Optical absorption and thermoluminescence in irradiated Mg and Ti co-doped samples was studied. Deconvolution was used to resolve the optical absorption spectra into individual Gaussian bands, and the thermoluminescence glow curve into component peaks. A preferential population of the 2.78eV optical absorption band at high ionization densities suggested that this bond could arise from a so-called 2-hit charge carrier trapping structure. A marked similarity between the thermal bleaching behavior of the single-hit 5.0eV (F-band) and the 2.78eV band led to the suggestion that the 2.78eV band arose from an F2 trapping center. This consisted of 2 adjacent anion vacancies which together captured 2 electrons.

L.Oster, Y.S.Horowitz, N.Issa: Materials Science Forum, 1997, 239-241, 733-6