Temperature dependence of Nd3+->Yb3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal

The temperature dependence of the Nd3+-> Yb3+ energy-transfer rate in the YAl3(BO3)(4) nonlinear laser crystal has been investigated from the analysis of fluorescence decay curves recorded in the 10-600 K range. Three different regimes, independent on the dopant concentration, have been observed in the thermal behavior of the Nd3+-> Yb3+ energy-transfer rate. By comparing experimental results with theoretical predictions based on the Dexter model [J. Chem. Phys. 21, 836 (1953)], the origin of these different regimes has been explained. In addition, the influence of temperature and of both Nd3+ and Yb3+ concentrations on the Nd3+<- Yb3+ energy back-transfer rate has been also investigated, concluding that it is a migration-assisted energy-transfer process. Finally, the populations of both Nd3+ and Yb3+ metastable states achieved after continuous-wave Nd3+ excitation have been calculated and measured and results have been explained in terms of the thermal behavior of both forward- and back-transfer rates.