The response of optical absorption to KrF excimer laser radiation was studied in germania-silica and alumina-germania-silica sol-gel glasses. It was found that the Al ion, in alumina-germania-silica specimens, played an important role in defect conversion under ultra-violet irradiation. Such irradiation resulted in the photochemical conversion of Ge-related O-deficient centres, with a bleaching of the optical absorption which was centred at around 5.1eV. Samples which contained Al exhibited a higher conversion efficiency of the Ge-related O-deficient centres than did those without Al.

Influence of Al Ion on Photochemical Conversion in Germania-Silica Sol-Gel Glass. A.Leyderman, H.Zheng: Journal of Luminescence, 1999, 83-84, 447-51