Optical spectra of MgAl2O4 crystals exposed to ionizing radiation

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Abstract
Exposure of MgAl2O4 crystals to 137Cs γ rays produces a broad absorption complex centered near 3 eV and at the same time destroys absorption at 4.8 and 6.4 eV which is attributed to charge transfer transitions on octahedral Fe3+ impurity ions. Thermal and optical bleaching of the 3‐eV absorption complex in crystals with different Fe3+ concentration reveal that this complex is composed of absorption bands located at 2.8, 3.1, 3.6, and possibly at 3.9 eV. Analysis of the intense, persistent afterglow and conductivity after γ‐ray exposure and thermally stimulated conductivity discloses a very high concentration of shallow electron traps with a prominent set of these traps having a thermal depth of ∼0.9 eV. It is proposed that antistructure disorder, e.g., Al3+ ions on tetrahedral sites, is responsible for a substantial portion of these electron traps.