Radiative and nonradiative transitions ofPr3+in trichloride and tribromide hosts

We have measured the fluorescent decay rates of the ${}_{}{}^3{}_{}{}^{}P$ states of the ${\mathrm{Pr}}^{3+}$ ion in trihalide crystals as a function of temperature. When extrapolated to 0 K we find that the fluorescent lifetimes of ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ are 14.7 ± 1.0 μsec (${\mathrm{Pr}}_{0.01}$ ${\mathrm{La}}_{0.99}$ ${\mathrm{Cl}}_3$), 11.5 ± 1.5 μsec (Pr${\mathrm{Cl}}_3$), 12.0 ± 1.0 μsec (${\mathrm{Pr}}_{0.01}$ ${\mathrm{La}}_{0.99}$ ${\mathrm{Br}}_3$), and 1.0 ± 0.12 μsec (Pr${\mathrm{Br}}_3$). By combining the fluorescent decay rates with measurements of the quantum efficiency we have been able to extract the rate for nonradiative transfer of excitation between ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ in the dilute crystals and have found the results in reasonable agreement with a multiple-optical-phonon transition model. In ${\mathrm{Pr}}_{0.01}$ ${\mathrm{La}}_{0.99}$ ${\mathrm{Br}}_3$ we have observed both fluorescence and laser action from the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ state, although this state has not previously been observed in emission in any host. Finally, we present a summary of the laser transitions which we have observed in these hosts.