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Enhanced photoluminescence of core-shell CoFe2O4/SiO2/Y2O3:Eu3+ composite by remanent magnetization

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Abstract

A core-shell cobalt ferrite/silicon dioxide/europium ion-doped Y2O3 (CoFe2O4/SiO2/Y2O3:Eu3+) composite was synthesized by a facile layer-by-layer method. Magnetization of the composite under an external magnetic field of approximately 0.25 T enhanced the photoluminescence (PL) intensity by 56%. The remanent magnetization of the CoFe2O4 core increased the excited charge-transfer transition between O2- and Eu3+ in the Y2O3:Eu3+ shell, thus enhancing the probability of radiative transition (5D0→7F2) of Eu3+ ions and leading to enhanced PL. Remanent magnetization is a noncontact, easy-to-operate technique with high growth amplitude and potential for practical application for smart display devices.

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Aminated-CoFe2O4/SiO2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe2O4/SiO2 NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe2O4/SiO2 NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe2O4/SiO2 NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe2O4/SiO2 NPs can be used as an effective carrier for the enzyme immobilization.Highlights► Monodisperse CoFe2O4/SiO2 NPs with high amino groups’ density were obtained. ► Monodisperse CoFe2O4/SiO2 nanoparticles have superparamagnetism, indicating that the CoFe2O4/SiO2 can be used as carrier for the enzyme immobilization. ► Aminated-CoFe2O4/SiO2 magnetic nanoparticles were prepared by a facile method.
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Monodispersed SiO2/Y2O3:Eu3+ core–shell submicrospheres were prepared through a simply homogeneous precipitation method. SEM, TEM, and Zetasizer analysis indicated the regular microstructures and uniform size distributions of obtained submicrospheres. FTIR spectra showed that the Y2O3:Eu3+ shell had linked to the silica surface by forming a Si–O–Y bond. XRD patterns characterized the crystal structures of deposited Y2O3:Eu3+ shell after heat treatment. Photoluminescence studies showed that the thickness of Y2O3:Eu3+ shell had greatly affected the luminescent property of coated particles.
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A Y2O3–SiO2 nanocomposite doped with Eu3+ was obtained by the sol–gel technique and characterized by powder X-ray diffraction, transmission electron microscopy, NMR and laser-excited luminescence spectroscopy. It was found that small (2–3 nm) Y2O3 nanoparticles, whose size does not appear to change for heat treatments in the range 500–900 °C, interact at the interface with the SiO2 matrix. Luminescence spectroscopy seems to indicate that the Eu3+ ion is preferentially located inside the highly disordered Y2O3 nanoparticles. These luminescent nanocomposites form a class of materials which could find applications in the field of phosphors.
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An improved sol-gel method was employed to prepare Eu3+ ions doped SiO2-Y2O3 nanocomposites. Systematic study was carried out on the effect of post-annealing treatment on photoluminescence (PL) properties of the samples under various europium ions doping concentrations. X-ray diffraction (XRD) patterns indicated that the samples showed an amorphous matrix structure, and the scanning electron microscopy (SEM) pictures showed that the samples presented a nano size (from 21 to 42 nm) granular-stack structure after high-temperature annealing treatment (from 600 to 900 °C, respectively) for 3 h. Raman spectra demonstrated that Y3+ and Eu3+ ions were incorporated into the composites through the sol-gel and post-annealing process. Under the excitation of 394 nm (7F0→5L6) light, red emission was observed around 613 nm (5D0→7F2). Without annealing treatment, the optimized doping amount of Eu ions was about 6.5 mol.%, which was much higher than that single doped in SiO2 glass matrix with Eu ions concentration of 3%, and it raised to 9.0% when the samples were annealed at high-temperature (900 °C) annealing.
Article
This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y2O3:Eu3+) and submicron-sized (Y2SiO5:Ce3+,Tb3+) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO2 using a sol–gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20–90%, depending on the core composition and shell thickness. For Y2O3:Eu3+, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu3+ activator concentration and the luminescence emission intensity of the core/shell particles was 20–50% higher than that of the core particles alone. For Y2SiO5:Ce3+,Tb3+, the core/shell particles showed enhancement of the luminescence emission intensity of 35–90% that of the core particles, depending on the SiO2 shell thickness.
Article
Eu3+-doped Y2O3@SiO2 systems were synthesized using yttrium oxide and TEOS in order to produce glass ceramic nanoparticles. The glass ceramic phosphor system was prepared taking into account two methodologies: the first one (PS) using the crystallized ceramic added into the SiO2 sol, and the second one (SS) crystallizing the Y2O3:Eu3+ directly into the glass matrix. The Y2O3:Eu3+ pure system was also prepared as a reference. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses suggest the formation of Si–O–Y bonds in cubic Y2O3:Eu3+ inside a SiO2 matrix annealed after 700 °C heat treatment. PS and SS powders were composed of nanocrystals with an average size of ∼10 and ∼9 nm, respectively. No structural changes in the signal emitted were observed with the addition of silica shell.
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The energy transfer rate between the two ions in the K dimer of SrF2:Er3+ is measured as a function of magnetic field. A large enhancement is observed in the energy transfer rate because of the field. The previously identified resonant two-phonon-assisted energy transfer mechanism does not predict the large enhancement that was observed because of averaging among all of the processes arising from the magnetically split levels.
Article
It has been experimentally discovered that a low magnetic field (less than 500 mT) can substantially change the electroluminescence, photoluminescence, photocurrent, and electrical-injection current in nonmagnetic organic semiconducting materials, leading to magnetic-field effects (MFEs). Recently, there has been significant driving force in understanding the fundamental mechanisms of magnetic responses from nonmagnetic organic materials because of two potential impacts. First, MFEs can be powerful experimental tools in revealing and elucidating useful and non-useful excited processes occurring in organic electronic, optical, and optoelectronic devices. Second, MFEs can lead to the development of new multifunctional organic devices with integrated electronic, optical, and magnetic properties for energy conversion, optical communication, and sensing technologies. This progress report discusses magnetically sensitive excited states and charge-transport processes involved in MFEs. The discussions focus on both fundamental theories and tuning mechanisms of MFEs in nonmagnetic organic semiconducting materials.
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We report on the unique luminescent properties of nanocrystals of Mn-doped ZnS with varying sizes from 30 to 70A˚prepared at room temperature. These nanosize quantized particles yield the best external photoluminescent quantum efficiency of about 18% at room temperature and luminescent decay time at least five orders of magnitude faster than the corresponding Mn2+ radiative transition in the bulk crystals. These luminescent measurements also suggest that the efficiency increases with decreasing size of the nanocrystalline particles. These novel properties may be attributed to electron-hole localization and hybridization of the s-p host states with d-electrons of the Mn impurity.
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The properties and applications of nanocrystals doped with transition and rare-earth impurities are reviewed. The high efficiency and ultrafast recombination times observed in these doped nanocrystals make these materials very attractive for optoelectronic applications.
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Eu(III)-doped Y(2)O(3) nanocrystals are prepared by microwave synthetic methods as spherical 6.4 ± 1.5 nm nanocrystals with a cubic crystal structure. The surface of the nanocrystal is passivated by acetylacetonate (acac) and HDA on the Y exposed facet of the nanocrystal. The presence of acac on the nanocrystal surface gives rise to a strong S(0) → S(1) (π → π*, acac) and acac → Ln(3+) ligand to metal charge transfer (LMCT) transitions at 270 and 370 nm, respectively, in the Eu:Y(2)O(3) nanocrystal. Excitation into the S(0) → S(1) (π → π*) or acac → Ln(3+) LMCT transition leads to the production of white light emission arising from efficient intramolecular energy transfer to the Y(2)O(3) oxygen vacancies and the Eu(III) Judd-Ofelt f-f transitions. The acac passivant is thermally stable below 400 °C, and its presence is evidenced by UV-vis absorption, FT-IR, and NMR measurements. The presence of the low-lying acac levels allows UV LED pumping of the solid phosphor, leading to high quantum efficiency (∼19%) when pumped at 370 nm, high-quality white light color rendering (CIE coordinates 0.33 and 0.35), a high scotopic-to-photopic ratio (S/P = 2.21), and thermal stability. In a LED lighting package luminosities of 100 lm W(-1) were obtained, which are competitive with current commercial lighting technology. The use of the passivant to funnel energy to the lanthanide emitter via a molecular antenna effect represents a new paradigm for designing phosphors for LED-pumped white light.
Article
Upconversion control: Applying a relatively low bias voltage to an epitaxial lanthanide-doped BaTiO3 thin film results in a significant enhancement of the upconversion emission. Moreover, the photoluminescence (PL) intensity can be modulated with an ac electric field (see picture). This approach provides a real-time and dynamic way to control photoluminescence.
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Uniform magnetite particles stabilized by citrate groups were successfully synthesized by a modified hightemperature solvothermal reaction. Cell imaging reveals that the water-dispersible particles can readily penetrate into cells without destroying them, indicating an excellent biocompatibility. A high enrichment capacity of the magnetite particles for separation of trace peptides is observed.
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In this paper, hydrothermal synthesized Fe3O4 microspheres have been encapsulated with nonporous silica and a further layer of ordered mesoporous silica through a simple sol-gel process. The surface of the outer silica shell was further functionalized by the deposition of YVO4:Eu3+ phosphors, realizing a sandwich structured material with mesoporous, magnetic and luminescent properties. The multifunctional system was used as drug carrier to investigate the storage and release properties using ibuprofen (IBU) as model drug by the surface modification. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, photoluminescence (PL) spectra, and superconducting quantum interference device (SQUID) were used to characterized the samples. The results reveal that the material shows typical ordered mesoporous characteristics, and have monodisperse spherical morphology with smooth surface and narrow size distribution. Additionally, the multifunctional system shows the characteristic emission of Eu3+ (5D0-7F(1-4)) even after the loading of drug molecules. Magnetism measurement reveals the superparamagnetic feature of the samples. Drug release test indicates that the multifunctional system shows drug sustained properties. Moreover, the emission intensities of Eu3+ in the drug carrier system increase with the released amount of drug, thus making the drug release be easily tracked and monitored by the change of the luminescence intensity.
Article
A bright persistent photoluminescence has been observed in Er(3+)-doped nanoparticles prepared by selective dissolution of bulk oxyfluoride nano-glass-ceramics. A 2 orders of magnitude decrease of intensity of the (4)S(3/2)-->(4)I(15/2) green emission band of Er(3+) in these nanoparticles is observed in magnetic fields up to 50 T. This strong luminescence sensitivity to magnetic field can be used for localization and distant optical detection of magnetic field in nanovolumes with a field-resolution of 0.01 T.
Article
Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE2O3 ( RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2-5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 degrees C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D0-->7Fn transition within the cubic form of RE2O3 exhibits some important differences from that usually found in bulk materials.
Comparative study of synthesis and characterization of monodispersed SiO 2 @Y 2 O 3
  • Fu
  • Sun
Fu Y X and Sun Y H 2009 Comparative study of synthesis and characterization of monodispersed SiO 2 @Y 2 O 3 :Eu 3+ and SiO 2 @Y 2 O 3 :Eu 3+ @SiO 2 core–shell structure phosphor particles J. Alloys Compounds 471 190–6