The time dependence of the internal structure of the charge-transfer exciton in LiF, created by an idealized point source (represented by the wavy line). The absence of significant structural changes indicates that the relative motion of the electron and hole is frozen, which demonstrates that this is a Frenkel exciton.
Exitons are a key element in the functioning of semiconductors and insulators, and understanding their structure and how they form and behave in different materials is vitally important to the development of new materials and technologies. Work at ChemMatCARS has helped settle a 70-year-old controversy about the true nature of the exciton in alkali halide insulators, the type of material in which excitons were first observed.