Investigations of the g factors and hyperfine structure constants for tetragonal and cubic Co 2+ centers in AgCl crystals

Abstract

In this paper, the calculation formulas based on a cluster approach for the EPR g factors g ‖, g ⊥ , and hyperfine structure constants A ‖, A ⊥ of 3d 7 ions in tetragonal octahedral crystal fields are established. In these formulas, the parameters related to configuration interaction and covalency effects can be obtained from the optical spectra and structural parameters of the studied system. Only one adjustable parameter, the core polarization constant κ, is used for the calculation of A ‖ and A ⊥. From these formulas, the EPR parameters g ‖, g ⊥, A ‖ and A ⊥ for tetragonal Co 2+-V Ag center in AgCl crystal are satisfactorily explained by considering the suitable tetragonal distortion Δ R (i.e., the displacement of the intervening Cl − ion towards Co 2+ ion along the C 4-axis). The local geometry of the Co 2+-V Ag center is therefore obtained. The EPR parameters g and A for cubic Co 2+ center in AgCl are also calculated from the above formulas for the case where the distortion Δ R=0. The results are consistent with the observed values.