Ab initio theoretical study of 4f→5d transitions in Eu2+-doped CaF2

This is the first study, to our knowledge, to report ab initio embedded cluster calculations of Eu2+-doped CaF2. The 4f→5d transition bands were identified based on the complete active space self-consistent field (CASSCF) and second order perturbation theory (CASPT2) calculations for the energies of the Eu2+ 4f7 and 4f65d1 levels with the spin–orbit interactions. By considering the active space which is derived by distributing 13 electrons (7 open-shell α electrons plus 3 α and 3 β electrons) in 15 active molecular orbitals with Eu 4f, 5d, and 5p as main characters, the predicted transition energy and intensity patterns for the 4f→5d(eg) excited states are in good agreement with the experimental absorption spectra.