Modifications of optical absorption band of E'gamma center in silica

We report a study by electron paramagnetic resonance on the E0 point defect in amorphous silicondioxide (a-SiO2). Our experiments were performed on -ray irradiated oxygen-deficient materials andpointed out that the 29Si hyperfine structure of the E0 consists of a pair of lines split by 49 mT. On thebasis of the experimental results, a microscopic model is proposed for the E0 center, consisting of a holetrapped in an oxygen vacancy with the unpaired electron sp3 orbital pointing away from the vacancy in aback-projected configuration and interacting with an extra oxygen atom of the a-SiO2 matrix.