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.
The Yb3＋ doped Ba2YB＇O6 （B＇= Ta5＋, Nb5＋） were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of yb3＋：Ba2YB＇O6 （B＇= Ta5＋, Nb5＋） were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO6 or NbO6 centre with large Stokes shift. The Yb3＋ doped into these hosts are situated at y3＋ sites of cubic symmetry （Oh）. The experimental energy levels of Yb3＋ in Ba2YTaO6 and Ba2YNbO6 were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg-Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of yb3＋：Ba2YB＇O6 （B＇=Ta5＋, Nb5＋） from （2F5/2）Г8-to the low-energy states were calculated.
