On the origin of the F+ centre radioluminescence in sapphire

Electron irradiation of sapphire produces primarily F centres, in marked contrast with neutron and ion irradiations where both F and F+ centres are produced. However, radioluminescence studies during electron irradiation indicate bands associated with both F and F+ centres. These emission bands show a complex dependence on dose rate and temperature. A systematic study of the radioluminescence spectra as a function of these two parameters together with optical absorption measurements indicate that the ionization of F centres is the cause of the F+ centre radioluminescence. A model describing the way the F+ emission occurs is proposed and compared with the results obtained. (orig.)