Eff icient energy back transfer from Ce3+ 5d state to Pr3+ 1D2 level in Lu3Al5O12 upon Pr3+ 4f5d excitation

The step energy transfers from Pr3+ 4f5d state to Ce3+ 5d state followed by energy back transfer from Ce3+ 5d state to Pr3+ 1D2 level are studied. The Ce3+→Pr3+ energy back transfer upon Pr3+ 4f5d excitation is found to be more efficient than the normal Ce3+→Pr3+ energy transfer upon Ce3+ 5d excitation. The efficient energy back transfer is attributed to preferential excitation of the Ce3+ ion with an adjacent Pr3+ surrounding in Pr3+→Ce3+ energy transfer of the first step, whereas Ce3+ is excited randomly in the normal energy transfer. The efficiencies of Ce3+→Pr3+ energy back transfer as a function of Ce3+ and Pr3+ concentration are evaluated, respectively.