Structural analysis and crystal-field calculations of Nd³⁺ in Gd_xLu_1-xTaO₄ (x=0.85) polycrytalline

The crystal structural parameters of Nd³⁺-doped rare earth orthotantalate Gd_xLu_1-xTaO₄ (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 NdO₈ in Gd_xLu_1-xTaO₄, 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 Nd³⁺ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd³⁺:YAlO₃. The results indicate that the free-ion parameters are similar to those of the Nd³⁺ in Gd_xLu_1-xTaO₄ and YAlO₃ hosts, and the crystal-field interaction of Nd³⁺ in Gd_xLu_1-xTaO₄ is stronger than that in YAlO₃.