Spectroscopy and four-wave mixing in Lisub${4\mathrm{G}\mathrm{e}}_5$${\mathrm{O}}_{12}$:${\mathrm{Mn}}^{4+}$ crystals

The absorption and fluorescence spectra of ${\mathrm{Mn}}^{4+}$ in ${\mathrm{Li}}_4$ ${\mathrm{Ge}}_5$ ${\mathrm{O}}_{12}$ crystals are reported and the temperature dependences of the fluorescence intensity and lifetime are described. The spectral features are consistent with the presence of two types of sites for the ${\mathrm{Mn}}^{4+}$ ions, and radiationless decay and vibronic transitions are shown to be responsible for the variation of the spectral properties with temperature. Four-wave mixing measurements were performed with the laser excitation wavelength in resonance with an absorption transition of the ${\mathrm{Mn}}^{4+}$ ions. The characteristics of the four-wave mixing signal are consistent with scattering from a laser-induced population grating and the temperature dependence of the signal is correlated with the temperature dependence of the fluorescence lifetime.