Microstructure of pair centers of Cr3+-Cr2+ ions in the KZnF3 crystal

Studies involving the piezospectroscopy method have shown that the symmetry of the pair centers of Cr3+-Cr2+ ions in the KZnF3 crystal is tetragonal. In this paper we develop a microscopic model of a pair center. We use the temperature dependence of the integrated intensity of the absorption line to find the effective hopping integral for an eg electron, tσσ=205 ± 10 cm−1, and the polaron reduction factor, equal to 0.11. By analyzing the selection rules for exchange-induced electric dipole transitions under double-exchange conditions we identify all the absorption lines of Cr3+-Cr2+ pairs.