Exciton Self-Trapping in Rare-Gas Crystals

Abstract

The problem of exciton self‐trapping in rare‐gas solids is investigated from a dynamical point of view. Experimental ultraviolet emission spectra from rare‐gas solids and liquids have been interpreted as arising from the radiative decay of an excited‐state dimer which becomes localized in the substance. This embedded dimer can arise from electron capture by a self‐trapped hole (R₂⁺), or by the dynamical trapping of an exciton into an excimer state (R₂*). A study of the vibrational relaxation of a molecule embedded in a solid leads to a fast trapping process in which an exciton becomes localized for all the heavy rare‐gas substances. This localization is achieved within 6 × 10⁻¹² sec by means of a resonant transfer relaxation process in which two neighboring atoms lose sufficient energy (∼ 0.5 eV) to become stabilized in a lower vibrational state of the excimer.