(n = 3) and Ho 3+ (n = 10) with average decay times in the order sub-ms that can be related to a non-negligible impact of cross-relaxation of the radiatively emitting levels. The low cutoff phonon energy of only 700 cm -1 implies a limited capability for multiphonon relaxation, which explains why the investigated single-crystalline Nd 3+ -and Ho 3+ -activated In-based garnets still show appreciable photoluminescence brightness.