Abstract:
Photoluminescence and excitation spectra of the concentration series of $\mathrm{SrF}_2$:$\mathrm{Mn}^{2+}$ ($C_\mathrm{Mn}=0.01\div1.5$ %) crystals, as well as their lifetimes at 77 Ê, are studied. The primary purpose of the paper is to detect $\mathrm{Mn}^{2+}$ isomorphism in photoluminescence, reveal its character, and compare the obtained results to the available data on other members of the fluorite homologous series. The luminescent properties of $\mathrm{SrF}_2$:$\mathrm{Mn}^{2+}$ crystals are for the first time explained by the presence of exchange-coupled pairs, cubic and trigonal centers of $\mathrm{Mn}^{2+}$ ions. The presence of noncubic symmetry centers is related to the instability of the $\mathrm{Mn}^{6-}_8$ molecule, which is stipulated by the smaller radius of the manganese ion compared to that of $\mathrm{Sr}^{2+}$, and the striction effect induced by the exchange-coupled pairs. It is assumed that the luminescence of trigonal centers from the second excitation level of the manganese ion is stipulated by the Ham effect.
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