Concentration growth and thermal stability of γ-ray induced germanium lone pair center in Ge-doped sol-gel a-SiO₂

We report an experimental study of the concentration growth by γ-ray irradiation of germanium lone pair center (GLPC) in 10⁴ part per million molar Ge-doped sol-gel silica. The data show that γ-ray induced GLPC concentration increases linearly up to ∼5 MGy and then it seems to reach a limit value. In addition to the dose dependence, we have studied the thermal stability of the radiation induced GLPC in ambient atmosphere up to 415 °C. We found that the concentration of this latter GLPC starts to decrease at ∼300 °C, at variance to native GLPC, suggesting that the annealing is related to irradiation products. After the thermal treatments the photoluminescence (PL) activity of the γ induced GLPC shows some spectroscopic differences with respect to that related to the native. These differences have been investigated both as a function of excitation energy and by recording the photoluminescence time decay at low temperature. The obtained results are interpreted on the basis of thermally induced changes in the environment of the defect.