Ab initio theoretical study of 4f→5d transitions in Eu2+-doped CaF2: (2) Augmented-basis-set-study

We report the 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 the second order perturbation theory (CASPT2) calculations for the energies of the Eu2+ 4f7 and 4f65d1 states including the spin-orbit interactions. The active space was 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. To improve the theoretical prediction of the absorption spectra, we added both the diffuse functions on F atoms and the basis functions on the second neighbor Ca atoms to the basis set used in our previous paper [J. Lumin. 145 (2014) 941]. As a result, the predicted 4f→5d (t2g) transition energy and intensity patterns improved slightly; they were also in better agreement with the experimental absorption spectra.