Population dynamics inEr3+-doped fluoride glasses

A detailed study of the energy-transfer processes in ${\mathrm{Er}}^{3+}:$ flouride glasses with doping concentrations of 0.2--18 mol % is presented. Fluorescence wave forms for 11 erbium transitions were measured under 802-nm, 1.5-\ensuremath{\mu}m, 975-nm, 520-nm, and 403-nm excitation from a high-energy short-pulse source. The analysis of these data provided a physical understanding of the processes responsible for the temporal behavior of the populations of a large number of energy levels. A comprehensive nine-level rate-equation model of the ${\mathrm{Er}}^{3+}$ population dynamics in these fluoride glasses is developed. The model performs well in predicting the observed fluorescence behavior of the main fluorescing lines under all pumping conditions. The modeling process allowed 14 ion-ion energy-transfer processes that are important for the population dynamics in these fluoride glasses to be identified and their rate constants obtained. Noticeably, the inclusion of seven three-ion processes was found necessary in order to obtain good fits to the experimental fluorescence wave forms. It was also found that some three-ion processes have a significant effect on the population dynamics of the levels even in lower doping concentrations.