Excitons in the Surface of Aromatic Hydrocarbon Crystals Studied by Biphotonic Electron Emission

Abstract

The dynamics of excitons in the surface region has been studied with five aromatic hydrocarbon crystals, anthracene, pyrene, fluoranthene, coronene, and α-perylene through electron emission which occurs through excitonic processes. Fusion (annihilation) and photoionization of excitons have been found to be the major processes which lead to the emission, although there are indications of the participation of other less important processes. Factors determining the dominant process under a specific condition are discussed. The lifetimes of the excitons in the surface region of crystals of anthracene, pyrene and fluoranthene are found to be the same as those in the bulk, while shorter lifetimes have been found in crystals of coronene and α-perylene. Quenching by adsorbed oxygen is proposed as the origin of the difference in the behaviours.