Concentration quenching in fine-grained ceramic Nd:YAG.

We have studied the concentration dependent fluorescence decay kinetics of ceramic Nd:YAG, to resolve inconsistencies in the previous literature. Our data indicate that earlier reports of single exponential lifetimes even at Nd concentrations of a few percent were due to the effects of long-pulse excitation. Under short-pulse excitation the fluorescence decay is nonexponential for concentrations greater than about 1% atomic. Energy migration to sinks consisting of cross-relaxing Nd ions dominates at long times, whereas single-step energy transfer to randomly distributed quenching sites dominates at earlier times. The concentration dependence of this single-step transfer indicates direct cross-relaxation between individual ions at concentrations below 4% atomic, but resonant transfer to quenching sites consisting of Nd pairs at higher concentrations.