Defects and optical absorption bands induced by surplus oxygen in high-purity synthetic silica

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Abstract
The nature of excess oxygen in as-manufactured and γ-irradiated high-purity synthetic silicas is investigated. Electron-spin-resonance measurements suggest that peroxy radicals ( 3/4 SiOO⋅) could be produced either by the cleavage of peroxy linkages ( 3/4 SiOOSi 3/4 ) or by the reaction of E’centers ( 3/4 Si⋅) with oxygen molecules. The excess oxygen is found to exist in the glass in two forms: as peroxy linkages and as interstitial molecular oxygen. The peroxy linkage is shown to be the cause of optical absorption at 3.8 eV. Heat treatment at 900–1000 °C results in the growth of the 3.8-eV band, that is, the peroxy linkages, through the reaction of oxygen vacancies and interstitial dioxygen molecules. These results indicate that the 5.0- and 3.8-eV bands (which are characteristic of ‘‘oxygen-deficient’’ and ‘‘oxygen-surplus’’ silica, respectively) can coexist in a glass, depending on the synthesis conditions.