Theoretical Studies of EPR Parameters for Cr3+ Ion at an Orthorhombic Defect Site in AgBr Crystal

In this paper, the high-order perturbation formulas of EPR zero-field splittings D, E and g-factors g(i) (i = x, y, z) for d(3) ions in orthorhombic symmetry are established by using a two-spin-orbit coupling parameter model, in which both contributions from the spin-orbit coupling of the central d3 ion and that of the ligands are included. Based on these formulas, the EPR parameters for the Cr3+ ion at an orthorhombic defect site in the AgBr crystal are calculated by considering the suitable defect-induced lattice distortion. The calculated parameters D and E show good agreement with the observed values. The reasons for the disparity of the g(i)-shift Delta g(i) = (g(i) - g(s)) between the calculation and the experiment and the importance of the contributions to the EPR parameters from the spin-orbit coupling of ligands are discussed.