Isotope effects in the multiphonon relaxation of hydrated and deuterated cesium chloromanganate (CsMnCl3·2H2O,·2D2O)

The electronic transition between the $^{4}T_{1}$ and $^{6}A_{1}$ states of the ${\mathrm{Mn}}^{2+}$ ion in CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O has been observed to be weak compared to the same transition in other hosts, due to vibrational quenching. We have observed fluorescence and infrared-absorption spectra of the deuterated compound CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{D}}_{2}$O and report little change in the phonon sideband associated with the pure electronic transition, but observe a 15-fold increase in the lifetime of the excited state, along with an increase in the $^{4}T_{1}$ luminescence intensity. Infrared spectra reveal an intense band of high-frequency phonons which exhibits a large shift in energy with isotopic substitution. We show that these data are consistent with the theory of multiphonon transitions recently presented by Huang and Gu.