LuTaO4是最高密度的闪烁体基质,研究它的结构及其相变对单晶制备具有指导意义.用固相法制备了Lu2O3和Ta2O5摩尔比为1:1时在不同温度下形成的多晶粉末,用X射线衍射及Rietveld全谱拟合研究了多晶粉末的物相和结构.结果表明,Lu2O3:Ta2O5摩尔比为1:1的样品在1740℃时合成的物相为M′-LuTaO4,在1800℃时为M′-Lu Ta O?4和M-LuTaO4的混合物,在1840C时全部转变为M-LuTaO4.当温度升高到2058℃时,样品呈熔融状态,对淬火得到的样品进行结构精修,给出了M-LuTaO4,Lu3Ta O7和Ta2O5的晶胞和原子坐标参数,它们的重量比分别占78.1%,18.9%和3.0%.这些结果为制备以LuTaO4为基质的高密度闪烁体单晶具有参考价值.
The lutetium tantalate compounds obtained from Lu2O3–Ta2O5 with a molar ratio of 0.515 ： 0.485 were studied by Raman scattering and x-ray diffraction. The results of the room temperature Raman scattering indicate that the sample has a phase transition between 1830℃ and 1872℃, the polycrystalline is a mixture of M-LuTaO4 and Lu3TaO7（F m3m）when it is prepared at 1830℃, and a mixture of M-LuTaO4（B112/b） and Lu3 Ta O7（Fm3^-m） when it is prepared at above 1872℃. The sample melts at a temperature of 2050℃. The phase transition of the sample prepared at 2050℃ was also investigated by the high-temperature Raman spectra, and the result indicates that no phase transition occurs between room temperature and 1400℃, which is consistent with the results from the x-ray diffraction.
采用提拉法生长出了钕掺杂钽酸钆重闪烁单斜激光晶体(Nd3+:Gd Ta O4).分别测试了该晶体a向、b向和c向的吸收光谱(波段为260—2000 nm),对其中Nd3+的实验能级进行了分析指认.确定了Nd3+:Gd Ta O4的102个实验Stark能级,拟合了其自由离子参数和晶体场参数,均方根误差(拟合精度)σ为12.66 cm-1.并将拟合得到的Nd3+:Gd Ta O4实验结果与文献中已报道的Nd3+:GdxLu1-xTa O4(x=0.85)的自由离子参数和晶体场参数进行了比较.结果表明,参数化Stark能级的拟合结果与实验光谱符合得较好.
The crystal structural parameters of Nd ^3＋-doped rare earth orthotantalate Gd x Lu 1 x TaO 4（x = 0.85） are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation spectra at 77 K are analysed.The relativistic model of ab initio self-consistent DV-Xα method,which is applied to the cluster NdO 8 in Gd x Lu 1 x TaO 4,and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters.The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm 1.According to the crystal-field calculations,96 levels of Nd ^3＋ are assigned.Finally,the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd ^3＋：YAlO 3.The results indicate that the free-ion parameters are similar to those of the Nd3＋ in Gdx Lu1-x TaO4 and YAlO 3 hosts,and the crystal-field interaction of Nd^3＋ in Gdx Lu1-x TaO4 is stronger than that in YAlO 3.
An iterative method is used to find the values of the Hamiltonian parameters for Yb^3＋ in a given low-symmetry crys- talline site. Samples of Yb^3＋ ：RETaO4 （RE = Gd, Y, and Sc） were prepared and their structures were determined. Based on the obtained structural data, their orbital-spin parameters and crystal field parameters were fitted by the superposition model （SM）. Using the crystal field parameters obtained by the SM fitting as the initial parameters, the Hamiltonian parameters were fitted iteratively. The calculated and experimental energy levels for Yb^3＋：RETaO4 are consistent, and the maximal mean-root-square deviation is only 2.84 cm^- 1, indicating that the method is effective to determine the Hamiltonian parameters of Yb^3＋ in low-symmetry crystalline sites.
