Optical transitions in neutron-irradiated MgAl2O4 spinel crystals

Neutron irradiation of MgAl2O4 spinel crystals produces an F-center absorption band in the uv accompanied by a broad absorption band in the visible region. Excitation and emission experiments identify the observed structure in the visible absorption band as optical transitions of transition-metal impurity ions perturbed by neighboring F centers. The perturbation of the F center increases the oscillator strengths for these transitions by more than 3 orders of magnitude. The results of these experiments suggest that the 480-nm emission band, previously attributed to the F center, is also due to a transition-metal impurity