Luminescence characteristics of magnesium aluminate spinel crystals of different stoichiometry

Magnesium aluminate spinel single crystals with different stoichiometry, MgAl₂O₄ (1:1 spinel) and MgO 2.5Al₂O₃ (1:2.5) were investigated using different optical methods (cathode-, photo- and thermally stimulated luminescence (TSL), optical absorption, "creation spectra" of TSL peaks and phosphorescence by VUV radiation). Low-temperature charge carrier traps and the position of intrinsic UV emission bands depend on the degree of stoichiometry. Antisite defects (ADs), Mg²⁺ or Al³⁺ located in a "wrong" cation site (Mg|_A1 or Al|_Mg) are the main as-grown structural defects, which serve also as efficient traps for electrons and holes as well as seeds for bound excitons. AD concentration is especially high in 1:2.5 spinel. There are several manifestations of ADs (electronic excitations near ADs) in the spectral region of 7-7.5 eV, slightly below the energy gap.