On the origin of the 5.0 and 7.6 eV absorption bands in oxygen deficient alpha-quartz and amorphous silica. A first principles quantum-chemical study

We have studied the electronic structure and the optical transitions of point defects in cr-quartz and amorphous silica by means of cluster models and all electron configuration interaction (CI) calculations. A series of diamagnetic defects has been studied. For each center a full geometry optimization has been performed at the Hartree-Fock level of theory. Electronic transitions to the lowest excited states have been computed by performing extensive CI calculations. We found that the 7.6 eV absorption band experimentally observed in the optical spectrum of oxygen deficient silica is due to a single oxygen vacancy. Electronic transitions from a double oxygen vacancy and a two-coordinated Si are also considered in view of their potential role as the origin of one component of the 5.0 eV absorption band. (C) 1997 Elsevier Science B.V.