STUDIES OF THE LOCAL STRUCTURES FOR THE 2 TETRAGONAL CENTERS IN AGCL-CR-3+ CRYSTALS FROM EPR PARAMETERS

The local structural parameters for the tetragonal Cr3+-V-M and V-M-Cr 3+-V-M centers in AgCl:Cr3+ crystals have been estimated by calculatin g their EPR zero-held splitting and g factors from two theoretical mod els. 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 distor tion Delta R based on the two-SO-parameter model is about 2.2 that bas ed on the one-SO-parameter model for both centers and the reasonablene ss of the former is discussed. It appears that for the d(n) clusters w ith ligands having a large SO coupling coefficient zeta(p), the contri bution of SO coupling of ligands to the EPR parameters cannot be negle cted and so the two-SO-parameter model should be used to explain the E PR parameters, or, conversely, to study the local structures of these clusters from EPR data. (C) 1998 Published by Elsevier Science B.V. Al l rights reserved.