Ultraviolet optical properties of silica controlled by hydrogen trapping at Ge-related defects
Résumé
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 G-H bond leading to hydrogen detrapping.