The emission of photons when the surfaces of metals, semiconductors, ionic crystals, and glasses are bombarded by 5 to 8 ke V argon ions has been studied by spectroscopic analysis. The conditions for the resonance transfer of an electron between a metal and an ionized or excited atom at small distances from the surface are examined and applied to the sputtered particles of the various materials. It is established that these conditions govern the light emission from the low‐energy sputtered particles of metals and are also to some extent applicable to semiconductors. For insulators, however, the radiation appears to come only from excited sputtered atoms.