Hydrogen-related conversion processes of Ge-related point defects in silica triggered by UV laser irradiation

The conversion processes of Ge-related point defects triggered in amorphous SiO2 by 4.7 eV laser exposure were investigated. Our study has focused on the interplay between the O=Ge•-H H(II) center and the twofoldcoordinated Ge defect O=Ge••. The former is generated in the post-irradiation stage, while the latter decays both during and after exposure. The post-irradiation decay kinetics of =Ge•• is isolated and found to beanticorrelated to the growth of H(II), at least at short times. From this finding it is suggested that both processes are due to trapping of radiolytic H0 at the diamagnetic defect site. Furthermore, the anticorrelated behavior is preserved also under repeated irradiation, light at 4.7 eV destroys the already formed H(II) centers and restoretheir precursors =Ge••. This process leads to repeatability of the post-irradiation kinetics of the two species after multiple laser exposures. A comprehensive scheme of chemical reactions explaining the observed postirradiationprocesses is proposed and tested against experimental data.