Vacuum ultraviolet optical absorption band of non-bridging oxygen hole centers in SiO2 glass

An intense broad vacuum ultraviolet (VUV) optical absorption band with peak at 6.8 eV and halfwidth ≈1.7 eV is identified in irradiated glassy SiO2 and assigned to dangling oxygen bonds (non-bridging oxygen hole centers, NBOHC). It was selectively created by photolysis of silanol (SiO–H) groups by 7.9 eV photons of F2 excimer laser at low temperature. Subsequent analysis by VUV absorption, time-resolved luminescence, and electron paramagnetic resonance spectroscopies during thermal annealing showed an exact correlation to the well-known 4.8 and 2 eV absorption and 1.9 eV luminescence bands of NBOHC. The estimated oscillator strength of the 6.8 eV band is f≈0.05. This band may be one of the dominant causes of VUV optical absorption induced by excimer-laser irradiation of silica.