Thermal stability of gamma-irradiation-induced oxygen-deficient centers in silica

The effects of isochronal thermal treatments on three gamma-irradiation-induced point defects, named the E', ODC(II), and H(I) centers, are investigated in various types of commercial silica (a-SiO2). ODC(II) is investigated by means of photoluminescence spectroscopy, and the H(I) and E' centers by electron paramagnetic resonance. The annealing processes of the ODC(II) and H(I) center are shown to be independent of each other, and no conversion mechanisms are evidenced. In contrast, a strong similarity is observed between the annealing curves of the ODC(II) and E' centers. We tentatively ascribe the annealing processes to reactions of the defects with radiolytically formed molecules. We suggest that the H(I) center reacts with molecular hydrogen diffusing through the matrix, whereas, by analogy with results reported in the literature about the E' center, the annealing of ODC(II) is attributed to reactions with molecular oxygen or water.