Sharp-Line Luminescence fromOs4+andMo3+inCs2HfCl6

Sharp-line luminescence spectra have been obtained for ${\mathrm{Os}}^{4+}$ ($5{d}^{4}$) and ${\mathrm{Mo}}^{3+}$ ($4{d}^{3}$) in single cubic crystals of ${\mathrm{Cs}}_{2}$Hf${\mathrm{Cl}}_{6}$. For ${\mathrm{Os}}^{4+}$, luminescence from both the $^{1}E({\ensuremath{\Gamma}}_{3})$ and $^{1}T({\ensuremath{\Gamma}}_{5})$ levels of the ${t}^{4}$ configuration to all the spin-orbit split levels of the $^{3}T_{1}$ ground state are observed. Luminescence spectra from the $^{2}E$ ("$R$" lines) of ${\mathrm{Mo}}^{3+}$ are reported for the first time. Sharp vibronic lines are observed in the vicinity of 1. 1 \ensuremath{\mu} due to coupling with odd-mode vibrations of the nearest-neighbor complex. Excitation spectra reveal pumping due to absorption into the $^{4}T_{2}$ and $^{4}T_{1}$ bands at 23.0 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and 19.5 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, and to the $^{2}T$ level at 14.0 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The excitation bands do not correlate with the major absorption bands observed in these crystals, suggesting that other charge states of molybdenum are simultaneously present in the crystals.