Lattice rearrangement induced by excitons in cryocrystals

The self-trapping of excitons in atomic cryocrystals induces a variety of atomic processes including mass diffusion, and defect formation [1–4]. The basis for the physics of these phenomena is a concentration of the electronic excitation energy within a volume about that of a unit cell. Release of the energy can induce different kinds of lattice rearrangement. The above phenomena have been the subject of numerous experimental and theoretical studies on a variety of insulators [2,5–7]. Atomic cryocrystals with their simple lattice and well defined electronic structure [8] are excellent objects for investigation of exciton induced phenomena. The high quantum yield of these atomic processes caused by small binding energies in conjunction with a strong exciton-phonon interaction makes them especially suitable for experimental study. A transformation of the initial point defects involving the self-trapped excitons was observed in solid Ne by the transient absorption method [9]. The creation of new lattice defects induced by the self-trapping of excitons in atomic cryocrystals was predicted in [10]. Vacuum ultraviolet spectroscopic study revealed the formation and accumulation of permanent lattice defects generated by excitation with slow electrons in atomic cryocrystals [4,11–17]. It was supposed that the self-trapping of excitons is the stimulating factor. The first direct evidence of the exciton’s key role for the creation of radiation-induced defects was obtained in the experiments on selective excitation of solid Xe [18] and Ar [19] to the lowest exciton band Γ(3/2), n = 1. This paper reviews experiments on permanent lattice defect formation induced by electronic transitions in atomic cryocrystals. As an example recent results on local lattice rearrangement induced by the excitation of atomic and molecular states of Ar are presented.