Various uv and vacuum-uv optical-absorption bands found in as-manufactured high-purity SiO2 glass were studied. Two types of absorption bands were found near 5.0 eV, one of which is attributed to the oxygen vacancy (?Si-Si?). The absorption band at 7.6 eV is also found to be caused by the same oxygen vacancy. Observation of the decay lifetime of photoluminescence and calculations using the ab initio molecular-orbital program show that the 7.6-eV band is caused by a singlet-to-singlet transition, while the 5.0-eV band is caused by a singlet-to-triplet transition.
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