Analysis of angular overlap parameters for Eu 3+: Ln 2O 2S (LnLu, Y, Gd, La) crystal series

Abstract

The angular overlap model (AOM) is applied to 4f 6 electron systems. The crystal field parameters are interpreted and covalency between 4f electrons and ligands is investigated based on the experimental energy levels. For Eu 3+:Ln 2O 2S (LnLu, Y, Gd, La) crystal series, we adopt two computational schemes. First of all, we assume that the distances to all ligands are equal, and then the distances to all ligands are divided into two groups, namely, oxygens as one group, sulfurs as the other. Of course, much information about covalency will be obtained from the latter case. Obviously, our results show that the covalency of LnO bonding is stronger than that of LnS bonding in line with much shorter bondlength for the former than that for the latter. The two schemes yield the same results, that is, for σ and π bonding, ligands are strong donors as well as σ, π effects are dominant over δ, φ effects.