Laser spectroscopy of ${\mathrm{Pr}}^{3+}$ ions in ${\mathrm{LiKY}}_{1-x}{\mathrm{Pr}}_x{\mathrm{F}}_5$ single crystals

The visible luminescence of ${\mathrm{Pr}}^{3+}$-doped fluoride ${\mathrm{LiKY}}_{1-x}{\mathrm{Pr}}_x{\mathrm{F}}_5$ crystals $(x=0.001,$ 0.01, 0.02, 0.03, 0.05, and 0.1) has been investigated as a function of concentration and temperature by using time-resolved laser spectroscopy. The temperature-dependent concentration quenching of the ${}^3{P}_0$ fluorescence in the 10–77 K temperature range can be described in the framework of a thermally activated cross-relaxation process involving the ${}^1{D}_2$ and ${}^3{H}_6$ states. However, the single exponential character of the decays at all concentrations and temperatures suggests that energy migration is also present in this system. The fluorescence from the ${}^1{D}_2$ level shows a strong concentration quenching for ${\mathrm{Pr}}^{3+}$ concentrations higher than $x=0.001\mathrm{}$ even at 4.2 K. The time evolution of the decays from the ${}^1{D}_2$ state for concentrations higher than $x=0.001\mathrm{}$ is consistent with a dipole-dipole energy transfer mechanism. Anti-Stokes emission from the ${}^3{P}_0$ level following excitation of the ${}^1{D}_2$ state is also studied for different ${\mathrm{Pr}}^{3+}$ concentrations. Analysis of the upconverted fluorescence decays supports that the mechanism responsible for the upconvertion process is energy transfer. However, this process seems to be complex enough to allow for the use of a single model which could explain the behavior observed.