Absorption spectrum of the mixed valence Cr3+-Cr2+ pair center in KZnF3 crystal

Assignment of absorption lines of mixed valence Cr3+- Cr2+ pair center has been done by the analysis of the probabilities of exchange-induced electric-dipole transitions. Parameters of exchange interaction J1 equals 44.5 +/- 5 cm-1 and axial crystal field B02 equals -19.6 +/- 2 cm-1 for the excited state have been estimated from the fine structure of absorption spectra of the pair. Using microscopic theory of superexchange interaction for the ground and excited states of the pair the value of the transfer integral of eg-electron via the intermediate fluorine ion tvv equals 3500 cm-1 has been extracted.