet-based solid materials, such as Langmuir–Blodgett, filtration-based, and index matching techniques, are introduced. Then, studies on the optical functionalities of various kinds of nanosheet-based solid materials, such as superlattice and plasmonic nanostructures, are reviewed. Furthermore, efficient nonlinear optical nanosheet-based materials, in which specific characteristics of the nanosheets are ingeniously used, will be discussed.
Article
Low-dimensional (LD) materials demonstrate intriguing optical properties, which lead to applications in diverse fields, such as photonics, biomedicine and energy. Due to modulation of electronic structure by the reduced structural dimensionality, LD versions of metal, semiconductor and topological insulators (TIs) at the same time bear distinct nonlinear optical (NLO) properties as compared with their bulk counterparts. Their interaction with short pulse laser excitation exhibits a strong nonlinear character manifested by NLO absorption, giving rise to optical limiting or saturated absorption associated with excited state absorption and Pauli blocking in different materials. In particular, the saturable absorption of these emerging LD materials including two-dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q-switching and mode-locking ultra-short pulse generation across the visible, near infrared and middle infrared wavelength regions. Beside the large operation bandwidth, these ultrafast photonics applications are especially benefit from the high recovery rate as well as the facile processibility of these LD materials. The prominent NLO response of these LD materials have also provided new avenues for the development of novel NLO and photonics devices for all-optical control as well as optical circuits beyond ultrafast lasers.
Article
Graphene and its functionalized derivatives are unique and multifaceted novel materials with a wide range of applications in chemistry, healthcare, and optoelectronic engineering. 3D graphene materials exhibit several advantages over 2D (monolayer) graphene for a variety of devices applications. Here a novel and effective room temperature technique is introduced to convert an aqueous graphene oxide solution into a reduced graphene oxide gel with tunable physical and chemical properties comparable to a monolayer graphene sheet, without the need for any additives or chemical agents. The femtogel is synthesized by exposing an ultrahigh concentration graphene oxide solution with single-layer flakes to high intensity femtosecond laser pulses. The femtosecond laser beam is focused on the air/aqueous solution interface to enhance the vaporization of functional groups and water, enabling femtogel formation. By controlling the pulsed laser intensity, beam focal parameters, and pulse duration, it is possible to produce several milliliters of femtogel in as little as 8 min. Through initial optimization of the irradiation parameters, a thin film is produced from a femtogel that demonstrates a surface roughness less than 6 nm, and more than 95% reduction in OH absorbance, as compared to a thin film produced from the unexposed graphene oxide solution.
Article
Full-text available
A facile photochemical approach to prepare nitrogen doped graphene quantum dots (NGQDs) has been presented. NGQDs exhibit strong photofluorescence (PL) in both colloid and solid states. Abnormal emission behavior is observed and the mechanism is discussed. The unique solid-state PL of NGQDs inspires new ideas for novel applications in micro-solid devices.
Article
Full-text available
Hierarchical SnO2@rGO nanostructures with superhigh surface areas are synthesized via a simple redox reaction between Sn2+ ions and graphene oxide (GO) nanosheets under microwave irradiation. XRD, SEM, TEM, XPS, TG-DTA and N2 adsorption–desorption are used to characterize the compositions and microstructures of the SnO2@rGO samples obtained. The SnO2@rGO nanostructures are used as gas-sensing and electroactive materials to evaluate their property–microstructure relationship. The results show that SnO2 nanoparticles (NPs) with particle sizes of 3–5 nm are uniformly anchored on the surfaces of reduced graphene oxide (rGO) nanosheets through a heteronucleation and growth process. The as-obtained SnO2@rGO sample with a hierarchically sesame cake-like microstructure and a superhigh specific surface area of 2110.9 m2 g−1 consists of 92 mass% SnO2 NPs and 8 mass% rGO nanosheets. The sensitivity of the SnO2@rGO sensor upon exposure to 10 ppm H2S is up to 78 at the optimal operating temperature of 100 °C, and its response time is as short as 7 s. Compared with SnO2 nanocrystals (5–10 nm), the hierarchical SnO2@rGO nanostructures have enhanced gas-sensing behaviors (i.e., high sensitivity, rapid response and good selectivity). The SnO2@rGO nanostructures also show excellent electroactivity in detecting sunset yellow (SY) in 0.1 M phosphate buffer solution (pH = 2.0). The enhancement in gas-sensing and electroactive performance is mainly attributed to the unique hierarchical microstructure, high surface areas and the synergistic effect of SnO2 NPs and rGO nanosheets.
Article
Full-text available
We demonstrate the synthesis as well as the optical characterization of core-shell nanowires. The wires consist of a potassium niobate (KNbO3) core and a gold shell. The nonlinear optical properties of the core are combined with the plasmonic resonance of the shell and offer an enhanced optical signal in the near infrared spectral range. We compare two different functionalization schemes of the core material prior to the shell growth process: silanization and polyelectrolyte. We show that the latter leads to a smoother and complete core-shell nanostructure and an easier-to-use synthesis process. A Mie-theory based theoretical approach is presented to model the enhanced second-harmonic generated (SHG) signal of the core-shell wires, illustrating the influence of the fabrication-induced varying geometrical factors of wire radius and shell thickness. A spectroscopic measurement on a core-shell nanowire shows a strong localized surface plasmon resonance close to 900 nm, which matches with the SHG resonance obtained from nonlinear optical experiments with the same nanowire. According to the simulation, this corresponds to a wire radius of 35 nm and a shell thickness of 7.5 nm. By comparing SHG signals measured from an uncoated nanowire and the coated one, we obtain a 250 times enhancement factor. This is less than the calculated enhancement, which considers a cylindrical nanowire with a perfectly smooth shell. Thus, we explain this discrepancy mainly with the roughness of the synthesized gold shell.
Article
Full-text available
Ensuring clean and efficient energy sources is one of the biggest challenges that people face in the 21st century. Among the proposed clean energy sources, fuel cells, such as proton exchange membrane fuel cells (PEMFC), direct methanol fuel cells (DMFC), direct formic acid fuel cells (DFAFC) have been considered a class of the most promising power sources with high energy density and high efficiency. The main reactions in a fuel cell include the fuel oxidation on anode and the oxygen reduction on cathode. Among the metal catalysts for anode and cathode reactions, platinum (Pt) exhibits the highest electrocatalytic activities for electro-oxidation of small organic fuels on the anode and the oxygen reduction on the cathode. However, with Pt alone as catalyst, several obvious disadvantages largely limit its application in fuel cells.
Article
Full-text available
A direct and facile method for micro-landscaping of Ag nanoparticles on reduced graphene oxide (rGO) is presented. This method employs a focused laser beam to achieve local reduction of Ag(+) ions to Ag NPs by laser irradiation on a GO film that is submerged in AgNO3 solution. Using this method, the Ag nanoparticles can be directly anchored on a rGO film, creating a microlandscape of Ag nanoparticles on the rGO film. In addition, varying the intensity of the laser beam can control the shapes, sizes and distributions of Ag nanoparticles. The resulting hybrid materials exhibit surface enhanced Raman scattering of up to 16 times depending on the size and number density of silver nanoparticles. In addition, the hybrid Ag-rGO material shows superior photoresponse when compared to rGO.
Article
Full-text available
Programmable N-doping and simultaneous reduction of graphine oxide (GO) by femtosecond laser direct writing in NH3 atmosphere is presented. The unique laser-mediated programmable doping permits complex micropatterns of N-doped graphene, and thus holds great promise for the fabrication and integration of graphene-based devices. N-type transistor behavior is observed in the post-fabricated field-effect transistors.
Article
Full-text available
A facile and novel preparation strategy based on electrochemical techniques for the fabrication of electrodeposited graphene (EGR) and zinc oxide (ZnO) nanocomposite was developed. The morphology and structure of the EGR-based nanocomposite were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (XPS) and Raman spectroscopy. Meanwhile, the electrochemical performance of the nanocomposite was demonstrated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect of EGR and ZnO nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (AC) and phenacetin (PCT) was successfully fabricated. The linearity ranged from 0.02 to 10 μM for AC and 0.06 to 10 μM for PCT with high sensitivities of 54 295.82 μA mM(-1) cm(2) for AC and 21 344.66 μA mM(-1) cm(2) for PCT, respectively. Moreover, the practical applicability was validated to be reliable and desirable in pharmaceutical detections. The excellent results showed the promise of the proposed preparation strategy of EGR-transition metal oxide nanocomposite in the field of electroanalytical chemistry.
Article
Full-text available
Carbon nanoparticles (CNPs), hollow CNPs, nanodiamonds, and hybrid graphene spheres (HGSPs) are produced by using fs laser ablation in solution. These carbon nanostructures emit tunable photoluminescence and two-photon luminescence. The photoinduced layer-by-layer assembly of graphene nanosheets is observed to form HGSPs with tailored broadly-ranged sizes for the first time.
Article
Full-text available
We present the mechanism and performance of optical limiting (OL) in hydrogen exfoliated graphene (HEG), functionalized HEG (f-HEG) and its metal hybrids. At the wavelengths used, the mechanism of nonlinear absorption (NLA) involves two-photon absorption and excited state absorption in the nanosecond excitation regime, and saturable absorption in combination with two-photon absorption in the femtosecond (ultrafast) excitation regime. The role of defects in the OL performance of HEG and f-HEG is investigated with the help of their Raman spectra. OL efficiency of f-HEG is found to improve with Pt and Pd nanoparticle decoration due to an enhanced NLA, which arises mainly from interband transitions between the d band and the s–p conduction band in the metal NPs, and charge transfer between f-HEG and metal NPs. Thermally induced light scattering is negligible in these water dispersed systems.
Article
Full-text available
Highly loaded and ultrafine Pd nanoparticles were supported on graphene oxide (PdNPs-GO) via an in situ, simple and clean strategy on the basis of the direct redox reaction between Pd(OAc)2 and GO. A highly sensitive biosensor was developed for the detection of glucose based on the electrode modified with PdNPs-electrochemically reduced GO (PdNPs-ERGO). The glucose biosensor shows a wide linear range, low detection limit, good reproducibility and acceptable stability, providing a biocompatible platform for biosensing and biocatalysis.
Article
Full-text available
We demonstrate an approach toward the design of starburst C60-keto-DPAF assembly by applying a starburst macromolecular configuration with C60 as the core center, which is encapsulated by multiple bulky groups leading to the increase of intermolecular separation and aggregation barrier. Molecular compositions of the resulting C60(>DPAF-C9)2 triad and C60(>DPAF-C9)4 pentads were clearly confirmed by MALDI-MS (positive ion) detection of protonated molecular mass ions. Both C60(>DPAF-C9)22 and C60(>DPAF-C9)4 (structural isomers, 3a and 3b) exhibited nonlinear optical transmittance reduction responses in the femtosecond (fs) region with a lower transmittance value for the latter at the high laser power above 80 GW cm−2. This was attributed to the larger fs 2PA cross-section values of 3a and 3b than that of 2 at the same concentration and, apparently, correlated to a higher number of DPAF-C9 subunits in the structure of 3. As the concentration was decreased to 10−4 M, a clear monotonous increase of the σ2 value change (Δσ2) from 13.9, 33.2, to 48.1 and 68.2 × 10−48 cm4 s photon−1 molecule−1 (or 6820 GM for the latter) for the structural variation from the monoadduct 1, bisadduct 2, to tetraadducts 3b and 3a, respectively, was observed. We interpreted the concentration-dependent phenomenon as being due to the high tendency of fullerene-DPAF chromophores to form nanoscale aggregates at concentrations above 10−3 M. We also proposed that starburst structures, as exemplified by C60(>DPAF-C9)4, in a multipolar arrangement resembling encapsulation of C60 by DPAF-C9 pendants, provide a useful means to increase the degree of molecular dispersion and maintain high nonlinear optical efficiency.
Article
Full-text available
The development of new tools and devices to aid in treating cancer is a hot topic in biomedical research. The practice of using heat (hyperthermia) to treat cancerous lesions has a long history dating back to ancient Greece. With deeper knowledge of the factors that cause cancer and the transmissive window of cells and tissues in the near-infrared region of the electromagnetic spectrum, hyperthermia applications have been able to incorporate the use of lasers. Photothermal therapy has been introduced as a selective and noninvasive treatment for cancer, in which exogenous photothermal agents are exploited to achieve the selective destruction of cancer cells. In this manuscript, we propose applications of barium titanate core–gold shell nanoparticles for hyperthermia treatment against cancer cells. We explored the effect of increasing concentrations of these nanoshells (0–100 μg/mL) on human neuroblastoma SH-SY5Y cells, testing the internalization and intrinsic toxicity and validating the hyperthermic functionality of the particles through near infrared (NIR) laser-induced thermoablation experiments. No significant changes were observed in cell viability up to nanoparticle concentrations of 50 μg/mL. Experiments upon stimulation with an NIR laser revealed the ability of the nanoshells to destroy human neuroblastoma cells. On the basis of these findings, barium titanate core–gold shell nanoparticles resulted in being suitable for hyperthermia treatment, and our results represent a promising first step for subsequent investigations on their applicability in clinical practice.
Article
Full-text available
Compared with the conventional deposition techniques used for the epitaxial growth of metallic structures on a bulk substrate, wet-chemical synthesis based on the dispersible template offers several advantages, including relatively low cost, high throughput, and the capability to prepare metal nanostructures with controllable size and morphology. Here we demonstrate that the solution-processable two-dimensional MoS(2) nanosheet can be used to direct the epitaxial growth of Pd, Pt and Ag nanostructures at ambient conditions. These nanostructures show the major (111) and (101) orientations on the MoS(2)(001) surface. Importantly, the Pt-MoS(2) hybrid nanomaterials exhibit much higher electrocatalytic activity towards the hydrogen evolution reaction compared with the commercial Pt catalysts with the same Pt loading. We believe that nanosheet-templated epitaxial growth of nanostructures via wet-chemical reaction is a promising strategy towards the facile and high-yield production of novel functional materials.
Article
Full-text available
Under intense laser excitation, thin films and suspensions of graphite and its nanostructure, including carbon black, nanotubes, few-layer graphenes and graphene oxides, exhibit induced transparency due to saturable absorption. This switches to optical limiting only at very high fluences when induced breakdown gives rise to microbubbles and microplasmas that causes nonlinear scattering. Here, we show that dispersed graphenes, in contrast, can exhibit broadband nonlinear optical absorption at fluences well below this damage threshold with a strong matrix effect. We obtained, for nanosecond visible and near-infrared pulses, a new benchmark for optical energy-limiting onset of 10 mJ cm-2 for a linear transmittance of 70%, with excellent output clamping in both heavy-atom solvents and polymer film matrices. Nanosecond pump-probe spectroscopy in chlorobenzene reveals that the nanographene domains switch from the usual broadband photo-induced bleaching to a novel reverse saturable absorption mechanism with increasing excitation densities across this threshold.
Article
Full-text available
Ein Charge-Transfer-Komplex zwischen Graphenoxid (GO) und dem Pyrenfarbstoff PNPB wurde durch einen einfachen Ionenaustauschprozess hergestellt. Die hochspezifischen Wechselwirkungen des Komplexes mit DNA (siehe Schema) ermöglichen die selektive und schnelle Detektion von DNA in Mischungen verschiedener Biomoleküle. Zudem zeigt er eine breitbandige optische Leistungsbegrenzung.
Article
Full-text available
We report on the synthesis of nanocrystalline zirconia in liquid using femtosecond laser ablation. Nanocrystalline cubic zirconia has been prepared by femtosecond laser ablation of zirconium in ammonia, while nanocrystalline tetragonal and monoclinic zirconia was synthesized in water. The physical and chemical mechanisms of the formation of nanocrystalline metastable zirconia are discussed. The intrinsic properties of femtosecond laser ablation in liquid and OH−1 may be responsible for the synthesis of cubic zirconia. It is suggested that the femtosecond laser pulse can create higher temperature and pressure conditions at a localized area in the liquid than the nanosecond laser pulse and the cooling is also faster in the femtosecond laser ablation process, which determined the difference between the products synthesized with femtosecond and nanosecond-pulsed laser ablation. KeywordsCubic zirconia–Ammonia–Femtosecond laser ablation–High temperature–Mechanism
Article
Metal nanoclusters consist of a few to few hundreds of atoms, and exhibit attractive molecular properties such as ultrasmall size, discrete energy levels and strong fluorescence. Although patterning of these clusters down to the micro- or nanoscale could lead to applications such as high-density data storage, it has been reported only for inorganic matrices. Here we present submicron-scale mask-free patterning of fluorescent silver nanoclusters in an organic matrix. The nanoclusters were produced by direct laser writing in poly(methacrylic acid) thin films, and exhibit a broadband emission at visible wavelengths with photostability that is superior to Rhodamine 6G dye. This fabrication method could open new opportunities for applications in nanophotonics like imaging, labeling, and metal ion sensing. We foresee that this method can be further applied to prepare other metal nanoclusters embedded in compositionally different polymer matrices.
Article
We detail a facile method for enhancing the Raman signals of as-grown graphene on Cu foils by depositing gold nanoislands (Au Nis) onto the surface of graphene. It is found that an enhancement of up to 49 fold in the graphene Raman signal has been achieved by depositing a 4 nm thick Au film. The enhancement is considered to be related to the coupling between graphene and the plasmon modes of Au Nis, as confirmed by the finite element simulations. The plasmonic effect of the Au/graphene/Cu hybrid platform leads to a strong absorption at the resonant wavelength whose position shifts from visible light (640 nm) to near-infrared (1085 nm) when the thickness of Au films is increased from 2 nm to 18 nm. Finally, we demonstrate that hybrid substrates are reliable surface-enhanced Raman scattering (SERS) systems, showing an enhancement factor of ∼10(6) for dye molecules Rhodamine B and Rhodamine 6G with uniform and stable response and a detection limit of as low as 0.1 nM for Sudan III and Sudan IV.
Article
N and S codoping of graphene is realized by a novel approach: covalent functionalization of graphene oxide using 2-aminothiophenol as a source of both N and S followed by thermal treatment. The resulting N- and S-codoped graphene has potential applications in high-performance lithium-ion batteries and as a metal-free catalyst for oxygen reduction reaction.
Article
The homogeneous attachment of metal-nanoparticles (metal-NPs) on pristine-graphene surface to construct pristine-graphene/metal-NPs hybrids is highly expected for application in many fields such as transparent electrodes and conductive composites. However, it remains a great challenge since the pristine-graphene is highly hydrophobic. Here, an environmentally friendly generic synthetic approach to large-scale pristine-graphene/metal-NPs hybrids is presented, by a combinatorial process of exfoliating expanded graphite in N-methyl pyrrolidone via sonication and centrifugation to achieve the pristine-graphene, and attaching pre-synthesized metal-NPs on the pristine-graphene in ethanol via van der Waals interactions between the metal-NPs and the pristine-graphene. Nanoparticles of different metals (such as Ag, Au, and Pd) with various morphologies (such as sphere, cube, plate, multi-angle, and spherical-particle assembling) can be homogeneously attached on the defect-free pristine-graphene with controlled packing densities. Both the pristine-graphene and the metal-NPs preserve their original intrinsic structures. The as-synthesized pristine-graphene/Ag-NPs hybrids show very high surface-enhanced Raman scattering activity due to the combined effects of large surface area of the pristine-graphene to adsorb more target molecules and the electromagnetic enhancement of the Ag-NPs. This large-scale synthesis of the pristine-graphene/metal-NPs hybrids with tunable shape and packing density of metal-NPs opens up opportunities for fundamental research and potential applications ranging from devices to transparent electrodes and conductive composites.
Article
We report on a simple and universal method for fabricating various kinds of metal and semiconductor (Si, Ge, Bi, and Cu) nanoparticle–glass composites by using metallic Al as a reducing agent in the raw materials of the glass batches. By taking advantage of the redox equilibrium that sets up between the Al reducing agent and various oxides, crystal nuclei such as Si and Ge atom clusters are already formed during the melt-quenching stage. During the subsequent heat-treatment stage, the nanoparticles grow on the nuclei by a process of diffusion. The nanoparticle size can be controlled by heat-treatment temperature and holding time. The fabricated nanoparticle–glass composites exhibit large third-order optical nonlinearities (χ3 up to 10–8 esu) and an ultrafast response time (within picoseconds), which makes them possible to manufacture ultrafast all-optical switches.
Article
Surfactant-free, size- and composition-controlled, unsupported, <5-nm, quantum-confined cobalt oxide nanoparticles with high electrocatalytic oxygen-evolution activity were synthesized by pulsed laser ablation in liquids. These crystalline Co3O4 nanoparticles have a turnover frequency per cobalt surface site among the highest ever reported for Co3O4 nanoparticle oxygen evolution catalysts in base and overpotentials competitive with the best electrodeposited cobalt oxides, with the advantage that they are suitable for mechanical deposition on photoanode materials and incorporation in integrated solar water-splitting devices.
Article
Carbon nanostructures are ideal substrates for functionalization with molecules since they consist of a single atomic layer giving rise to an extraordinary sensitivity to changes in their surrounding. The functionalization opens a new research field of hybrid nanostructures with tailored properties. Here, we present a microscopic view on the substrate-molecule interaction in the exemplary hybrid material consisting of graphene functionalized with perylene molecules. First experiments on similar systems have been recently realized illustrating an extremely efficient transfer of excitation energy from adsorbed molecules to the carbon substrate, a process with a large application potential for high-efficiency photovoltaic devices and biomedical imaging and sensing. So far, there has been no microscopically founded explanation for the observed energy transfer. Based on first-principle calculations, we have explicitly investigated the different transfer mechanisms revealing the crucial importance of Förster coupling. Due to the efficient Coulomb interaction in graphene, we obtain strong Förster rates in the range of 1/fs. We investigate its dependence on the substrate-molecule distance R and describe the impact of the momentum transfer q for an efficient energy transfer. Furthermore, we find that the Dexter transfer mechanism is negligibly small due to the vanishing overlap between the involved strongly localized orbital functions. The gained insights are applicable to a variety of carbon-based hybrid nanostructures.
Article
Few-layer graphene was transferred directly on top of Ag nanoparticles, and the coupling between graphene and localized surface plasmons (LSPs) of Ag nanoparticles was investigated. We found that the surface enhanced Raman spectroscopy of graphene was increased approximately 7-fold by near-fields of plasmonic Ag nanoparticles and the enhancement factor of graphene G peak increased with the particle size. Meanwhile, the LSP resonances of Ag nanoparticles exhibit a 10 nm redshift and a 13 nm broadening by the presence of graphene, which can be attributed to the coupling between the Ag LSPs and the graphene.
Article
Two-dimensional (2D) carbon allotropes, which are atomic thick layers made of network carbon atoms with hexagonal structured lattices, have been neglected until the direct investigation of mechanically exfoliated graphene by Novoselov et al. in 2004. Graphene is a 2D carbon allotrope with a unique structure of hexagonally arranged atoms that give it unparalleled electrical conductivity and carrier mobility, in addition to excellent mechanical flexibility and extremely high specific surface area. Graphene and its derivatives have been extensively studied for photovoltaic and photocatalytic applications due to their inherent nature to extract and transport charges from photon-absorbing semiconductors and conjugated polymers. Graphyne and graphdiyne, 2D carbon allotropes like graphene but containing not only doubly but also triply bonded carbon atoms, are predicted to possess intrinsic semiconductor bandgap and even more superior electrical properties than graphene. The current theoretical understanding and experimental status of graphyne and graphdiyne will be discussed in contrast of graphene, demonstrating those promising competitors to graphene in further lightening a new photoconversion. This review addresses the recent successes and current challenges of graphene, graphyne and graphdiyne, and provides insightful perspectives for the future applications of 2D carbon materials in photoelectric conversion and photocatalysis.
Article
Nearly monodispersed spherical silver nanoparticles (Ag NPs) were synthesized by using tannic acid (TA) both as reductant and stabilizer in a 30 oC water bath. The size of the as-prepared Ag NPs could be tuned in a range of 7-66 nm by changing the molar ratio of TA to silver nitrate and pH of the reaction solutions. UV-visible spectra, TEM observations and temporal evolution of the monomer concentrations for the reactions carried out at different experimental conditions showed that the improved size distribution and size tunability of the Ag NPs were mainly attributed to the use of TA which could promote the balance of nucleation and growth processes of the NPs effectively. Size of the Ag NPs was extendable up to 200 nm in one-pot fashion by the multi-injection approach. The size-dependent surface-enhanced Raman scattering (SERS) activity of the as-prepared Ag NPs was evaluated and the NPs with size around 100 nm were identified to show a maximum enhanced factor of 3.6X105. Moreover, the as-prepared TA-coated Ag NPs presented excellent colloidal stability compared to the conventional citrate-coated ones.
Article
A hybrid nonlinear optical component is described based on a Au–PAA metal–dielectric assembly, which exhibits unconventional self-defocusing and inverse optical switching behavior. This heteronanostructure realizes SPR-induced nonlinear optics that enable an ultra-low threshold and an extraordinarily high nonlinear response. Such an SPR-induced nonlinear response can be further mani­pulated by more complex host–guest configuration such as Au–PAA–Au–C60.
Article
In the present work, the role of the reaction temperatures on the morphologies of zinc oxide-reduced graphene oxide (ZnO-RGO) nanohybrids and their supercapacitive performance in two different aqueous electrolytes (1.0 M KCl and Na2SO4) were investigated. The ZnO-RGO nanohybrids were synthesized at two different temperatures (ca. 95 and 145 oC) by solvothermal method and labelled as ZnO-RGO-1 and ZnO-RGO-2 respectively. The structure and composition of ZnO-RGO nanohybrids were confirmed by means of X-ray diffraction, electron microscopes (scanning and transmission), X-ray photoelectron, photoluminescence and Raman spectroscopy. These results show that the temperature allows a good control on loading and morphology of ZnO nanoassemblies in ZnO-RGO nanohybrids and at elevated temperature of 145 oC, ZnO nanoassemblies break and get completely embedded into RGO matrices. The electrochemical performance of ZnO-RGO nanohybrids was examined by cyclic voltammograms (CVs), galvanostatic charge-discharge (chronopotentiometry) and electrochemical impedance spectroscopy (EIS) in 1.0 M KCl and Na2SO4 aqueous electrolytes respectively. Combining the EIS and zeta potential behavior, a direct link between the charge transfer resistance and electrical double layers is established which is responsible for excellent capacitive performance of ZnO-RGO-2. The ZnO-RGO-2 displays high specific capacitance (107.9 F/g, scan rate = 50 mVs-1) in 1.0 M KCl and exhibits merely 4.2% decay in specific capacitance values over 200 cycles.
Article
This tunable holographic sensor offers interrogation and a reporting transducer as well as an analyte-responsive hydrogel, rendering it label-free and reusable. A single 6 ns laser pulse is used to fabricate holographic sensors consisting of silver nanoparticles arranged periodically within a polymer film. The tunability of the sensor is demonstrated through pH sensing of artificial urine and validated through computational modeling.
Article
In this letter, we reported on the preparation and Li-ion battery anode application of ultrasmall Sn nanoparticles (~5 nm) embedded in nitrogen-doped porous carbon (denoted as 5-Sn/C). Pyrolysis of Sn(Salen) at 650 oC under Ar atmosphere was carried out to prepare N-doped porous 5-Sn/C composite with the BET specific surface area of 286.3 m2/g. The 5-Sn/C composite showed an initial discharge capacity of 1014 mAh/g and a capacity retention of 722 mAh/g after 200 cycles at the current density of 0.2 A/g. Furthermore, a reversible capacity of ~480 mAh/g was obtained at much higher current density of 5 A/g. The remarkable electrochemical performance of 5-Sn/C composite was attributed to the effective combination of ultrasmall Sn nanoparticles, uniform distribution, and porous carbon network structure, which simultaneously solved the major problems of pulverization, loss of electrical contact and particle aggregation facing Sn anode.
Article
Femtosecond laser ablation in solution (FLAS) is a unique and simple technique addressing the drawbacks of the conventional methods giving access to preparation of an ultra-broad spectrum of nanomaterials (NMs), since the NMs can be produced from nearly any solid materials and variable precursors in different solutions. After the energy injection in ultra-short time, extreme conditions with high temperature, high pressure and high cooling rate are created, under which many interesting phenomena occur, including nanomaterial formation. Characteristic advantages of this method are the applications in preparing a huge variety of NMs, the high purity of the products, and the in situ dispersion and functionalization of the as-prepared NMs in various solutions. This review is devoted to give a comprehensive understanding of the fundamental mechanisms of FLAS. A map of variable NMs prepared by FLAS and the promising applications are built up to pave the way for more future work in this field.
Article
Graphene nanosheet-supported ultrafine metal nanoparticles encapsulated by thin mesoporous SiO2 layers were prepared and used as robust catalysts with high catalytic activity and excellent high-temperature stability. The catalysts can be recycled and reused in many gas- and solution-phase reactions, and their high catalytic activity can be fully recovered by high-temperature regeneration, should they be deactivated by feedstock poisoning. In addition to the large surface area provided by the graphene support, the enhanced catalytic performance is also attributed to the mesoporous SiO2 layers, which not only stabilize the ultrafine metal nanoparticles, but also prevent the aggregation of the graphene nanosheets. The synthetic strategy can be extended to other metals, such as Pd and Ru, for preparing robust catalysts for various reactions.
Article
The rational design and controllable synthesis of strongly coupled inorganic/graphene hybrids represents a long-standing challenge to develop advanced catalysts and energy storage materials. Here, we report a simple sol-gel method towards creating ultra-dispersed TiO2 nanoparticles on graphene with an unprecedented degree of control based on the precise separation and manipulation of nanoparticle nucleated, grown, anchored and crystallized, and the reduction of graphene oxide (GO), respectively. The hybrid materials show ultra-dispersed small anatase nanoparticles (~ 5 nm), ultra-thin thickness (≤ 3 layers) and a high surface area of 229 m2/g, and exhibit a high specific capacity of 94 mAhg-1 at ~ 59 C, which is twice as that of mechanically mixed composites (41 mAhg-1), demonstrating the potential of strongly synergistic coupling effects for advanced functional systems.
Article
In this study, we report a facile bio-inspired method for large-scale preparation of highly dispersed Ag nanoparticles (NPs) on the surface of flexible reduced graphene oxide (rGO) paper with using dopamine (DA) both as a reductant and a surface modifier. Through the self-polymerization of dopamine, free-standing GO paper can be simultaneously reduced and modified with following in situ growth of monolayer Ag NPs on such a substrate. The spherical Ag NPs with an average diameter of 80 nm have a narrow size distribution and tunable cover density. Such a flexible rGO/Ag hybrid paper presents enhanced antibacterial activity against E. coli and a high active and sensitive SERS response toward Rhodamine 6G (R6G) molecules. The detection signals can be obtained while the R6G concentration is as low as to 10(-8) M. This work provides a simple strategy for large-scale fabrication of monolayer Ag NPs on flexible rGO paper as a portable antibacterial substrate and a potential SERS substrate for molecular detection applications.
Article
Silver has been utilized as a highly effective and broad-spectrum antibacterial agent in our daily life. However, low stability, poor long-term antibacterial efficiency, and potential environmental hazard of released Ag+ ions may limit its practical applications. Ag-graphene oxide (GO) nanocomposites have been reported to display highly enhanced antibacterial property, yet their stability and long-term antibacterial property have not been carefully investigated. Herein, we report the synthesis of Ag@Fe2O3-GO nanocomposites with tunable loading density up to full monolayer coverage by adopting a simple phase transfer method. Compared to Ag@Fe2O3, its GO composite shows enhanced stability with Ag+ releasing rate decreased by more than 2 times under dialysis condition. We discover that the presence of GO not only slows down Ag nanoparticle oxidation process, but also enables Ag+ ions recrystallization on GO surface. The Ag@Fe2O3-GO nanocomposites have shown better and long-term antibacterial property against both Gram-negative and Gram-positive bacteria than those of plain Ag and Ag@Fe2O3, displaying great potential as a promising long-term bactericide with suppressed environmental hazard.
Article
ZnO/reduced graphene oxide (RGO) nanocomposite with many zinc and oxygen vacancies, synthesized in a simple solvothermal reaction exhibits significant photocatalytic activity. Photoluminescence and electron paramagnetic resonance measurements indicate that the zinc vacancies and oxygen vacancies were generated on the ZnO surface, and were crucial to that photocatalytic behavior. The photodegradation of methylene orange was significantly reduced by the addition of h+ and OH scavengers. Both zinc and oxygen vacancies cause effective charge separation in the photodegradation of methylene orange, which markedly inhibits the recombination of charges. The advanced photocatalytic behavior of the ZnO/RGO composite is discussed in detail herein.
Article
Magnetic nanoparticles have several applications in biology and medicine, and recently, their use for optical applications is gaining substantial attention. In this paper we report a single step solution based synthesis of Ni–Ag and Fe–Ag bimetallic nanoparticles using hydrazine hydrate as the reducing agent. Structural, plasmonic, and nonlinear optical properties of the prepared nanoparticles are investigated using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV–Vis absorption spectroscopy and Z-scan. UV–Vis absorption studies reveal surface plasmon resonance (SPR) absorption at 400 nm which exhibits a small red shift with particle size due to scattering. XRD, EDS, HRTEM and SPR absorption confirm the presence of Ni–Ag and Fe–Ag nanoparticles. Nonlinear optical studies are carried out using the open aperture Z-scan technique employing 5 ns as well as 100 fs laser pulses. The nonlinearity is found to have contributions from absorption saturation, two-photon absorption, excited state absorption and induced thermal scattering of light. The effective nonlinear absorption in Ni–Ag and Fe–Ag nanoparticles is found to be higher than that of pristine Ag nanoparticles. The potential of these materials for optical limiting and photonic applications is discussed.
Article
Employing high-yield production of layered materials by liquid-phase exfoliation, molybdenum disulfide (MoS2) dispersions with large populations of single and few layers were prepared. Electron microscopy verified the high quality of the two-dimensional MoS2 nanostructures. Atomic force microscopy analysis revealed that ~39% of the MoS2 flakes had thicknesses of less than 5 nm. Linewidth and frequency difference of the E12g and A1g Raman modes confirmed the effective reduction of flake thicknesses from the bulk MoS2 to the dispersions. Ultrafast nonlinear optical (NLO) properties were investigated using open-aperture Z-scan technique. All experiments were performed using 100 fs pulses at 800 nm from a mode-locked Ti:Sapphire laser. The MoS2 nanosheets exhibited significant saturable absorption (SA) for the fs pulses, resulting in the third order NLO susceptibility Imχ(3)~10-15 esu, figure of merit~10-15 esu cm and free-carrier absorption cross section ~10-17 cm2. Induced free carrier density and the relaxation time were estimated to be ~1016 cm-3 and ~30 fs, respectively. At the same excitation condition, the MoS2 dispersions show better SA response than the graphene dispersions.
Article
Herein, a simple wet-chemical pathway has been demonstrated for the synthesis of silver nanoparticle conjugated reduced graphene oxide nanosheets where dimethylformamide (DMF) is judiciously employed as an efficient reducing agent. Altogether DMF reduces both silver nitrate (AgNO3) and graphene oxide (GO) in the reaction mixture. Additionally the presence of polyvinylpyrolidone (PVP) assists the nanophasic growth and homogeneous distribution of the plasmonic nanoparticle Ag (0). Reduction of graphene oxide and presence of aggregated Ag NPs on reduced graphene oxide (rGO) nanosheets are confirmed from various spectroscopic techniques. Finally the composite material has been exploited as an intriguing platform for surface enhanced Raman scattering (SERS) based selective detection of uranyl (UO22+) ion. The limit of detection has been achieved to be as low as 10 nM. Here the normal Raman spectral (NRS) band of uranyl acetate (UAc) at 838 cm-1 shifts to 714 cm-1 and 730 cm-1 as SERS bands for pH 5.0 and pH 12.0, respectively. This distinguished Raman shift of the symmetric streching mode for UO22+ ion is indicative of pronounced charge transfer (CT) effect. This CT effect even supports the higher sensitivity of the protocol towards UO22+ over other tested oxo-ions. It is anticipated that rGO nanosheets furnish a convenient compartment to favor the interaction between Ag NPs and UO22+ ion through proximity induced adsorption even at low concentration.
Article
A study was conducted to prepare organic-solution-processable functionalized-graphene (SPF Graphene) hybrid material with porphyrins and to demonstrate its photophysical properties including optical-limiting properties. The synthesis of the porphyrin-graphene nanohybrid, 5-4 (aminophenyl)-10, 15, 20-triphenyl porphyrin (TPP) and graphene oxide molecules covalently bonded using an amide bond was carried out using an amine-functionalized prophyrin (TPP-NH2) and graphene oxide in N,N-dimethylformamide (DMF). FTIR, UV-vis absorption, and TEM studies were also carried out to examine covalent functionalization of the graphene. It was observed that the fluorescence of photo-excited TPP-NH2 was quenched by a possible electron-transfer process. These organic solution-processable functionalized graphene material can be used for light harvesting and solar-energy conversion materials for optoelectronic devices.
Article
Reduced graphene oxide (RGO) and silver nanoparticle (AgNP) hybrids (RGO-AgNP) were prepared by a facile one-pot method using Poly (N-vinyl-2-pyrrolidone) as reductant and stabilizer. Folic acid (FA) molecules were attached to the RGO-AgNP by physisorption for targeting specific cancer cells with folate receptors (FRs) and using as Raman reporter molecules. The internalization of the FA loaded RGO-AgNP (RGO-AgNP-FA) inside the FRs-positive cancer cell was confirmed by confocal laser scanning and transmission electron microscopy. The Raman signals of the FA in live cancer cells were detected by confocal Raman spectroscope at 514 nm excitation, indicating that the RGO-AgNP-FA material has great potential as a Raman probe for cancer diagnosis in vitro.
Article
The near-field interaction between fluorescent emitters and graphene exhibits rich physics associated with local dipole-induced electromagnetic fields that are strongly enhanced due to the unique properties of graphene. Here, we measure emitter lifetimes as a function of emitter-graphene distance d, and find agreement with a universal scaling law, governed by the fine-structure constant. The observed energy transfer- rate is in agreement with a 1/d^4 dependence that is characteristic of 2D lossy media. The emitter decay rate is enhanced 90 times (transfer efficiency of ~99%) with respect to the decay in vacuum at distances d ~ 5 nm. This high energy-transfer rate is mainly due to the two-dimensionality and gapless character of the monoatomic carbon layer. Graphene is thus shown to be an extraordinary energy sink, holding great potential for photodetection, energy harvesting, and nanophotonics.
Article
Graphene oxide (GO) thin films on glass and plastic substrates were found to display interesting broadband nonlinear optical properties. We have investigated their optical limiting activity for femtosecond laser pulses at 800 and 400 nm, which could be tuned by controlling the extent of reduction. The as-prepared GO films were found to exhibit excellent broadband optical limiting behaviors, which were significantly enhanced upon partial reduction by using laser irradiation or chemical reduction methods. The laser-induced reduction of GO resulted in enhancement of effective two-photon absorption coefficient at 400 nm by up to similar to 19 times and enhancement of effective two- and three-photon absorption coefficients at 800 nm by similar to 12 and similar to 14.5 times, respectively. The optical limiting thresholds of partially reduced GO films are much lower than those of various previously reported materials. Highly reduced GO films prepared by using the chemical method displayed strong saturable absorption behavior.
Article
This work reports a simple, clean, and controlled hydrothermal dehydration route to convert graphene oxide (GO) to stable graphene solution. The hydrothermally treated GO was characterized using UV−visible absorption spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, and solid state 13C NMR spectra. Compared to chemical reduction processes using hydrazine, the present “water-only” route has the combined advantages of removing oxygen functional groups from GO and repairing the aromatic structures. By controlling the hydrothermal temperatures, we can modify the physical properties of GO and obtain tunable optical limiting performance.
Article
Atomic clusters of metals are an emerging class of extremely interesting materials occupying the intermediate size regime between atoms and nanoparticles. Here we report the nonlinear optical (NLO) characteristics of ultrasmall, atomically precise clusters of gold, which are smaller than the critical size for electronic energy quantization (∼2 nm). Our studies reveal remarkable features of the distinct evolution of the optical nonlinearity as the clusters progress in size from the nonplasmonic regime to the plasmonic regime. We ascertain that the smallest atomic clusters do not show saturable absorption at the surface plasmon wavelength of larger gold nanocrystals (>2 nm). Consequently, the third-order optical nonlinearity in these ultrasmall gold clusters exhibits a significantly lower threshold for optical power limiting. This limiting efficiency, which is superior to that of plasmonic nanocrystals, is highly beneficial for optical limiting applications.
Article
A report on a hybrid system of ZnO nanoparticles on multiwalled carbon nanotube (MWNT) scaffolds synthesized for ultrafast nonlinear optical switching, is presented. Resonant micro-Raman Spectroscopy and photoluminescence spectroscopy using He-Cd laser under back-scattering geometry is employed to characterize the as-grown ZnO-beaded MWNTs. The large and ultrafast saturable absorption in ZnO-beaded MWNTs suggests that the samples can be used as saturable absorber devices. Combining the three-photon absorption properties of ZnO with the satiable absorption properties of CNTs to yield ZnO/MWNTs hybrid materials would also find important applications in future multifunctional nanodevices.
Article
Deviations from the usual R −6 dependence of the rate of fluorescence resonance energy transfer (FRET) on the distance between the donor and the acceptor have been a common scenario in the recent times. In this paper, we present a critical analysis of the distance dependence of FRET, and try to illustrate the non-R −6 type behaviour of the rate for the case of transfer from a localized electronic excitation on the donor, a dye molecule to three different energy acceptors with delocalized electronic excitations namely, graphene, a two-dimensional semiconducting sheet and the case of such a semiconducting sheet rolled to obtain a nanotube. We use simple analytic models to understand the distance dependence in each case.
Article
This work presents a survey on the recent progress in laser ablation of a solid target in a confining liquid for the synthesis of nanocrystals with focus on the mechanism of nanocrystal growth. The effects of liquid confinement, thermodynamic nucleation, phase transition, and kinetic growth of the nanostructures are discussed in detail. Besides, a variety of applications of the laser ablation is reviewed, including surface patterning, surface cleaning, and surface coating. Experimental results and theoretical analysis indicate that laser ablation of a solid target in a confining liquid provides an effective means to synthesize nanocrystals, especially for the metastable nanocrystals such as diamond and carbon related materials, immiscible alloys, etc. The laser ablation in liquids has demonstrated the following advantages: (i) a chemically “simple and clean” synthesis, (ii) an ambient conditions not extreme temperature and pressure, and (iii) the new phase formation of nanocrystals may involve in both liquid and solid. These advantages allow us to combine selected solid targets and liquid to fabricate compound nanostructures with desired functions.