X-ray-induced absorption bands in type-III fused silicas

X-ray-induced absorption bands in type-III fused silicas synthesized under reducing (DR) and oxidizing (DO) conditions are investigated. In sample DR, an absorption band at 5.8 eV ascribed to the E' center ({≡}Si{·}) was induced. Photoluminescence and photoluminescence-excitation spectra suggest that the absorption band at 5.0 eV (the B₂{α} band) is caused by oxygen-deficient center ({≡}Si{·}{·}{·}Si{≡}). In sample DO, absorption bands at 5.8, 4.8, and 2.0 eV are observed. We discuss the formation mechanism of these bands based on models proposed before.