Exciton Self-Trapping and Lattice Defect Creation in Rare Gas Solids and Other Insulators

Abstract

We have studied the possible creation of stable lattice defects induced by exciton self–trapping (STE) in solid neon. Generally speaking, the STE–bubbles accompanied with a plastic deformation are found to be at lower energies than a pure STE–bubble. Those with two vacancies in the first atomic shell have the lowest energy. Some of the vacancy–interstitial atom pairs escaped mutual annihilation as the electronic sub–system returned to the ground state, thereby stable lattice defects resulted. The emission energy changes of lattice defect–associated STE have been evaluated and are found to be in reasonable agreement with observed data. Much has been learned recently on the role of the STE in radiation damage creation of ionic halides. We have made a brief comparison of the ionization induced defect formation processes in the two types of materials. In both cases, the excited electron is the prime driver of the process. In solid neon the excited electron is directly attracted to the localized hole on Ne, but repelled by the ground state Ne atoms. In the halides the excited electron is attracted to the Madelung potential at an anion site instead. In rare gas solids, the Frenkel pair is a purely structural defect in the lattice with the electronic subsystem in its ground state. In ionic halides, the pair of F center and H center is not only an interstitial atom–vacancy pair in the halogen sublattice, but also represents an electronically excited state. Because of this difference the way the created Frenkel defects are stabilized in the two types of material is distinct.