The structure of the low-temperature 4fN→4f N-1 5d excitation spectra of Eu 3+ and Tb 3+ doped in crystals LiYF4, YPO4 and CaF2 measured by van Pieterson et al. in 2002 was analyzed and assigned based on the simple model proposed by Duan and co-workers in the last few years. Some complemental discussion on effects of J-mixing on the f-d transition intensities for Eu 3+ due to the f-electron crystal-field interaction H cf （f）, which was ignored in the simple model, was presented. Some previously unexplained peaks for Tb 3+ were interpreted to be spin-forbidden transitions to higher 5d crystal-field levels, or assigned to be f→d excitations with the core 4f7 excited from 8S to 6P, 6I and 6D, respectively. It is shown that the main structure of 4f-5d excitation spectra of Eu 3+ and Tb 3+ can be well interpreted with the simple model .
The ab initio self-consistent DV-Xα (discrete variational Xα) method was used in its relativistic and spin-polarized model to investigate the ground-state electronic structures of the crystal YPO4 and YPO4:RE3+ (RE=Ce, Pr and Sm) and f-d transition energies of the lattice. The calculation was performed on the clusters Y5P10O32 and REY4P10O32 embedded in a microcrystal containing about 1500 ions, respectively. The ground-state calculation provided the locations of the 4f and 5d crystal-field one-electron levels of RE3+ relative to the valence and conduction bands of host, the curve of total and the partial density of states, and the corresponding occupation numbers, etc. Especially, the transition-state calculation was performed to obtain the 4f→5d transition energies of RE3+ in comparison to the experimental observations. The lattice relaxation caused by the dopant ion RE3+ was discussed based on the total energy calculation and the transition-state calculation of the f-d transition energies.
