Investigations of the g factors and hyperfine structure constants for tetragonal and cubic Co2+ centers in AgCl crystals

In this paper, the calculation formulas based on a cluster approach for the EPR g factors g(parallel to), g(perpendicular to), and hyperfine structure constants A(parallel to), A(perpendicular to) of 3d(7) ions in tetragonal octahedral crystal fields are established. In these formulas, the parameter s related to configuration interaction and covalency effects can be obtaine d from the optical spectra and structural parameters of the studied system. Only one adjustable parameter, the core polarization constant kappa, is us ed for the calculation of A(parallel to) and A(perpendicular to). From thes e formulas, the EPR parameters g(parallel to), g(perpendicular to), A(paral lel to), and A(perpendicular to) for tetragonal Co2+-V-Ag center in AgCl cr ystal are satisfactorily explained by considering the suitable tetragonal d istortion Delta R (i.e., the displacement of the intervening Cl- ion toward s Co2+. ion along the C-4-axis). The local geometry of the Co2+-V-Ag center is therefore obtained. The EPR parameters g and A for cubic Co2+ center in AgCl are also calculated from the above formulas for the case where the di stortion Delta R = 0. The results are consistent with the observed values. (C) 2000 Elsevier Science B.V. All rights reserved.