The temperature dependence of Cr³⁺photoluminescence in some garnet crystals

Abstract

The temperature dependence of Cr3+ photoluminescence has been measured in the garnets Y3Ga5O12, Gd3Sc2Al3O12 and Gd3Sc2Ga3O12. The observed intensities in the 2Eg to 4A2g and 4T2g to 4A2g 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 2Eg and 4T2g 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.