A computational study of host effects on Er3+ upconversion and self-quenching efficiency in ten garnets

A quantum-mechanical model is used to predict the energy levels and transition rates of Er in a variety of garnets in order to optimize laser performance. The existence of near resonances among the various Er manifolds as well as the transition rates are used to estimate upconversion and self-quenching of Er in ten different garnets. Morrison's quantum-mechanical point charge program for calculating crystal-field effects on rare-earth ions was used to fit experimentally determined Er:YAG energy levels obtained from the literature. Radial factors from this fit were used, along with x-ray data, to calculate theoretical levels and transition rates for Er3+ in other garnets. The calculations suggest that the crystal-field effect on the upper four levels of the ground I-4(15/2) manifold can dramatically effect resonances and thus affect upconversion and cross-relaxation processes. Additionally, a method by which they indicate how a large population density can efficiently be built up in the S-4(3/2) manifold is proposed, a necessary condition for upconversion lasing from that manifold. Based on a simple summation of cross-relaxation resonances that can contribute, LuGG is predicted to enhance this upconversion process. (C) 1996 American Institute of Physics.