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We investigate co-doped ZnSe:(Cr, Fe) laser crystals with an approach that includes both optical spectroscopy and theoretical modeling. We found that concentrations of chromium and iron up to 1018 cm-3 are optimal for obtaining a homogeneous solid solution in designing laser crystals. Higher dopant concentrations lead to the formation of clusters with spinel structure in the ZnSe matrix. The optimal effectiveness of ZnSe laser media with active Cr2+ and Fe2+ elements is achieved at temperatures of around 100 K. Heating induces charge transfers like Fe2+→Fe3+ and Cr2+→Cr3+, while cooling results in temperature quenching. A theoretical model has been developed to explain the observed temperature evolution of the absorption spectrum. The types and values of distortions of the Cr- and Fe-based coordination complexes are determined. We have found that the Jahn-Teller distortions are crucial for modelling the temperature-dependent changes of the absorption spectra.
Lamonova et al. (Wed,) studied this question.