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+ 4f(7) and 4f(6)5d(1) states including the spin-orbit interactions. The active space was derived by distributing 13 electrons (7 open-shell alpha electrons plus 3 alpha and 3 beta 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 (t(2g)) transition energy and intensity patterns improved slightly; they were also in better agreement with the experimental absorption spectra. (C) 2015 Elsevier B.V. All rights reserved.