High-purity samples of silica were prepared by means of the chemical vapor-deposited soot re-melting method, and were studied by using electron spin resonance techniques after X-irradiation at temperatures of 77K or above. The spectra of the E’ center (including its 29Si hyperfine splitting), and of the triplet-state center, were measured by using 2 different detection methods. The effects of X-ray dose, thermal annealing, H treatment, and impurities were studied, and it was found that the E’ and triplet-state centers exhibited a similar dependence upon all of these parameters. This indicated that they shared a common precursor. Such centers were found only in low-OH, O-deficient samples. There did not appear to be any correlation with Cl impurities. The intensity of the 29Si hyperfine signal of the E’ center indicated that some four Si atoms were involved.

L.Zhang, R.G.Leisure: Journal of Applied Physics, 1996, 80[7], 3744-9