Studies of the local structures for the two tetragonal centers in AgCl : Cr 3+ crystals from EPR parameters

Abstract

The local structural parameters for the tetragonal Cr 3+-V M and V M-Cr 3+-V M centers in AgCl : Cr 3+ crystals have been estimated by calculating their EPR zero-field splitting and g factors from two theoretical models. One is the two spin–orbit (SO) parameter model in which not only the contribution due to the SO coupling of central d 3 ion, but also that of the ligands are included, and another is the conventional one-SO-parameter model where only the contribution due to the SO coupling of the central d 3 ion is considered. The estimated tetragonal distortion Δ R based on the two-SO-parameter model is about 2.2 that based on the one-SO-parameter model for both centers and the reasonableness of the former is discussed. It appears that for the d n clusters with ligands having a large SO coupling coefficient ζ p, the contribution of SO coupling of ligands to the EPR parameters cannot be neglected and so the two-SO-parameter model should be used to explain the EPR parameters, or, conversely, to study the local structures of these clusters from EPR data.