Photoluminescence of manganese-doped LiNaGe$_4$O$_9$ crystals

The excitation spectra and photoluminescence spectra of manganese-doped LiNaGe$_4$O$_9$ crystals have been studied experimentally. It has been shown that the manganese ions provide strong red and weak yellow-green luminescences, whose intensities differently change upon the transition of the crystal from the paraelectric to ferroelectric phase. The possible localization and charge state of the manganese ions in LiNaGe$_4$O$_9$ crystals have been discussed.