Radiative and nonradiative transitions exhibited by Er3+ ions in mixed yttrium-erbium aluminum garnets

An investigation was made of the contribution of radiative and nonradiative transitions to the deactivation of the upper laser levels ⁴S_3/2, ⁴I_11/2 and ⁴I_13/2 of the Er³⁺ 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 ⁴I_11/2 and ⁴I_13/2 established that the quantum efficiency of the ⁴I_13/2 level was unity (to within the experimental error) and that of the ⁴I_11/2 level did not exceed 0.017. However, the possibility of using high activator concentrations made the laser utilizing the ⁴I_11/2–⁴I_13/2 transition sufficiently efficient.