Self-quenching of Nd3+ emission in laser garnet crystals

The emission self-quenching mechanism in Nd3+:YAG at low pump intensities i s identified as a cross-relaxation on intermediate levels inside the system of active ions. Up to 1.5 at.% Nd3+ this down-conversion process is a dire ct donor-acceptor process, without important contribution from migration an d is induced by a multiple interaction picture consisting of superexchange and dipole-dipole contributions. The parameters measured from non-selective ly excited global decay under 532 nm excitation at room temperature are ver ified by this consistent explanation of the characteristics of decay of the first-, second- and third-order Nd3+ ion pairs that induce resolved spectr al satellites at low temperatures. A further check is provided by the agree ment of the experimental data on emission quantum efficiency or on fraction al thermal load with those calculated by using the characteristic parameter s of the energy transfer determined in this work. It is thus shown that sel f-quenching of emission is a limiting factor for the quantum efficiency of Nd3+:YAG. The extension of the theoretical formalism based on a discrete, r andom and equiprobable occupation of crystallographic sites by Nd3+ ions, u sed in the analysis of down-conversion to the case when up-conversion is al so present is discussed. (C) 2001 Elsevier Science B.V. All rights reserved .