Optical absorption properties of TiO2-doped silica glass in UV–VUV region

Optical absorption properties of TiO2-doped and non-doped silica glass (type I) were studied to investigate the effect of titanium (Ti) ion doping on absorption spectra changes produced by 7.2 eV irradiation. The samples were prepared by polishing down to a thickness of about 100 μm to resolve the absorption bands in the VUV range and to measure the color center created or eliminated in the irradiated surface region. For both kinds of silica glass, the magnitude of the 7.6 eV absorption band of a thin sample (<100 μm) decreased at the early stage of irradiation, while that of the 5.8 eV absorption band increased. In the thick sample (>100 μm), the 7.6 eV band magnitude increased even in the early stages of irradiation. These results indicate that the type I silica glass absorbs <7 eV light, which is much smaller than band gap energy of SiO2 glass, and produces Si–Si bonds. The magnitude of these changes were smaller in the TiO2-doped silica glass. The molar extinction coefficients of TiO2 in silica glass were determined in the 4.0–8.0 eV range by using 47–150 wt ppm Ti containing samples. To avoid perturbation by absorption due to Si–Si bonds, the samples were heated at 950 °C in hydrogen atmosphere. Two absorption maxima were observed at 6.2 and 7.6 eV, and the corresponding molar extinction coefficients were estimated to be 3.0 × 104 and 5.5 × 104 L mol−1 cm−1, respectively. The 7.6 eV absorption in the TiO2 doped samples prevents bond breaking by VUV photon for type I silica glass.