Electroluminescence of Y2O3:Eu and Y2O3:Sm films

Electroluminescence of Y₂O₃:Eu and Y₂O₃:Sm films, as well as the films coactivated with Eu and Sm, is studied. The electroluminescence spectra are measured. The physical mechanism of electroluminescence is analyzed It is shown that the increase in the heat treatment temperature and the content of doping impurities of the films enhances the intensity of electroluminescence. Additional doping of Y₂O₃:EuF₃ films by the SmF₃ impurity, practically does not influence the emission spectrum.     

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.     

Synthesis and characterization of rod-like Y2O3 and Y2O3:Eu3+

Y₂O₃ rods 100 to 200 nm in diameter and 10 to 20 m in length are accessible via polyol-mediated synthesis of a precursor material with similar shape. By heating of Y(CH₃COO)₃ · xH₂O and a defined amount of water at 190°C in diethylene glycol, the rod-like precursor material is formed. Infrared spectroscopy (IR), differential thermal analysis (DTA) and thermal gravimetry (TG) evidence that this precursor material still contains acetate. However, the precursor material can be transformed to Y₂O₃ by sintering at 600°C without destruction of the rod-like shape. According to X-ray powder diffraction analysis, the rods are well crystallized. They can be assumed to be with [100] orientation. By doping with Eu³⁺ (5 mol%), red emitting phosphor rods can be realized. With optical spectroscopy the typical line emission of Eu³⁺ is observed. Diffuse reflectance of Y₂O₃:Eu³⁺ rods is determined to be higher than 95% in the visible. While exciting at 254 nm (Hg-discharge), a quantum efficiency of 38.5% is proven for the prepared Y₂O₃:Eu³⁺ rods.     

纳米Y_2O_3:Eu~(3+)(Y_2O_3)粉体的红外光谱研究

采用均相沉淀法和燃烧合成法制备了不同粒径的粉体材料Y2O3:Eu3+,着重研究了样品的红外光谱,探讨了纳米晶Y2O3:Eu3+与同质微米材料相比的微观结构的变化.研究发现,波数位于563 cm-1的Y(Eu)—O键的吸收峰校正高度和面积对于纳米级粒径的粉体材料随着颗粒的减小而减小,而对于同质微米材料却相反.经分析认为:Y(Eu)—O键的吸收峰校正高度和面积由Y(Eu)—O键的平均键长和Y(Eu)—O键振动态数目这两个因素决定.对于微米粉体Y(Eu)—O键长的变化起主要作用,而对于纳米粉体由于不饱和键和悬空键的形成,Y(Eu)—O键振动态数目的变化起主要作用.     

Structural transition in nanostructured Eu2O3 under high pressures

We report here studies on the effect of high pressure on the structural properties of nano-sized Europium sesquioxide (Eu2O3) up to a pressure of about 16.4 GPa. At ambient conditions, the starting sample was found to be predominantly cubic type Eu2O3 or in Eu3+ state with a trace of Eu2+. The presence of Eu2+ state is assumed to be arising due to the non-stoichiometric Eu(1-x)O phase which is obtained from XPS studies by the deconvolution of the Eu 3d-core levels. The Raman studies at ambient show a strong peak at about 333 cm(-1), which is known to occur due to the Fg mode of cubic Eu2O3 and in a similar way, the XRD data shows major peaks corresponding to the cubic phase of Eu2O3. A Mao-Bell type diamond anvil cell (DAC) was used to generate high pressures for XRD and Raman spectroscopy studies. It was observed that the material undergoes a structural change from cubic to monoclinic structure with an on set transition pressure at around 2 GPa and completes at around 8 GPa. This has been inferred from the fact that above about 2.0 GPa pressure, Raman studies show the emergence of a new peak corresponding to the monoclinic phase which increases in intensity and shifts further with increase in pressure, while the XRD studies show that above about 2.0 GPa, the peaks corresponding to monoclinic phase emerge, which show a slight increase in preferred orientation as the pressure is increased. A detailed discussion has been provided to explain this fact.     

Morphology-tailored synthesis of flower-like Y2O3:Eu3+ microspheres

Flower-like Y₂O₃:Eu³⁺ microspheres with strong red photoluminescent emission were successfully synthesized through a controlled solvothermal approach followed by a subsequent heat treatment. The experimental results showed that the flower-like microspheres were composed of nanopetals with the thickness of about 50 nm, and the solvent properties as well as the characteristics of the reactants were very crucial for the morphology-controlled process. Meanwhile, the formation mechanism study revealed a possible assembly and etching process. In addition, their photoluminescence property investigation indicated that the flower-like products exhibited the strongest red emission corresponding to ⁵D₀ → ⁷F₂ transition (609 nm) among the synthesized samples, implying better photoluminescence property provided by the assembled spheres with higher crystallinity and better size-distribution and suggesting their potential application in optoelectronics.     

Homogeneous coatings of nanosized Fe2O3 particles on Y2O2S:Eu

The red emitting phosphor Y₂O₂S:Eu commonly applied in colour television tubes was pigmented with a thin homogeneous layer of nanosized Fe₂O₃ particles based on a novel coating strategy. In a first step the phosphor was covered with nanosized Fe₃O₄ particles which themselves were prepared by reduction of an Fe(III)-salt with hydrazine. Thereafter, Fe₃O₄ was converted to Fe₂O₃ by heating to 450°C in air. Surface composition and body colour of the corresponding phosphor samples were investigated applying ESCA and measuring diffuse reflectance. The size of the Fe₂O₃ particles as well as the homogeneity of the resulting coating were studied by SEM. Furthermore, the adhesion of Fe₂O₃ particles on the phosphor surface was examined.     

Fabrication of photoluminescent S doped Y2O3:Eu3+ nanobelts

We have successfully fabricated the S doped Y(OH)3 nanobelts with 15-30 microm in length and 50-300 nm in width and S doped Y(OH)3:Eu3+ nanobelts with 4-15 microm in length and 80-500 nm in width (most between 100 and 200 nm) via a similar process for preparation of Y(OH)3 nanotubes. Photoluminescent (PL) nanobelts of S doped Y2O3:Eu3+ were obtained through dehydration of the S doped Y(OH)3:Eu3+ nanobelts at 450 degrees C in N2. The PL properties of the S doped Y2O3:Eu3+ nanobelts have been studied and evidenced that we have successfully synthesized functional S doped Y2O3:Eu3+ nanobelts with interesting photoluminescence properties.     

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.     

Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles

Cubic and/or monoclinic Y₂O₃:Eu³⁺ nanoparticles (10–50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700–1300°C for 10 h) as-prepared, initially monoclinic Y₂O₃:Eu³⁺ nanoparticles resulting in larger 0.025–1 μm, cubic Y₂O₃:Eu³⁺. The influence of europium (Eu³⁺) content (1–10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y₂O₃:Eu³⁺ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y₂O₃ particles at 900, 1100 and 1300°C for 10 h, the PL intensity increased as particle size increased and finally (at 1300°C) showed similar PL intensity as that of commercially available, bulk Y₂O₃:Eu³⁺ (5 μm particle size). Eu doping stabilized the monoclinic Y₂O₃ and shifted the monoclinic to cubic transition towards higher temperatures.     

Detection of H2S gas at lower operating temperature using sprayed nanostructured In2O3 thin films

Nanostructured indium oxide (In₂O₃) thin films were prepared by spray pyrolysis (SP) technique. X-ray diffraction (XRD) was used to investigate the structural properties and field emission scanning electron microscopy (FESEM) was used to confirm surface morphology of In₂O₃ films. Measurement of electrical conductivity and gas sensing performance were conducted using static gas sensing system. Gas sensing performance was studied at different operating temperature in the range of 25–150 °C for the gas concentration of 500 ppm. The maximum sensitivity (S = 79%) to H ₂ S was found at lower temperature of 50 °C. The quick response (4 s) and fast recovery (8 s) are the main features of this film.     

Y2O3:Eu3+ core-in-multi-hollow microspheres: facile synthesis and luminescence properties

Y2O3:Eu3+ core-in-multi-hollow microspheres were synthesized via a facile hydrothermal method in the presence of glucose followed by a subsequent heat-treatment process. X-ray diffraction (XRD) pattern shows that the as-obtained hollow spheres are cubic phase of Y2O3. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images indicate that the samples are three layer hollow spheres with a diameter of 2-4 microm and the outermost wall thickness of 100 nm, the size of the inner core is about 300-400 nm, and the sub-outer wall thickness is about 100 nm. X-ray energy dispersive spectrum (EDS) shows that the samples are composed of Y, Eu and O. Photoluminescence spectra show that the hollow spheres have a strong characteristic red emission corresponding to the 5D0 - 7F2 transition of Eu3+ ions under ultraviolet excitation. This method can be used to synthesize other rare earth oxide hollow luminescent materials.     

EU:Y2O3纳米晶的光谱特性与微结构

采用均相共沉淀法制备了不同粒径的Y2O3：Eu^3＋和Y2O3粉体材料,根据红外光谱和荧光光谱,探讨了纳米Y2O3：Eu^3＋粉体的微观结构与同质体微米材料相对变化.发现纳米粉体的Y（Eu）-O键吸收峰校正高度和面积随着颗粒的减小而减小,而对于同质微米材料却相反.分析认为：Y（Eu）-O键红外吸收峰校正高度和面积由Y（Eu）-O键的平均键长和Y（Eu）-O键振动态的数目两个因素决定,对于微米粉Y（Eu）-O键长起主要作用.由于纳米粉体的比表面积随粒径的减少呈指数的增加,不饱和键和悬空键的数目随粒径减小而指数增加,Y（Eu）-O键振动态的数目起主要作用.计算了纳米粉体相对微米粉的跃迁强度参量Ωt/Ωt＇值,发现Ω2和Ω4均增加,说明粉粒内部跃迁几率增加.纳米荧光粉比微米粉荧光强度减少的实验事实应是纳米粉粒表面效应引起的,与红外光谱实验的结果相符.     

Superconductivity behaviour of screen-printed LnBa2Cu3O7 (Ln=Eu,Y) films

Thick films of the highT _csuperconducting oxides, LnBa₂Cu₃O₇, Ln = Eu, Y, have been fabricated by screen printing on alumina and SrTiO₃ substrates. Conditions for optimum superconductivity behaviour of the films have been established.T _c ^onset varies from 90–94 K for all the films but zero resistance was observed only in a few cases.     

Composite phosphor films based on spherical Lu2O3:Eu3+ nanoparticles

A nanopowder of Lu₂O₃:Eu³⁺ (C _Eu = 5 at.%) was obtained by coprecipitation with urea (NH₂)₂CO from aqueous solutions. Using this nanopowder, compact Lu₂O₃:Eu³⁺ films with thicknesses within 20–200 μm and a relative density up to 65% of the theoretical limit were deposited using the spin-coating and painting techniques. The films were characterized by scanning electron microscopy, X-ray diffraction, and X-ray luminescence (XRL) measurements. It is established that the XRL intensity depends on the phosphor/organic binder ratio and thickness of the film. The most intense XRL and most homogeneous structure are observed for 20-μm-thick Lu₂O₃:Eu³⁺ films.