Ge-doping dependence of gamma-ray induced germanium lone pair centers in Ge-doped silica

We report an experimental study on the γ irradiation effects in Ge-doped sol-gel silica samples doped with Ge from 10² up to 10 ⁴ part per million molar. The samples were exposed to the radiation generated by a ⁶⁰Co source up to an accumulated dose value of 10 MGy. Our data evidence that the γ irradiation significantly increases the number of Germanium Lone Pair Centers (GLPC). Such defects are induced with a concentration that depends on the Ge content of the employed material in those samples where no optical activity related to GLPC was detected before irradiation. Furthermore an increase of the GLPC concentration was detected also in a sample that already contains this defect after the production. These findings show that, in addition to the GLPC bleaching effect already reported in the literature, γ rays can generate such defects and a range of doses exists in which the generation processes overcome the bleaching processes.