X-RAY-INDUCED ABSORPTION-BANDS IN SYNTHETIC FUSED SILICAS - OH CONTENT DEPENDENCE OF INTENSITIES OF X-RAY-INDUCED ABSORPTION-BANDS IN TYPE-III FUSED SILICAS

The characteristics of X-ray-induced absorption in type-III fused silicas containing (5.8-8.7) X 10(19) cm(-3) of OH were investigated. The induced absorption spectra were decomposed into five Gaussian absorption bands at 6.5, 5.8, 5.4, 5.0 and 4.8 eV. The intensities of the 5.4 and the 5.0 eV bands decrease with increasing OH content, whereas the intensities of the 4.8 eV band increase. The OH content dependence of the 5.8 eV band is more complicated: for short irradiation times, the intensity decreased with increasing OH content, but the dependency was changed for long irradiation times. A model is proposed to explain these properties. These bands are created from two groups of precursors: the precursors of the 5.0, 5.4 and part of the 5.8 eV band are =Si-H HO-Si= structures and strained Si-O-Si bonds, while those of the 4.8 eV band and the residue of the 5.8 eV band, being dominant at long irradiation times, are H2O molecules bound to Si-OH groups by hydrogen bonds and =Si-OH HO-Si= structures.