Luminescence properties of Y2O3:Bi3+, Ln3+ (Ln=Sm,Eu, Dy,Er, Ho) and the sensitization of Ln3+ by Bi3+

The spectroscopic characterization of yttria, singly and doubly doped with Ln³⁺ (Ln=Sm, Eu, Dy, Er, Ho) and Bi³⁺ ions, is performed through excitation spectra, emission spectra and decay time measurements. The obtained spectroscopic data clearly indicate that energy transfer takes place from Bi³⁺ to Ln³⁺ ions. The energy transfer efficiency of Bi³⁺→Ln³⁺ and quantum efficiency of Ln³⁺ were calculated. Upon excitation of 370 nm (Bi³⁺ excitation band), the quantum efficiency of Ln³⁺ varies from ～4% to ～44%. The energy transfer efficiency increases continuously with increasing Ln³⁺ concentrations, whereas the variation of the quantum efficiency of Ln³⁺ is complicated. The quantum efficiency of Ln³⁺ is discussed in terms of electron transfer and cross relaxation.     

Tm，Ho双掺杂YV04晶体中Tm对Ho敏化发光现象

摘要：报道了对Tm,Ho双掺YVO4晶体光谱性能的测量结果,包括用UV-365型分光光度计测出单掺Tm：YVO4及Ho：YVO4吸收谱以及双掺Tm：Ho：YVO4的吸收谱;用Ar离子激光器488nm,LD激光器激发测量样品荧光光谱;用J-O理论进行光谱参数计算及对能级结构进行分析;研究了在λ=805nm的激光二极管激发下Tm对Ho的敏化发光过程。发现与YAG,YLF为基质的Tm,Ho双掺材料相比,该材料中的Tm3+离子具有大而均匀的吸收宽度(～26nm),大的峰位吸收截面和积分吸收截面(～1.4×10-20cm2和274.5×10-20 cm),能量转换效率高(可达87％),且泵浦阈值低(～15mW)。表明了YVO4晶体中Tm能有效地敏化Ho,并产生2μm的发射。文中对发射强度与泵浦功率及Tm,Ho之间掺杂浓度的关系进行了初步的分析与讨论。光谱的观察结果表明：在实现LD泵浦,全固体化,小型,高效的,2μm激光振荡的探索中,Tm：Ho：YVO4晶体将是一种很有实际应用潜力的材料。     

Hypersensitive transitions of Tm3+, Ho3+ and Dy3+ rare-earth ions in garnet crystals

In this work, spectroscopic characteristics (oscillator strengths, intensity parameters) of intermanifold f–f transitions of Tm^{3 +}, Ho³⁺and Dy³⁺ions in garnet crystals are investigated. It has been found that the intensity change of the hypersensitive intermanifold f–f transitions of rare-earth ions in garnet crystals is determined by the characteristics of their local environment.     

Highly efficient cooperative energy transfer from Ho3+ and Tm3+ ions to Ce3+ ions in crystals

A phenomenon of highly efficient cooperative energy transfer from Ho³⁺ and Tm³⁺ ions to two-particle (2Ce³⁺) cooperative acceptors in crystals of solid solutions of La_1?x Ce _x F₃ is revealed. The rates of cooperative energy transfer in Ho³⁺→2Ce³⁺, Tm³⁺→2Ce³⁺, and Tb³⁺→ 2Yb³⁺ systems are measured, as well as their dependence on the magnitude of the matrix elements of donor transition.     

Photoluminescence properties of red-emitting phosphors Ln3BWO9:Eu3+ (Ln=Y,La, Gd)

Undoped and Eu³⁺ activated Ln₃BWO₉ (Ln=Y, La, Gd) were prepared by the Pechini method and characterized with X-ray diffraction (XRD) and ultraviolet (UV) spectroscopy. All the samples have the hexagonal phase after heat treatment in the range of 850–1000 °C. The Eu³⁺ doped samples emit high-purity red light with peak maximum at about 617 nm under excitation of UV light (～285 nm) at room temperature. When the doping concentration of Eu³⁺ is about 20–30%, luminescence intensity reaches the maximum. Luminescence decay curves indicate that Ln₃BWO₉:Eu³⁺ exhibits a fast decay time of about 0.5 ms. A possible luminescence mechanism has also been proposed. It is worth noting that both the absorption of host lattice and the charge transfer (CT) transition of Eu³⁺ are of great importance to the promising luminescent performance of Ln₃BWO₉:Eu³⁺.     

Thermal Behavior of the Fluorescence Lines of Ho3+ in Cr,Tm,Ho:YAG

The fluorescence spectra of Cr,Tm,Ho∶YAG crystal have been detected at the temperature from 65 to 295 K with interval of 10 K.The width and the shift of Ho3+ lines at 4959.6 cm-1 (at 65 K) have been investigated and interpreted in terms of the interactions between lattice vibration (phonons) and ions.The results showed that the line broadening with the temperature was mainly due to the Raman scattering of phonons,and the line shift with temperature was mainly due to the emission and absorption of virtual phonons.     

Fluorescence Spectra of Eu3+ and Tb3+ Doped Na6 Ln (BO3)3 (Ln = La,Gd, Y) Phosphors

The fluorescence properties of Eu^{3 +} and Tb³⁺ doped Na₆La(BO₃)₃, Na₆Gd(BO₃)₃, Na₆Y(BO₃)₃, Na₆(Gd, Y) (BO₃)₃ powder phosphors are reported. These phosphors display fluorescent RED and GREEN colours when droped with Eu³⁺ and Tb³⁺ ions, respectively. The best fluorescence performance was consistantly observed from the Na-Gd based hosts. The photoluminescence spectra were analysed by evaluating colour coordinates, relative intensity ratios, and stimulated emission cross-sections.     

Cascade-avalanche up-conversion in Tm3+:YLF crystals

New efficient mechanisms of long-wavelength excitation of short-wavelength luminescence in a system of rare-earth impurity ions are proposed. The model studied involves a multilevel system of electronic states of a rare-earth ion interacting with the long-wavelength emission that is in resonance with one or several transitions between the excited levels. The concentration of impurity ions is assumed to be sufficiently high, so that the interionic cross-relaxation and the up-conversion play a significant role. Moreover, the model includes processes similar to photon avalanche, in which the photoinduced excitation of a single ion is converted into lower-level excitations of several ions, each of them reentering the process after photon absorption. Numerical solutions of the system of balance equations for a multilevel system are obtained with calculated and semiempirical parameters of self-quenching and up-conversion. It is shown that, in a system of Tm³⁺ impurity ions, short-wavelength luminescence at λ≥0.29 μm can be efficiently excited by radiation at λ?1.11 or 0.649 μm with a moderate intensity.     

LnZr(BO3)2:Eu3+(Ln=Ba,Sr)的真空紫外光谱特性的研究

采用高温固相法合成了Ba(1-x)SrxZr(BO3)2:Eu3 系列样品,样品Ba(1-x)SrxZr(BO3)2:Eu3 激发谱在130～170nm和230 nm区域有两个很强的吸收带,位于130～170nm的吸收带主要是硼酸盐基质的吸收;位于230nm附近的吸收主要是Eu3 电荷转移态的吸收.当在样品中以Al部分取代Zr时,电荷转移态的吸收明显增强,并且Ba(1-x)SrxZr(BO3)2:Eu3 发射强度也会明显增强;随着x的增大,硼酸盐基质的吸收强度减弱,基质吸收带的主峰值向低能方向移动了大约30 nm.样品Ba(1-x)SrxZr(BO3)2:Eu3 在147nm激发下,发射出主峰值位于616nm的强红光,对应Eu3 电偶极(5D0→7F2)跃迁发射.     

Magnetismus in den intermetallischen SEAu3-Verbindungen (SE=Gd,Tb, Dy,Ho, Er und Tm)

The relation between inner displacement and strain is established and simplified by group theory. Results are given for the diamond structure (C, Ge, Si), cobalt (Co), graphite (C), neodymium (Nd), spinel (MgAl₂O₄). For these crystals we get an enormous reduction of the number of parameters to be determined by measurement.     

氟化物玻璃中Tm^3＋离子敏化Ho^3＋离子的红外发光性质

研究了氟化物玻璃中Ｔｍ＾３＋和Ｈｏ＾３＋离子的红外吸收光谱性质，用钛宝石激光器作为激发源，研究了Ｔｍ＾３＋离子的交叉弛豫过程和Ｔｍ＾３＋敏化Ｈｏ＾３＋２μｍ的红外发射光谱。研究结果表明，只有发Ｔｍ＾３＋离子浓度较高（～２ｗｔ％）时，才能发生较强的交叉弛豫进行，随Ｍｏ＾３＋离子浓度的增加，２μｍ的发光强度增大，当激发光波长为８１３ｎｍ时，２μｍ的发光强度最大。     

Spectroscopy of YVO4:Ho3+ crystals

Crystals of YVO₄:Ho were grown by the Czochralski method. The structure of the low-energy levels of Ho³⁺ has been estimated experimentally. Intensity parameters, radiative lifetimes, and branching ratios have been calculated in the framework of the Judd–Ofelt theory. The influence of temperature on luminescence lifetimes has been investigated. The calculated nonradiative transition rate was compared with the energy-gap law. The potential laser gain for the ⁵ I ₇–⁵ I ₈ transition has been estimated. Received: 27 June 2001 / Final version: 10 December 2001 / Published online: 7 February 2002     

Synthesis and luminescent properties of spindle-like YVO4:Ln3+ (Ln=Eu,Dy) self-assembled of nanoparticles

Large-scale spindle-like YVO₄ particles with an euatorial diameter of 100–150 nm and a length of 300–350 nm were synthesized by utilizing the Y(OH)CO₃ colloid spheres as the precursor and NH₄VO₃ as the vanadium source through a simple solution-based hydrothermal process, for the first time. In the first stage of the reaction, hierarchical flower-like YVO₄ spheres were formed. Then, petals of spindle-like YVO₄ particles were obtained via a following self-abscission process from these flower spheres. The possible formation mechanism has been discussed in detail. Moreover, the photoluminescent properties of spindle-like YVO₄:Ln³⁺ (Ln=Eu, Dy) nanoparticles were investigated. They might have potential application in advanced flat panel display, minioptoelectronic devices, and biological labeling.     

Magnetic resonant and non-resonant investigations of LiLnF4 (Ln = Y, Tm) powders

The properties of dielectric powders of the Van Vleck paramagnet LiTmF₄ and its diamagnetic analogue LiYF₄ have been investigated by both resonant methods (EPR, NMR, and the mass-spectroscopy) and non-resonant ones (conductometry and magnetization measurement). On the basis of experimental data and theoretical calculations a self-consistent model for the magnetic and other properties of these powders is suggested. Two structural phase transitions induced by the magnetic field are discovered in fine LiTmF₄ powder at low temperature in a high magnetic field.