Optical characteristics of virgin and proton-irradiated ceramics of magnesium aluminate spinel

Intrinsic properties of optical ceramics of MgAl2O4 have been studied by means of low-temperature cathodo-, photo- and thermo-luminescence methods. Based on the excitation spectra for different emissions measured at 6 K, the UV luminescence at 4.5-5.8 eV is tentatively ascribed to bound excitons (formation energy about 7 eV) near antisite defects (cation in a "wrong" position) and electron-hole recombination in a spinel matrix. The complex UV luminescence band peaked around 5 eV undergoes thermal quenching from 6 to 200 K. The value of energy gap is experimentally estimated as 8.2 eV at 80 K. There is no saturation of the absorption connected with the radiation-induced F-type color centers at the rise of 100-keV proton fluence up to 7 x 10(17) cm(-2), while such irradiation is accompanied by the drastic suppression of cathodoluminescence, especially in UV spectral region. A further study of the origin of this luminescence attenuation still lies ahead.