MEASUREMENT OF UP-CONVERSION ENERGY-TRANSFER PROBABILITIES IN HOY3AL5O12 AND TMY3AL5O12

The probabilities for up-conversion involving two nearest-neighbor Ho3+(I-5(7)) ions and Tm3+(F-3(4)) ions in Y3Al5O12 have been determined. The final states are I-5(5) and I-5(6) for Ho3+ and H-3(4) and H-3(5) for Tm3+. A rate-equation model has been used to obtain an expression for the concentration dependence of the up-conversion-rate constant in the migration-limited regime. We have also measured the reverse cross-relaxation probabilities for two of the processes with Ho3+(I-5(5)) and Tm3+(H-3(4)) as donors. The resuits fit well to the energy-gap law for phonon-assisted energy transfer. They also show evidence that there may be a correlation between the deviations from the energy-gap law for opposite processes.