Ionizing-radiation effects in lanthanum magnesium aluminate crystals

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Abstract
Optical and electron-paramagnetic-resonance (EPR) techniques are used to study the effects of γ and electron irradiation on undoped lanthanum magnesium aluminate crystals. It has been shown that room-temperature irradiation produces a strong optical-absorption band at 400 nm associated with trapped-hole centers [J. Solid State Chem. 61, 67 (1986)]. The absorption band produced by the presence of this hole center is anisotropic with a preferential polarization anisotropy for E⊥c and the oscillator strength is found to be 0.07±0.02. The optical-absorption band can be bleached at 295 and 77 K, indicating that the excited states of the holes are close to the valence band. Polarized bleaching experiments failed to show any linear dichroism, indicating that the holes are not strongly localized at a single oxygen site. Irradiation at 77 K produces additional electron and hole centers which are presumably associated with the aluminum cations.