Abstract

The interaction of excited electrons and holes with defects in network semiconducting and insulating glasses is examined. Of particular interest is the diffusion of vacancy sites in oxide materials that can aggregate to form voids and eventually lead to the formation of nanoscale bubbles. This is a process that is known to occur in nuclear waste materials, but the mechanisms remain unclear. A radioactive decay event can release energy in the keV to MeV range that is dispersed amongst the emission of alpha-particles, beta-particles, and gamma rays (depending upon the radionuclide), and into the momentum of the remaining ion. The particle emission lead primarily to electronic excitation energies and self-trapped excitons, whereas the momentum on the ion leads to a recoil cascade. These processes lead to an abundance of bond breaking and topological rearrangement. During the lifetimes of these events, defects such as vacancies, peroxides and E’ centers are formed, and also leads to the etching and formation of molecular oxygen. The underlying physics and chemistry of these processes are studied using a semi-empirical methodology specifically designed to examine amorphous networked materials. The method can be implemented in parallel to study large system sizes as required in the simulation of recoil cascades, and contains enough electronic information to model excited states that lead to the formation of excitons. An overview of the model approach and its application for determining the diffusion barriers of defects in the presence of excitons will be discussed.

© 1997 Optical Society of America