Structural imperfections in silica glasses with an optical absorption peak at 3.8 eV

Structural imperfections in silica glasses with an optical absorption peak at 3.8 eV were studied. The 3.8-eV peak was assigned to Cl2 molecules trapped in the glasses. The peak absorption was increased with increasing partial pressure of chlorine for sintering. The peak and its full width at half maxima were the same as those of Cl2 molecules in the gas phase. ≡SiOH was generated in the glasses by annealing in H2 ambient. After irradiation with a KrF excimer laser (5 eV), an absorption peak at 4.8 eV and red emission were observed. The properties were the same as the photochemical reaction of O2 molecules in the gas phase. We proposed that O2 molecules were trapped in the glass network when silica glasses were sintered under Cl2 ambient. The reaction is expressed as ≡SiOH+HOSi≡+Cl2→≡SiCl+ClSi≡+H2O↑+1/2O2 (trapped).