Generation of oxygen deficient point defects in silica by γ and β irradiation

We report an experimental study of the effects of γ and β irradiation on the generation of a point defect known as ODC(II) in various types of commercial silica (a-SiO₂). The ODC(II) has been detected by means of photoluminescence (PL) spectroscopy measuring the PL band centered at 4.4 eV and excited at 5.0 eV associated to this defect. Our experiments show that ODC(II) are induced in all the investigated materials after irradiation at doses higher than 5 × 10² kGy. A good agreement is observed between the efficiencies of generation of ODC(II) under γ and β irradiation, enabling a comprehensive study up to the dose of 5 × 10⁶ kGy. Two different growth rates, one in the low and one in the high dose range, can be distinguished in all the samples examined, suggesting that the efficiency of generation of the ODC(II) depends on the dose but not on the kind of irradiation and on the dose rate. Furthermore a nonlinear dependence of the photoluminescence band amplitude on the dose D, through a power law of the kind D^α with α < 1, has been observed in the low dose range in all the materials examined.