Interstitial oxygen molecules in amorphous SiO2. I. Quantitative concentration analysis by thermal desorption, infrared photoluminescence, and vacuum-ultraviolet optical absorption

The amount of oxygen molecules (O2) in amorphous SiO2(a-SiO2), also called interstitial O2, was quantitatively measured by combining thermal-desorption spectroscopy (TDS) with infrared photoluminescence (PL) measurements of interstitial O2 at 1272 nm while exciting with 1064-nm Nd: yttrium aluminum garnet laser light. It was found that the amount of O2 released by the TDS measurement is proportional to the intensity decrease of the PL band, demonstrating that a-SiO2 easily emits interstitial O2 during thermal annealing in vacuum. This correlation yielded the proportionality coefficient between the absolute concentration of interstitial O2 and its PL intensity normalized against the intensity of the fundamental Raman bands of a-SiO2. This relationship was further used to determine the optical-absorption cross section of the Schumann–Runge band of the interstitial O2 located at photon energies ≳6.5eV. This band is significantly redshifted and has a larger cross section compared to that of O2 in the gas phase.