Structural and optical properties of Er, Yb co-doped Y2O3 thin films

Thin Er³⁺, Yb³⁺ co-doped Y₂O₃ films were grown on (1 0 0) YAG substrates by pulsed laser deposition. Ceramic targets having different active ion concentration were used for ablation. The influence of the rare-earth content and oxygen pressure applied during the deposition on the structural, morphological and optical properties of the films were investigated. The films deposited at the lower pressure, 1 Pa, and at 1/10 Er to Yb doping ratio are highly textured along the (1 1 1) direction of the Y₂O₃ cubic phase. In addition to the crystalline structure, these films possess smoother surface compared to those prepared at the higher pressure, 10 Pa. All other films are polycrystalline, consisting of cubic and monoclinic phases of Y₂O₃. The rougher surface of the films produced at the higher-pressure leads to higher scattering losses and different behavior of the reflectivity spectra. Optical anisotropy in the films of less than 0.004 was measured regardless of the monoclinic structure obtained. Waveguide losses of about 1 dB/cm at 633 nm were obtained for the films produced at the lower oxygen pressure.     

Preparation and luminescent properties of cubic Eu:Y2O3 nanocrystals and comparison to bulk Eu:Y2O3

Y₂O₃:Eu³⁺ nanocrystals were prepared by combustion synthesis. The particle size estimated by X-ray powder diffraction (XRD) was about 10 nm. A blue-shift of the charge-transfer (CT) band in excitation spectra was observed in Y₂O₃:Eu³⁺ nanocrystals compared with bulk Y₂O₃:Eu³⁺. The electronic structure of Y₂O₃ is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation (GGA) within the scheme due to Perdew-Burke-Ernzerhof (PBE). The calculated results show that the energy centroid of 5d orbital in nanocrystal has increasing trend compared with that in the bulk material. The bond length and bond covalency are calculated by chemical bond theory. The bond lengths of Y₂O₃:Eu³⁺ nanocrystal are shorter than those of the bulk counterpart and the bond covalency of Y₂O₃:Eu³⁺ nanocrystal also has an increasing trend. By combining centroid shift and crystal-field splitting, the blue-shift of the CT band is interpreted.     

Effect of Nd concentration on structural and optical properties of Nd:Y2O3 transparent ceramic

Y₂O₃ transparent ceramics with different Nd concentration (0.1-7.0at%) were fabricated using ZrO₂ as additive. All the samples exhibit high transparency over a broad spectral region. The elements (Y, O and Nd) are uniformly distributed in the ceramic body, and the average grain size increases with Nd content. Based on the absorption spectrum, the Judd-Ofelt intensity parameters are calculated (Ω₂=4.364×10⁻²⁰ cm², Ω₄=3.609×10⁻²⁰ cm² and Ω₆=2.919×10⁻²⁰ cm²). The absorption coefficients increase linearly with Nd³⁺ doping concentration. The absorption cross-section at 804 nm and stimulated emission cross-section at 1078 nm are calculated to be 1.54×10⁻²⁰ and 7.24×10⁻²⁰ cm², respectively. All the emission bands exhibit the highest emission intensities with 1.0at% Nd³⁺ ion content, while the lifetime decreases dramatically from 321.5 μs (0.1at% Nd) to 17.9 μs (7.0at% Nd). According to the emission spectra and measured lifetime, the optimum doping concentration of Nd³⁺ ion in Y₂O₃ transparent ceramic might be around 1.0at%.     

Silica-coated Y2O3:Eu nanoparticles and their luminescence properties

Crystalline Y₂O₃:Eu is of paramount significance in rare earth materials and research on luminescence spectra. In this work, the nanocrystalline Y₂O₃:Eu was coated with silica by a facile solid state reaction method at room temperature. The transmission electron microscope (TEM) photographs showed that the prepared Y₂O₃:Eu particle is polycrystalline with the size of 20 nm, the size of silica-coated particle is about 25 nm. The XPS spectra indicated that the silica layer is likely to interact with Y₂O₃:Eu by a Si-O-Y chemical bond. The luminescence spectra showed that the intensity of ground samples is lower than that of unground ones, the intensity of silica-coated phosphors is higher than that of the ground samples, while almost the same as that of the unground ones. Therefore, the silica coating decreases the surface defects of nanoparticles of the nanocrystalline Y₂O₃:Eu, thus increasing their luminescent intensity.     

Sol-gel derived Y2O3 as an efficient bluish-white phosphor without metal activator ions

In this paper, Y₂O₃ powder phosphors without metal activators were successfully prepared by the sol-gel method. The obtained sample shows an intense bluish-white emission (ranging from 350 to 600 nm, centered at 416 nm) under a wide range of UV light excitation (235-400 nm). The chromaticity coordinates of the sample are x=0.159, y=0.097, and the quantum yield is as high as 64.6%, which is a high value among the phosphor family without metal activators. The luminescent mechanisms have been ascribed to the carbon impurities in the Y₂O₃ host.     

Optical and electrical properties of Y2O3 thin films prepared by ion beam assisted deposition

Y₂O₃ thin films were deposited by ion beam assisted deposition (IBAD) and the effects of fabrication parameters such as substrate temperature and ion energy on the structure, optical and electrical properties of the films were investigated. The results show that the deposited Y₂O₃ films had less optical absorption, larger refractive index, and better film crystallinity with the increase of substrate temperature or ion energy. The as-deposited Y₂O₃ films without ion-beam bombardment had larger relative dielectric constant (?_r) and the ?_r decreased with time even over by 40%, while the ?_r of films prepared with high ion energy had less changes, only less than 3%. Also, with the increase of ion energy, the electrical breakdown strength and the figure of merit increased.     

Photoluminescent properties of Y2O3:Eu phosphors prepared via urea precipitation in non-aqueous solution

Europium-doped yttrium oxide phosphors were obtained by firing precursors prepared by urea precipitation in ethanol and ethylenediamine. The precipitation in non-aqueous solution was carried out in an autoclave at 150°C to allow the decomposition of urea. The photoluminescent intensities of the phosphors prepared in ethanol and ethylenediamine increased by about 30% compared to that of the phosphor prepared by the conventional urea homogeneous precipitation in aqueous solution. Amorphous carbonates and amorphous hydroxides/carbonates mixtures were identified as precursors from ethanol and ethylenediamine, respectively. The morphology and particle size were studied by SEM and dynamic laser scattering method.     

Tm2O3相对于Si的能带偏移研究

利用分子束外延系统在Si (001) 衬底上制备了单晶Tm₂O₃薄膜, 利用X射线光电子能谱研究了Tm₂O₃相对于Si的能带偏移. 得出Tm₂O₃相对于Si的价带和导带偏移分别为3.1 eV± 0.2 eV和1.9 eV± 0.3 eV, 并得出了Tm₂O₃的禁带宽度为6.1 eV± 0.2 eV. 研究结果表明Tm₂O₃是一种很有前途的高k栅介质候选材料. 关键词： 2O₃')" href="#">Tm₂O₃ X射线光电子能谱 能带偏移     

Synthesis and characterization of wire-like and near-spherical Eu2O3-doped Y2O3 phosphors by solvothermal reaction

Eu₂O₃-doped yttrium oxide (3 mol%) [Y₂O₃:Eu(3 mol%)] with wire-like and near-spherical morphologies were prepared by a solvothermal treatment using water, ethanol, ethylene glycol and glycerol as reaction media followed by calcination. The powders prepared in water and ethanol possessed wire structure, where the powder treated in water showed high aspect ratio and that in ethanol showed low aspect ratio. The powders prepared in ethylene glycol and glycerol possessed well-dispersed near-spherical powders, which showed almost the same level of photoluminescence emission intensity as that of submicron particles prepared without solvothermal treatment.     

Enhanced luminescence of Dy in Y3Al5O12 by Bi co-doping

In the present paper, phosphors with the composition Y_3−x−yAl₅O₁₂:Bi³⁺_x, Dy³⁺_y were synthesized with solid state reactions. The luminescence properties of Bi³⁺ and Dy³⁺ in Y₃Al₅O₁₂(YAG) and the energy transfer from Bi³⁺ to Dy³⁺ were investigated in detail. Bi³⁺ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states ³P_{0, 1} to ground state ¹S₀. Dy³⁺ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state ⁴F_9/2 to ground states ⁶H_15/2 and ⁶H_13/2. The co-doping of Bi³⁺ enhances the luminescent intensity of Dy³⁺ by ∼7 times because Bi³⁺ can transfer the absorbed energy to Dy³⁺ efficiently. The mechanism of energy transfer was also discussed.     

Effects of Tb doping on the photoluminescence of Y2O3:Tb nanophosphors

The effects of Tb doping on the photoluminescence (PL) of Y₂O₃:Tb nanophosphors have been investigated. Nanophosphors were prepared by the glycine-nitrate solution combustion technique using yttria and terbia powders as precursors. PL excitation spectra at room temperature consist of two overlapping bands centered at 277 and 304 nm, whereas emission spectra comprise several groups of lines corresponding to the ⁵D₄→⁷F_J (J=1-6) 4f electronic transitions of the Tb⁺³ ions. A direct comparison of nanophosphor and bulk concentration-quenching curves was obtained by annealing the nanophosphor powder and converting it to bulk material without altering the Tb concentration. The peak in the nanophosphor concentration-quenching curve occurs at a concentration ∼3 times higher than that of the bulk.     

Effect of Eu,Tb codoping on the luminescent properties of Y2O3 nanorods

Red-emitting Y₂O₃:Eu³⁺ and green-emitting Y₂O₃:Tb³⁺ and Y₂O₃:Eu³⁺, Tb³⁺ nanorods were synthesized by hydrothermal method. Their structure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The photoluminescence (PL) property of Y₂O₃:Eu³⁺,Tb³⁺ phosphor was investigated. In the same host (Y₂O₃), upon excitation with ultraviolet (UV) irradiation, it is shown that there are strong emissions at around 610 and 545 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺ and ⁵D₄-⁷F₅ transition of Tb³⁺, respectively. Different qualities of Eu³⁺and Tb³⁺ ions are induced into the Y₂O₃ lattice. From the excitation spectrum, we speculate that there exists energy transfer from Tb³⁺ to Eu³⁺ ions .The emission color of powders reveals regular change in the separation of light emission. These powders can meet with the request of optical display material for different colors or can be potentially used as labels for biological molecules.     

Theoretical investigation of optical spectra and covalent effect of Cr in Y2Ti2O7 and Y2Sn2O7

In this work, the complete matrix of optical spectral levels in trigonal symmetry of 3d² (3d⁸) ions are established on basis of strong field coupling mechanism by using two spin–orbit coupling parameters model. The contribution of the spin–orbit coupling of ligand to the optical spectra has been included in these formulas. As an application, the optical spectra of Cr⁴⁺ in Y₂Ti₂O₇ and Y₂Sn₂O₇ have been studied by the complete diagonalization (energy matrix) method. The covalent effect has been studied and the difficulty about Dq parameter in explanation of optical spectra of Cr-doped Y₂Ti₂O₇ and Y₂Sn₂O₇ is removed. The theoretical results are in good agreement with observed data.     

Upconversion emission enhancement of TiO2 coated lanthanide-doped Y2O3 nanoparticles

To investigate the upconversion emission,this paper synthesizes Tm3+ and Yb3+ codoped Y2O3 nanoparticles,and then coats them with TiO2 shells for different coating times.The spectral results of TiO2 coated nanoparticles indicate that upconversion emission intensities have respectively been enhanced 3.2,5.4,and 2.2 times for coating times of 30,60 and 90 min at an excitation power density of 3.21×102 W.cm 2,in comparison with the emission intensity of non-coated nanoparticles.Therefore it can be concluded that the intense upconversion emission of Y2O3:Tm3+,Yb3+ nanoparticles can be achieved by coating the particle surfaces with a shell of specific thickness.     

Y2O3:Eu纳米晶中能量传递相互作用的研究

通过浓度猝灭曲线确定了引起Y₂O₃纳米晶中Eu³⁺发光浓度猝灭的是交换相互作用.测量了两种颗粒尺寸下Eu³⁺的⁵D₀—⁷F₂跃迁发光衰减曲线随掺杂浓度的变化,利用交换相互作用的理论衰减曲线对实验衰减曲线进行拟合.计算Eu³⁺离子的交换相互作用能量传递的效率,分析了Y₂O_{3关键词： 能量传递 2}O₃Eu纳米晶')" href="#">Y₂O₃Eu纳米晶 发光衰减     

Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method using α-Fe₂O₃ and γ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ₃ and τ₄ are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3 wt% to 40 wt%, the lifetime τ₃ keeps nearly unchanged, while the longest lifetime τ₄ shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ₄ is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Physical and electrical characteristics of a high-k Yb2O3 gate dielectric

High-k ytterbium oxide (Yb₂O₃) gate dielectrics were deposited on Si substrate by reactive sputtering. The structural features of these films after postdeposition annealing treatment were studied by X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the Yb₂O₃ gate dielectrics annealed at 700 °C exhibit a larger capacitance value, a lower frequency dispersion and a smaller hysteresis voltage in C-V curves compared with other annealing temperatures. They also show negligible charge trapping under high constant voltage stress. This phenomenon is mainly attributed to the decrease in the amorphous silica thickness.     

The up-conversion properties of Yb and Er doped Y4Al2O9 phosphors

Er³⁺ doped and Yb³⁺/Er³⁺ co-doped Y₄Al₂O₉ phosphors are prepared by the sol-gel method. The effect of dopant concentration on the structure and up-conversion properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to monoclinic. Under 980 nm excitation, the green and red up-conversion emissions are observed and the emission intensities depended on the Yb³⁺ ion concentration. The green up-conversion emissions decrease with the increase of Yb³⁺ concentration, while red emission increases as Yb³⁺ concentration increases from 0 to 8 at% and then decreases at high Yb³⁺ concentration. The mechanisms of the up-conversion emissions are discussed and results shows that in Er³⁺ and Yb³⁺/Er³⁺ co-doped system, cross-relaxation (CR) and energy transfer (ET) processes play an important role for the green and red up-conversion emissions.     

Y2O3:Yb3+,Tm3+纳米材料的可见及紫外上转换发光

通过燃烧法制备了Yb³⁺-Tm³⁺共掺的Y₂O₃纳米粉体,并对样品在980 nm激光照射下的上转换发光特性进行了研究.实验发现,样品在可见光区域能够产生强烈的蓝色发光(476 nm和487 nm)和较弱的红色发光(约650 nm),而且同时观察到了两个紫外发光峰¹I₆→³H₆ (~297 nm)和^{1关键词： 2O₃:Yb3+')" href="#">Y₂O₃:Yb3+ 3+}')" href="#">Tm³⁺ 上转换光谱 敏化 紫外发光