Self-quenching of Nd3+ emission in laser garnet crystals

Abstract The emission self-quenching mechanism in Nd 3+ :YAG at low pump intensities is identified as a cross-relaxation on intermediate levels inside the system of active ions. Up to 1.5 at.% Nd 3+ this down-conversion process is a direct donor–acceptor process, without important contribution from migration and is induced by a multiple interaction picture consisting of superexchange and dipole–dipole contributions. The parameters measured from non-selectively excited global decay under 532 nm excitation at room temperature are verified by this consistent explanation of the characteristics of decay of the first-, second- and third-order Nd 3+ ion pairs that induce resolved spectral satellites at low temperatures. A further check is provided by the agreement of the experimental data on emission quantum efficiency or on fractional thermal load with those calculated by using the characteristic parameters of the energy transfer determined in this work. It is thus shown that self-quenching of emission is a limiting factor for the quantum efficiency of Nd 3+ :YAG. The extension of the theoretical formalism based on a discrete, random and equiprobable occupation of crystallographic sites by Nd 3+ ions, used in the analysis of down-conversion to the case when up-conversion is also present is discussed.