29Si Hyperfine structure of the E’_alfa center in amorphous silicon dioxide

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