Ultraviolet optical properties of silica controlled by hydrogen trapping at Ge-related defects

We studied the effects induced by the ultraviolet-laser and -lamp exposure sequences on the twofold coordinated germanium (Ge^∙∙) and the H(II) center (Ge^∙H) in silica. The H(II) centers, generated after the first laser irradiation stage by the trapping of atomic hydrogen H⁰ at the (Ge^∙∙), are destroyed by the subsequent lamp exposure with efficiency depending on photon energy. The H(II) photodestruction is activated from ∼4 eV, and its cross section is here quantitatively measured, so giving the absorption profile of this center. Consistent with the observed correlated recovering of (Ge^∙∙), the photodestruction is mainly due to the photolysis of the GeH bond leading to hydrogen detrapping.