Nonionic surfactant-assisted hydrothermal synthesis of YVO4:Eu3+ powders in a wide pH range and their luminescent properties

YVO₄:Eu³⁺ powders with different morphologies were fabricated by a simple hydrothermal method at 180 °C for 24 h in a wide pH range with the assistance of polyvinylpyrrolidone (PVP) as a nonionic surfactant. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The obtained results showed that the pH value of synthesis solution played a key role in the formation of final products with different morphologies, such as, microspheres, irregular microspheres with grain-like nanoparticles, stone-like structures with regular short nanorods, and smooth rhombohedrons. The PL measurements revealed that the emission intensity of the samples was first decreased, and then increased with increasing the pH value due mainly to the increase in crystallinity and decrease in surface defects.     

Preparation and luminescent properties of YVO4:Eu3+ nanofibers by electrospinning

This paper describes a procedure based on electrospinning for generating europium-doped yttrium vanadate (YVO4:Eu3+) nanofibers with diameters ranging from 30 to 50 nm. The YVO4:Eu3+ nanofibers were obtained through calcining precursory nanofibers, which were prepared through the electrospinning method. Suitable electrospinning parameters, such as concentration of PVP in solution, spinneret tip-to-collector plate distance (TCD), and applied voltage between spinneret and collector plate, are used to obtain thinner and more uniform precursory nanofibers of YVO4:Eu3+, which is important for preparing smaller diameter pure YVO4:Eu3+ nanofibers. The luminescent properties of the YVO4:Eu3+ nanofibers including excitation and emission spectra and fluorescence lifetime were studied. The excitation spectrum shows a broad band extending from 200 to 350 nm, which corresponds to the strong vanadate absorption in YVO4:Eu3+. The emission spectrum is dominated by the red 5D0 --> 7F2 hypersensitive transition of Eu3+. The fluorescence lifetime of Eu3+ 5D0 --> 7F2 (619 nm) is determined to be 493 micros at room temperature, which is basically in accordance with that in the bulk (521 micros).     

Luminescence properties of nanocrystalline YVO4:Eu3+ under UV and VUV excitation

Single phase of Eu³⁺-doped YVO₄ nanophosphors at different pH values were synthesized by a mild hydrothermal method. Their photoluminescence were evaluated under UV and VUV region, respectively. Monitoring by 619 nm emission, broad bands at around 143 nm, 200 nm, 260 nm were observed in the excitation spectrum of YVO₄:5 mol%Eu³⁺. These peaks could be assigned to host absorption, the overlap of the VO₄³⁻ host absorption and charge transfer transition between Eu³⁺ and O²⁻, respectively. Both 254 nm and 147 nm excitations, the emission spectra were identical, they were all composed of Eu³⁺ emission transitions arising mainly from the ⁵D₀ level to the ⁷F_J (J = 1, 2, 3, 4) manifolds. With the pH values ranging from 7 to 11, the relative intensity of the emission spectra were decreasing, and the position of the predominant peak (⁵D₀ → ⁷F₂) was changed from 619 nm to 615 nm when the pH values changed from 7 to 11.     

Preparation and luminescent properties of doped with Eu3+ ions YVO4 nanophosphors

YVO₄:Eu³⁺ nanophosphors were prepared by a sol–gel method. The structure and luminescent properties of YVO₄:Eu³⁺ nanophosphors are characterized by XRD and luminescent spectrophotometer. There are excellent luminescent properties for YVO₄:Eu³⁺ nanophosphors. The nanophosphors are applied in bioapplications field.     

Polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis of luminescent YVO4:Eu3+ microspheres

Spherical YVO₄:Eu³⁺ microstructures were hydrothermally synthesized by the reaction of NH₄VO₃, Y₂O₃, and Eu₂O₃ at 180 °C for 24 h with the assistance of polyvinylpyrrolidone (PVP) as a surfactant. The resulting products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The experimental results showed that ball-like YVO₄:Eu³⁺ microspheres with a diameter of about 4–5 μm, corresponding to the SEM observations, formed at 180 °C for 24 h using 0.2 g PVP with the molecular weight of 20,000 g mol^?1. The amount of PVP and the reaction time of hydrothermal processing were found to play a key role in the formation of YVO₄:Eu³⁺ microspheres. It has been observed that the relative luminescence intensities of the as-synthesized samples increased with increasing hydrothermal reaction times due mainly to the increase of crystallinity.     

燃烧法合成CaMoO4∶Eu3+及其发光性能的研究

采用柠檬酸作为燃料,通过燃烧法制备了CaMoO4蓝色以及CaMoO4:Eu3+红色荧光粉.研究了Eu3+的掺入、反应温度以及反应时间对所制得的CaMoO4:Eu3+的晶体结构以及发光性能的影响.XRD谱图分析显示合成样品CaMoO4和CaMoO4:Eu3+均为白钨矿型晶体结构,晶体的结晶度随着合成温度的升高以及保温时间...     

Hydrothermal synthesis and luminescent properties of GdVO4 : Eu3+ nanophosphors

Eu³⁺-doped GdVO₄ has been synthesised via hydrothermal method by altering the hydrothermal temperature, reaction time and surfactant. The microstructure and morphology information of the phosphors were investigated via the techniques of X-ray powder diffraction and scanning electronic microscopy, which show that the phosphors wear tetragonal phase and the products present various regular morphologies under different reaction conditions such as bulk and nanoparticle. Moreover, the morphologies of the products have been controlled by altering reaction temperature. In addition, the surfactant was also included to control the morphologies of the products and the phosphors present different morphologies. All the phosphors exhibit the characteristic fluorescence of Eu ion (⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₂). The electric dipole transition ⁵D₀ → ⁷F₂ of Eu³⁺ is dominant indicating that most sites of Eu³⁺ ions in GdVO₄ have no inversion centre. Furthermore, we found that the reaction time and the morphologies have great influence on optical properties.     

Na2EDTA-assisted hydrothermal synthesis and luminescent properties of YVO4:Eu3+ with different morphologies in a wide pH range

Nano- and micro-scaled Eu-doped yttrium orthovanadate (YVO₄:Eu³⁺) powders had been fabricated via disodium ethylenediamine tetraacetate (Na₂EDTA)-assisted morphology controllable hydrothermal method in a wide pH range at 180 °C for 24 h. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The results showed that the pH value of the synthesis solution played a key role in the formation of the final products with different morphologies, including ball-like micro-spheres, micro-spheres composed of submicron cubes and flower-like structures containing nano-plates. The photoluminescence measurement revealed that the luminescent properties of the samples were changed by varying their morphologies. The significant ball-like micro-spheres of YVO₄:Eu³⁺ particles had been synthesized, and the luminescence intensity of them is the strongest one among all products.     

Molten salt synthesis and luminescent properties of YVO4:Ln (Ln = Eu3+, Dy3+) nanophosphors

Eu3+ and Dy(3+)-doped YVO4 nanocrystallites were successfully prepared at 400 degrees C in equal moles of NaNO3 and KNO3 molten salts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanocrystallites. XRD results demonstrate that NaOH concentration and annealing temperature play important roles in phase purity and crystallinity of the nanocrystallites, the optimum NaOH concentration and annealing temperature being 6:40 and 400 degrees C respectively. TEM micrographs show the nanocrystallites are well crystallized with a cubic morphology in an average grain size of about 18 nm. Upon excitation of the vanadate group at 314 nm, YVO4:Eu3+ and YVO4:Dy3+ nanocrystallites exhibit the characteristic emission of Eu3+ and Dy3+, which indicates that there is an energy transfer from the vanadate group to the rare earth ions. Moreover, the structure and luminescent properties of the nanocrystallites were compared with their bulk counterparts with same composition in detail.     

Molten salt synthesis and luminescent properties of YVO4:Ln (Ln = Eu3+, Dy3+) nanophosphors

Eu3+ and Dy(3+)-doped YVO4 nanocrystallites were successfully prepared at 400 degrees C in equal moles of NaNO3 and KNO3 molten salts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanocrystallites. XRD results demonstrate that NaOH concentration and annealing temperature play important roles in phase purity and crystallinity of the nanocrystallites, the optimum NaOH concentration and annealing temperature being 6:40 and 400 degrees C respectively. TEM micrographs show the nanocrystallites are well crystallized with a cubic morphology in an average grain size of about 18 nm. Upon excitation of the vanadate group at 314 nm, YVO4:Eu3+ and YVO4:Dy3+ nanocrystallites exhibit the characteristic emission of Eu3+ and Dy3+, which indicates that there is an energy transfer from the vanadate group to the rare earth ions. Moreover, the structure and luminescent properties of the nanocrystallites were compared with their bulk counterparts with same composition in detail.     

低温熔盐合成YVO4:Eu3+红色荧光粉及其发光性能研究

采用低温熔盐法合成了YVO4:Eu3+红色发光材料,用X射线粉末衍射对其结构进行表征,证实样品为具有锆石结构的YVO4相;扫描电镜结果表明,低温熔盐法合成的样品粒径明显小于高温固相法,而且显著降低了烧结温度;荧光光谱分析表明:YVO4:Eu3+的激发光谱在250～350nm范围内有极强宽带吸收,对应于Y3+-O2-、E...     

Nanostructured CaWO4, CaWO4:Eu3+ and CaWO4:Tb3+ particles: sonochemical synthesis and luminescent properties

Nanostructured CaWO4, CaWO4:Eu3+, and CaWO4:Tb3+ phosphor particles were synthesized via a facile sonochemical route. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, low voltage cathodoluminescence spectra, and photoluminescence lifetimes were used to characterize the as-obtained samples. The X-ray diffraction results indicate that the samples are well crystallized with the scheelite structure of CaWO4. The transmission electron microscopy and field emission scanning electron microscopy images illustrate that the powders consist of spherical particles with sizes from 120 to 160 nm, which are the aggregates of even smaller nanoparticles ranging from 10 to 20 nm. Under UV light or electron beam excitation, the CaWO4 powder exhibited a blue emission band with a maximum at 430 nm originating from the WO4/2- groups, while the CaWO4:Eu3+ powder showed red emission dominated by 613 nm ascribed to the 5D0 --> 7F2 of Eu3+, and the CaWO4:Tb3+ powders showed emission at 544 nm, ascribed to the 5D4 --> 7F5 transition of Tb3+. The PL excitation and emission spectra suggest that the energy is transferred from WO4/2- to Eu3+ CaWO4:Eu3+ and to Tb3+ in CaWO4:Tb3+. Moreover, the energy transfer from WO4/2- to Tb3+ in CaWO4:Tb3+ is more efficient than that from WO4/2- to EU3+ in CaWO4:Eu3+. This novel and efficient pathway could open new opportunities for further investigating the novel properties of tungstate materials.     

Shape controlled synthesis,characterization and photoluminescence properties of YVO4:Dy3+/Eu3+ phosphors

Raisin-like, grape-like and box-like nanocrystalline samples of YVO₄:Dy³⁺(2 at.wt%)/Eu³⁺(4 at.wt%) have been synthesized by different preparative routes. The raisin-like nanocrystalline sample has been synthesised by a facile hydrothermal process, whereas a surfactant-assisted synthesis led to the formation of grape-like and box-like nanocrystalline samples, under different reaction conditions. The resulting products were characterised by XRD, TEM, FTIR and photoluminescence spectroscopy. One significant outcome of the photoluminescence study involved a detailed observation of the variations in the relative intensity of the ⁵D₀–⁷F₂ transition with respect to the ⁵D₀–⁷F₁ transition of Eu³⁺ in YVO₄:Eu³⁺, and the relative intensity of ⁴F_9/2–⁶H_13/2 transition with respect to the ⁴F_9/2–⁶H_15/2 transition of Dy³⁺ inYVO₄:Dy³⁺. The observations in either case were subsequently explained on the basis of change in the local symmetry of the dopant ion, due to the change in the host morphology. The presented results strongly indicate that the local environment around the dopant ion changes with the change in the host morphology, which in turn influences the chromaticity of the prepared phosphors (both YVO₄:Eu³⁺ and YVO₄:Dy³⁺).     

掺铕氧化钇发光纳米晶的拉曼光谱研究

采用凝胶燃烧法制备了8～50nm的Y2O3:Eu3+纳米晶.利用XRD确定了纳米晶的结构及晶粒大小,测定了不同晶粒大小的纳米晶Y2O3:Eu3+的拉曼光谱.通过测定不同的激发光所激发的拉曼光谱,以及比对荧光谱,指认了纳米晶Y2O3:Eu3+的Raman振动光谱,并且观察和研究了Raman光谱随晶粒尺寸的变化,发现了低维材料的一些反常拉曼效应.     

Effects of high pressure on the luminescent properties of nanocrystalline and bulk Y2O3:Eu3+

High pressure-induced spectral changes in a 20-nm cubic nanocrystalline yttria doped with europium and its corresponding bulk were studied in the range of 550-750 nm, corresponding to the 5D0 --> 7Fd (J = 0-4) transitions. The results demonstrate that the bulk Y2O3 underwent phase transition from the cubic phase to the monoclinic phase as the pressure increased to 15 GPa, while the 20-nm nanocrystals did not. This can be concluded from the fact that the 5D0 --> 7F0 line and the three 5D0 --> 7F1 sublines originating from the cubic phase disappeared, while another group of 5D0 --> 7F0 and 5D0 --> 7F1 lines appeared. In addition, the relative intensity of the peak around 630 nm to that around 611 nm varied obviously as the pressure surpassed 15 GPa. The variations in the nanocrystals were more sluggish in comparison to those in the bulk, indicating that the nanocrystalline yttria had improved compressibility, which is attributed to an increased surface energy in nanocrystals. The local environment surrounding luminescent Eu3+ in the nanocrystals and the bulk both became more disordered with the increase of the pressure. The phase transition from the cubic to the monoclinic is irreversible.     

Hydrothermal synthesis and characterization of YVO4-based phosphors doped with Eu3+ ion

Nanocrystalline yttrium orthovanadate (YVO₄): Eu powders with different morphologies were synthesized in basic media by surfactant-assisted hydrothermal process. The structures and optical properties of products were investigated using the X-ray powder diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Results showed that pH value played a key role in the formation of products with different morphologies. The photoluminescence measurement showed that the samples with different morphologies exhibited different properties. The dependence between the fluorescence and the microstructure was discussed.     

Magnetic and luminescent properties of Fe3O4@Y2O3:Eu3+ nanocomposites

The multifunctional Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites were prepared by a facile solvothermal method with Fe₃O₄ nanoparticles as the core and europium-doped yttrium oxide (Y₂O₃:Eu³⁺) as the shell. It is shown that Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites have a strong photoluminescence and special saturation magnetization Ms of 6.1 emu/g at room temperature. The effects of the magnetic field on the luminescence intensities of the nanocomposites are being discussed. The multifunctional nanocomposites with magnetic resonance response and fluorescence probe properties may be useful in biomedical applications, such as cell separation and bioimaging.     

Photoluminescent properties of nanostructured Y2O3:Eu3+ powders obtained through aerosol synthesis

Red emitting Y₂O₃:Eu³⁺ (5 and 10 at.%) submicronic particles were synthesized through ultrasonic spray pyrolysis method from the pure nitrate solutions at 900 °C. The employed synthesis conditions (gradual increase of temperature within triple zone reactor and extended residence time) assured formation of spherical, dense, non-agglomerated particles that are nanostructured (crystallite size ∼20 nm). The as-prepared powders were additionally thermally treated at temperatures up to 1200 °C. A bcc Ia-3 cubic phase presence and exceptional powder morphological features were maintained with heating and are followed with particle structural changes (crystallite growth up to 130 nm). Emission spectra were studied after excitation with 393 nm wavelength and together with the decay lifetimes for Eu³⁺ ion ⁵D₀ and ⁵D₁ levels revealed the effect of powder nanocrystalline nature on its luminescent properties. The emission spectra showed typical Eu^{3+ 5}D₀ → ⁷F_i (i = 0, 1, 2, 3, 4) transitions with dominant red emission at 611 nm, while the lifetime measurements revealed the quenching effect with the rise of dopant concentration and its more consistent distribution into host lattice due to the thermal treatment.