Spectra and energy levels of ${\mathrm{Tm}}^{3+}$:${\mathrm{Y}}_3$${\mathrm{Al}}_5$${\mathrm{O}}_{12}$

Absorption spectra of ${\mathrm{Tm}}^{3+}$:${\mathrm{Y}}_3$ ${\mathrm{Al}}_5$ ${\mathrm{O}}_{12}$ are reported between 1.9 and 0.26 μm at 15 and 90 K, and between 0.80 and 0.35 μm at 1.6 K. Laser-excited emission obtained at 80 K is also reported from the ${\mathrm{Tm}}^{3+}$ manifolds ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$, ${}_{}{}^1{}_{}{}^{}\mathrm{G}_4^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{H}_4^{}{}_{}{}^{}$, and ${}_{}{}^3{}_{}{}^{}\mathrm{F}_4^{}{}_{}{}^{}$ to the ground-state manifold, ${}_{}{}^3{}_{}{}^{}\mathrm{H}_6^{}{}_{}{}^{}$. The emission from ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$ also includes transitions to Stark levels in manifolds ${}_{}{}^3{}_{}{}^{}\mathrm{F}_4^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{F}_3^{}{}_{}{}^{}$, and ${}_{}{}^3{}_{}{}^{}\mathrm{F}_2^{}{}_{}{}^{}$. Analysis of the emission spectra confirms the experimental crystal-field splitting deduced from an analysis of the hot-band absorption data. Both emission and absorption spectra indicate that ${\mathrm{Tm}}^{3+}$ ions occupy several different sites although the majority of ${\mathrm{Tm}}^{3+}$ ions appear to substitute for ${\mathrm{Y}}^{3+}$ ions in dodecahedral lattice sites ($D_2$ point-group symmetry). The most intense spectra are analyzed assuming selection rules for $D_2$ symmetry. A lattice-sum calculation predicts a symmetry of ${\Gamma }_2$ for the ground state. Using this result the symmetries of 20 ${\Gamma }_1$, 11 ${\Gamma }_2$, 17 ${\Gamma }_3$, and 18