The 4f5d configuration and VUV absorption of Pr3+ in YPO4

Crystal field interaction of the 5d electron [HCF(5d)] and the Coulomb interaction between the 5d and the 4f electrons [HC(fd)] are the most important interactions in determining the structure of the 4f5d configuration of Pr3+ in solids. Energy levels of the 4f5d configuration in YPO4:Pr were calculated by diagonalizing the simplified Hamiltonian HCF(5d)+HC(fd). Coulomb exchange interaction compresses the extension of the triplet states, while expands that of the singlet states. Thus, for the triplet states, HC(fd) could be considered approximately as a perturbation to HCF(5d).