The temperature dependence of Cr3+photoluminescence in some garnet crystals

The temperature dependence of Cr 3+ photoluminescence has been measured in the garnets Y 3 Ga 5 O 12 , Gd 3 Sc 2 Al 3 O 12 and Gd 3 Sc 2 Ga 3 O 12 . The observed intensities in the 2 E g to 4 A 2g and 4 T 2g to 4 A 2g emission transitions are interpreted using a model based on the effects of small changes in unit-cell size on energy level shifts due to variations in the strength of the octahedral crystal field. Such changes in unit-cell length are produced by either crystal non-stoichiometry or thermal expansion. The effect of thermal expansion is to reduce the energy level splitting between 2 E g and 4 T 2g excited states with increasing temperature. In garnets where this splitting is small, spin-orbit admixture of these levels produces measurable changes in the emission band shape and radiative decay time at low temperatures.