An investigation was made of the contribution of radiative and nonradiative transitions to the deactivation of the upper laser levels 4 S 3/2 , 4 I 11/2 and 4 I 13/2 of the Er 3+ ion in mixed yttrium-erbium aluminum garnets. The optimal activator concentrations, ensuring minimum concentration quenching of the luminescence, were determined. A comparison of the Einstein coefficients, deduced from the corresponding integrated absorption coefficients, with the experimentally determined room-temperature lifetimes of the levels 4 I 11/2 and 4 I 13/2 established that the quantum efficiency of the 4 I 13/2 level was unity (to within the experimental error) and that of the 4 I 11/2 level did not exceed 0.017. However, the possibility of using high activator concentrations made the laser utilizing the 4 I 11/2 – 4 I 13/2 transition sufficiently efficient.
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Basiev et al. (1976) studied this question.