Cooperative energy transfer amongPr3+ions in LaF3

Abstract

We report the discovery of population in the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state (46 986 ${\mathrm{cm}}^{-1\mathrm{}}$) of ${\mathrm{Pr}}^{3+}$ following the excitation of the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state (20 925 ${\mathrm{cm}}^{-1\mathrm{}}$) by a 477.8-nm pulse laser. The energy upconversion is attributed to a cooperative energy transfer from a pair of ${\mathrm{Pr}}^{3+}$ ions in the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state to a nearby ion in the same state. A Pr${\mathrm{F}}_3$ crystal and three La${\mathrm{F}}_3$:${\mathrm{Pr}}^{3+}$ crystals doped with 10, 20, and 60 at.% ${\mathrm{Pr}}^{3+}$ are tested in our experiment. The lifetime of the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state and the decay of the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state of each of the crystals are investigated. The results are used to solve the rate equations for calculating the temporal variations of the populations in the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state in different crystals. The calculated result agrees with the measured variation of the uv emission (${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}\to {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}+{}_{}{}^1{}_{}{}^{}I_6^{}{}_{}{}^{}$, 393 nm).