Structure and spectroscopic properties of trapped holes in silica

We present the first consistent comparison of the theoretically predicted structures and spectroscopic characteristics of holes trapped in crystalline and amorphous silica. The structure and spectroscopic properties of Ge and [AlO4]0 hole centers in α-quartz and self-trapped holes (STH1 and STH2) in silica glass were calculated using an ab initio embedded cluster method. The calculated principal values of g-tensor and hyperfine constants as well as the positions of maxima of optical absorption bands are in good agreement with the experimental data. In the case of Ge and [AlO4]0 hole centers, as well as STH1, the hole is almost fully localized on one O atom. In STH2 the hole is delocalized over two bridging O atoms. The calculated principal values of the g-tensor and hyperfine constants of STH1 and STH2 support the assignment based on ESR studies. The calculated optical absorption energies of one-center holes in a amorphous silica agree with the experimentally observed absorption bands assigned to STH1.