Optical Radiation from Low-Energy Ion-Surface Collisions

Impact of energetic heavy particles on surfaces gives rise to emission of optical radiation from reflected particles, sputtered particles and also from excited states of the solid. We review the present status of research in this area with emphasis on understanding the basic mechanisms which give rise to formation of excited states. The spectral line shape from ejected atoms may be analyzed to provide information on the distribution of speeds and directions of the excited species; the line intensity provides a measure of the probability for creating the state. Formation of excited species is related both to the collision processes within the solid and also to the interaction of the recoiling ejected species with the target surface. Most ejected species are atomic but important examples of ejected molecules are also discussed. Luminescence induced in the solid itself is related to recombination of electron hole pairs and is related significantly to the presence of defects.