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 B${}_2$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.