Photoabsorption of the neutral oxygen vacancy in silicate and germanosilicate glasses: First-principles calculations

The photoabsorption of the neutral oxygen vacancy defects in silicate and germanosilicate glasses has been studied by first-principles quantum chemical techniques. The lowest singlet-to-singlet excitations in these defects occur around 7.0 eV, and involve promotion of an electron from a bonding orbital between the adjacent Si (or Ge) atoms to a diffuse Rydberg-type orbital. Such excitations are too high in energy to contribute significantly to the 5 eV absorption band in silicate and germanosilicate glasses.