稀土离子(Eu~(3+),Tb~(3+),Ce~(3+))掺杂ZnAl_2O_4/SiO_2微晶玻璃的制备与发光性能（英文）

采用凝胶法分别制备出4.5ZnO-5.5Al2O3-90SiO2(ZAS)以及ZAS∶RE3+(RE=Eu,Tb,Ce)透明微晶玻璃。利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和荧光光谱仪(PL)等测试手段,研究了稀土离子掺杂浓度对ZAS微晶玻璃的结构和发光性能的影响。XRD结果表明,ZAS∶RE3+(RE=Eu,Tb,Ce)微晶玻璃包含ZnAl2O4晶相和SiO2非晶相,ZnAl2O4平均晶粒尺寸约为30 nm,稀土离子的掺杂没有显著改变原来的ZnAl2O4晶体结构。TEM结果表明,900℃时ZnAl2O4从ZAS体系中析出。PL光谱显示,Eu3+存在5D0→7F2跃迁,ZAS∶Eu3+在611 nm处发出强烈的红色光;由于Tb3+的5D4→7F5跃迁,ZAS∶Tb3+在541 nm处发出明亮的绿色光;ZAS∶Ce3+在381 nm处显示了蓝光发射,对应于Ce3+的5d→4f轨道跃迁。ZAS∶RE3+(RE=Eu,Tb,Ce)的PL发射光谱存在着浓度猝灭现象,Eu3+、Tb3+和Ce3+的最佳单掺杂摩尔分数分别为20%、20%和3%。CIE色度图表明,ZAS∶RE3+(RE=Eu,Tb,Ce)的色坐标分别位于红光、绿光和蓝光区域。实验结果表明,ZAS∶RE3+(RE=Eu,Tb,Ce)微晶玻璃是一种良好的可用于全色显示的白光LED材料。     

稀土离子(Eu3+,Tb3+,Ce3+)掺杂ZnAl2O4/SiO2微晶玻璃的制备与发光性能

采用凝胶法分别制备出4.5ZnO-5.5Al2 O3-90SiO2 (ZAS)以及ZAS∶ RE3+(RE=Eu,Tb,Ce)透明微晶玻璃.利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和荧光光谱仪(PL)等测试手段,研究了稀土离子掺杂浓度对ZAS微晶玻璃的结构和发光性能的影响.XRD结果表明,ZAS∶ RE3+(RE=Eu,Tb,Ce)微晶玻璃包含ZnAl2 O4晶相和SiO2非晶相,ZnAl2 O4平均晶粒尺寸约为30 nm,稀土离子的掺杂没有显著改变原来的ZnAl2O4晶体结构.TEM结果表明,900℃时ZnAl2O4从ZAS体系中析出.PL光谱显示,Eu3+存在5 D0→7F2跃迁,ZAS∶Eu3+在611 nm处发出强烈的红色光;由于Tb3+的5D4→7E跃迁,ZAS∶ Tb3+在541 nm处发出明亮的绿色光;ZAS∶ Ce3+在381 nm处显示了蓝光发射,对应于Ce3的5d→4f轨道跃迁.ZAS∶RE3+(RE =Eu,Tb,Ce)的PL发射光谱存在着浓度猝灭现象,Eu3+、Tb3+和Ce3+的最佳单掺杂摩尔分数分别为20％、20％和3％.CIE色度图表明,ZAS∶ RE3+(RE=Eu,Tb,Ce)的色坐标分别位于红光、绿光和蓝光区域.实验结果表明,ZAS∶RE3+(RE=Eu,Tb,Ce)微晶玻璃是一种良好的可用于全色显示的白光LED材料.     

Ho3+掺杂GeO2-Ga2O3-Li2O-BaO-La2O3玻璃的光谱和增益特性的计算

用高温熔融法制备了不同Ho3+浓度掺杂的65GeO2-12Ga2O3-8Li2O-10BaO-5La2O3-χHo2O3锗酸盐玻璃.从吸收光谱出发,应用Judd-Ofelt理论,获得了Ho3+离子的跃迁强度参量（Ω2,Ω4,Ω6）,并由此计算了Ho3+离子的自发辐射跃迁几率A,荧光分支比β,辐射能级寿命τ等光谱参量.根据McCumber理论,计算了Ho3+离子能级5I8→5I7（2.0 μm）跃迁的吸收截面和受激发射截面,同时也获得了相应的反映粒子数反转的增益截面光谱.钬掺杂的锗酸盐玻璃,其增益截面的最大值比所报道的氟锆铝酸盐玻璃大.结果表明,Ho3+掺杂的锗酸盐玻璃在2.0 μm附近波段的中红外激光器中将有一定的应用前景.     

Gd_2O_3∶(Ce~(3+),Eu~(3+))微晶中稀土离子间的级联能量传递

本文报道了纳米Gd2 O3∶(Ce3+ ,Eu3 + )的紫外与真空紫外 (UV VUV)激发谱及其选择激发下的荧光光谱。这些光谱实验表明 ,除了Gd2 O3 基质与Ce3+ ,Eu3 + 离子之间的能量传递外 ,还存在着Gd3+ 与Ce3 + 、Eu3 +间的能量传递 ,即存在Gd3+ →Ce3+ →Eu3 + 三种稀土离子间的级联传递     

电子俘获型材料Sr_3SiO_5∶Eu~(2+),RE~(3+)(RE=Nd~(3+),Ho~(3+),La~(3+))的光激励和长余辉发光性能的研究

通过高温固相法制备出系列电子俘获型材料Sr3SiO5∶Eu2+,RE3+(RE=Nd3+,Ho3+,La3+),并对其光激励和长余辉性能进行了研究。经过紫外光源激发后,利用980nm激光照射时,表现出很强的上转换光激励信息读出响应,其归因于较深陷阱(438K)的存在,这种性能在Sr3SiO5∶Eu2+,La3+和Sr3SiO5∶Eu2+,Ho3+两种材料表现尤为明显。随后,对陷阱的深度和载流子浓度进行了研究,并分析产生光激励性能的原因。热释光光谱中电子俘获参数的计算是通过Chen’s半宽方法,得出438K所对应的陷阱深度值,并与980nm激光辐照光源的能量形成对比。与此同时,共掺稀土离子后的余辉性能也有着较大幅度的提高,Sr3SiO5∶Eu2+,La3+的余辉时间更是达到12h以上。研究结果显示,共掺样品的陷阱结构的改变是导致其光激励及余辉性能的根本原因。     

Ho3+:LiYF4晶体的中红外发光特性

用坩埚下降法制备了Ho3+离子掺杂的LiYF4单晶。测定了Ho3+:LiYF4晶体的偏振吸收光谱。应用Judd-Ofelt理论分别计算了Ho3+:LiYF4晶体中Ho3+离子的有效强度参数Ω2,4,6、能级跃迁振子强度fexp和fcal、自发辐射跃迁几率A、荧光分支比β、辐射寿命τrad等光谱参数。测定了样品在640 nm光激发下的红外发射光谱,观测到由Ho3+离子的5I6→5I7跃迁所致的2.8～3μm中红外发光,以及在1.2μm(5I6→5I8)和2.0μm(5I7→5I8)处较强的荧光。Ho3+:LiYF4单晶样品的吸收峰线宽较宽,计算得到1.2μm和2.0μm的峰值发射截面分别达到0.20×10-20cm2和0.51×10-20cm2,同时测定了1 191 nm(5I6→5I8)和2 059 nm(5I7→5I8)发射的荧光寿命。研究结果表明:Ho3+:LiYF4晶体在2.0～3μm波段的中红外激光器中有较大的应用前景。     

Tm3+和Ho3+双掺氟锗酸盐玻璃的中红外发光性质质

用高温熔融法制备了Tm3+和Ho3+离子双掺的65GeO2-12AlF3-10BaF2-8Li2O-5La2O3氟锗酸盐玻璃,应用Judd-Ofelt理论,获得了Ho3+离子的强度参量（Ω2,Ω4,Ω6）,自发辐射跃迁几率Ar,辐射寿命τ等光谱参量。根据McCumber理论,计算了玻璃中Tm3+和Ho3+离子的吸收截面σa、受激发射截面σe和增益光谱G(λ)。在808nm激光二极管激发下,研究分析了Tm3+离子的交叉弛豫过程和Tm3+敏化Ho3+离子的2.0µm的红外发射光谱。结果表明,一定浓度Ho3+的共掺提高了Tm3+（3F4）→Ho3+（5I7）之间的能量转移效率,增强了~2.0µm的红外发光。     

Yb3+敏化的Er3+/Ho3+共掺碲酸盐玻璃的上转换发光研究

用高温熔融法制备了系列Er3+/Yb3+共掺,Ho3+/Yb3+共掺,和Er3+/Yb3+/Ho3+三掺碲酸盐玻璃,在975 nm激光抽运下三种掺杂玻璃中都出现了较强的绿光和红光上转换.研究了Yb3+离子对Er3+和Ho3+离子上转换发光强度的影响以及Yb3+→Er3+,Yb3+→Ho3+能量传递效率.分析了碲酸盐玻璃中Yb3+直接敏化Er3+,Ho3+上转换发光机理.当Er3+和Ho3+浓度较低时,Er3+/Yb3+/Ho3+三掺玻璃的上转换强度随着Yb3+离子浓度的增加而增强,出现的548 nm绿光和660 nm红光主要是由于Er3+:4S3/2→4I15/2,Ho3+:5F4(5S2)→5I8和Er3+:4F9/2→4I15/2,Ho3+:5F5→5I8跃迁共同作用的结果.Er3+/Yb3+/Ho3+三掺碲酸盐玻璃的上转换机理受Er3+/Yb3+之间,Ho3+/Yb3+之间,Er3+/Ho3+之间三者共同相互作用影响,Er3+/Ho3+离子间存在的交叉弛豫过程可增加Ho3+离子在可见光范围的上转换强度.     

Eu~(2+),Cr~(3+)共掺杂SrAl_(12)O_(19)发光体的发光性质及能量传递

采用高温固相法制备了Eu2+,Cr3+单掺杂及共掺杂的SrAl12O19发光体,研究了它的发光性质和能量传递动力学过程。Eu2+的5d→4f发射峰位于400 nm,与Cr3+位于350~450 nm波长范围的4A2→4T1的吸收带有显著的光谱重叠,有利于Eu2+→Cr3+的能量传递发生,从而将来自于Eu2+离子的紫光转换为Cr3+的深红光发射。在共掺杂的样品中,当激发Eu2+时观察到Cr3+离子的2E→4A2红色线谱发射。当监测该红色线谱发射时,激发光谱中包含有Eu2+的吸收,证明了在SrAl12O19体系中Eu2+→Cr3+能量传递的存在。能量传递导致Eu2+的荧光寿命随Cr3+浓度的增加而缩短,计算表明能量传递效率随Cr3+浓度增加而提高,当Cr3+浓度为5%时能量传递效率可达到50%。     

LaOX:Ho3+体系的荧光光谱及其配位场解析

合成了LaOX:Ho3+磷光体(X-=Cl-,Br-),测定了该体系在室温和液氮温度下的荧光光谱;基于双层点电荷配位场模型,计算了Ho3+离子在LaOX系列基质中的配位场微扰能级,给出其荧光光谱的理论归属;这套能级与实测光谱吻合较好,并对5I8→5G6超灵敏跃迁激发带的“鞍形”结构、5I8→5G6及(5S2,5F4)→5I8跃迁峰的温度效应提出合理解释。     

Structural refractometry of β- and β″-Al2O3-type aluminates and gallates

The ionicity of oxide and β- and β″-Al₂O₃ crystals is identified via Lorentz–Lorenz molar refractivity. The investigation was extended to sodium gallates, the refractivity and average refractive index of which are estimated.     

Electronic band structure of KTaO3

Calculations are presented for the electronic band structure of the perovskite-type crystal KTaO₃. The results are obtained using the LCAO method in a modified form. On comparison with experimental data good agreement was found after a reassignment of one transition.     

Sol–gel template synthesis and characterization of LaCoO3 nanowires

Densely packed LaCoO₃ nanowires of the rare-earth perovskite-type composite oxide were synthesized within a porous anodic aluminum oxide (AAO) template by means of the sol–gel method using nitrate as raw the material and citric acid as the chelating agent. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the LaCoO₃ nanowires possessed a uniform length and diameter, which were controlled by the thickness and the pore diameter of the applied AAO template, respectively. The results of X-ray diffraction (XRD) and the selected area electron diffraction (SAED) indicated that the LaCoO₃ nanowires had a rhombohedral perovskite-type crystal structure. Furthermore, X-ray photoelectron spectroscopy (XPS) demonstrated that LaCoO₃ nanowires were formed. Finally, the formation mechanism of nanowires was also discussed. PACS 61.66.Fn; 61.46.-W; 81.20.Fw     

A semi-empirical equation for oxygen nonstoichiometry of perovskite-type ceramics

Explicit equations correlating oxygen nonstoichiometry to oxygen partial pressure and temperature are important for applications of perovskite-type ceramics as membranes, adsorbents and catalysts in various chemical reaction and separation processes. A semi-empirical equation for oxygen nonstoichiometry on perovskite-type ceramics is reported in this paper. Though derived from the results of a point defect model on a perovskite-type ceramic material, La_0.1Sr_0.9Co_0.5Fe_0.5O_3−δ, this equation describes very well the experimentally measured oxygen nonstoichiometry data for two perovskite-type ceramics measured in this work and three perovskite-type ceramics reported in the literature. The major advantage of this semi-empirical equation lies in its simplicity, explicitness and accuracy. This equation is coupled with oxygen permeation equation to predict oxygen permeation current density through two perovskite-type ceramic membranes. The predicted data agree very well with the results reported in the literature using a complex defect reaction model.     

Li and Nb codoping in dielectric properties and phase transitions of KTaO3: Reentrant dipolar glass and long-range dipole ordering

Abstract

The highly polarizable perovskite-type oxide, KTaO₃ doped simultaneously with Li⁺ and Nb⁵⁺ (K_1?xLi_xTa_1?yNb_yO₃, KLTN), reveals unexpected properties and ordering effects. Studies of the dielectric permittivity ?'(T, f) (10—300K, 100Hz-1 MHz) for x = 0.0014 and y = 0.024 show collective dipolar ordering effects with a transition from paraelectric into a mixed phase (coexisting dipole-glass-like and long-range ordered ferroelectric phases) taking place near 39 K. At 15 K another phase transition into a reentrant dipolar glass-like state is observed. Such a sequence of transitions and the existence of a reentrant glass state are unknown for electrical dipolar systems.     

Edge and surface antiferromagnetism in ABO3 perovskite-type nanoparticle within the effective field theory

ABSTRACT

The edge and surface antiferromagnetic properties of the ABO₃ perovskite-type nanoparticle and their components (A, B and O) are investigated through the Effective Field Theory developed by Kaneyoshi. It is found that the Edge AntiFerroMagnetism (EAFM) causes a decrease in the Curie temperature and separation in the magnetizations. However, the Surface AntiFerroMagnetism (SAFM) causes a compensation behaviour (T_Comp?=?1.23) in the total magnetisation of the ABO₃ perovskite-type nanoparticle. The magnetisation of the central B component has been affected by the edge antiferromagnetism more strongly than by the surface antiferromagnetism. Moreover, coercivity (Hc) and remanence magnetizations (Mr) decrease for the EAFM, but they increase for the SAFM. Triple hysteresis behaviour is obtained for the SAFM. Therefore, it is suggested that there is a strong relationship between the compensation behaviour and the triple hysteresis behaviour.     

The relationship between crystal structure and electrical conductivity in the LaY1−xInxO3 (x=0.0–0.7) system

The electrical conductivity of the LaY_1−xIn_xO₃ (x=0.0–0.7) system has been studied from the viewpoint of crystal chemistry. The high temperature form of LaYO₃ (x=0.0) was ascertained to be the Sm₂O₃-type (B-type rare earth) structure, not perovskite-type one. The X-ray diffraction (XRD) experiments revealed that the samples with x=0.05 and 0.10 were the mixed phase of Sm₂O₃-type and perovskite-type structure, and changed to perovskite phase in the range of x0.20. From oxygen partial pressure dependence of the electrical conductivity, it was found that both the Sm₂O₃-type and the perovskite-type single phases showed hole conduction, but the mixed phase did oxide-ion one. The electrical conductivity of the LaY_1−xIn_xO₃ (x=0.0–0.7) system increased with increasing x, and showed the maximum value in the range of x=0.05–0.10, and then decreased with increasing x. The occurrence of oxide-ion conduction was discussed from the viewpoint of lattice distortion in the mixed phase.     

Optical losses in YVO4: RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO₄: Nd and YVO₄: Er is not significant except for that from the ⁴ I _11/2 level of Er³⁺. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO₄: Er laser slope efficiency when the Er³⁺ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the ³ F ₄-³ H ₆ laser operation near 1800 nm in the YVO₄: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.     

Phase transitions in AgTaO3 single crystals

AgTaO₃ single crystals have been obtained by the molten salt method; two different solvents, AgCl and V₂O₅, were used. X-ray investigations have been carried out in the temperature region from 300 K to 800 K. At room temperature AgTaO₃ possesses a pseudocubic perovskite-type unit cell with rhombohedral distortion. Two structural phase transitions, to tetragonal at 650 K and to cubic symmetry at 770 K, have been observed. In the tetragonal phase a jump of the lattice constants has been observed at approximately 680 K. DTA and domain structure investigations confirm the presence of these phase transitions.     

First-Principles Calculations for Thermodynamic Properties of Perovskite-Type Superconductor MgCNi3

The ground state properties and equation of state of the non-oxide perovstdte-type superconductor MgCNi3 are investigated by first-principles calculations based on the plane-wave basis set with the local density approximation （LDA） as well as the generalized gradient approximation （GGA） for exchange and correlation, which agree well with both theoretical calculations and experiments. Some thermodynamic properties including the heat capacity, the thermal expansion coefficient and the Griineisen parameter for perovskite structure MgCNi3 are obtained. The dependences of these thermodynamic properties on pressure and temperature are given for the first time.