Simple Organic Molecular Crystals

Abstract

We saw in Chap. 5 that an STE in alkali halides can be described as an excited dimer (excimer), X2− 2, on the halide sublattice, generally accompanied by off-center relaxation of the excimer ion (X− 2) relative to the excited electron wave function. Partly because of the prominent nature of STE phenomena in alkali halides and related ionic crystals, one sometimes sees self-trapped excitons characterized as a phenomenon of ionic insulators. However, the experimental study of exeimers in pure organic crystals actually predated their discovery in alkali halides by about 6yr [8.1]. The organic excimers were not commonly called self-trapped excitons until the late 1970’s, when Matsui and Nishimura showed that excimer formation in a pure organic crystal is quite naturally described within the framework of exciton self-trapping [8.2]. Some of the experimental observations on excimers to be discussed bear an interesting resemblance to phenomena in alkali halides.KeywordsLuminescence SpectrumFree ExcitonAlkali HalidePyrene MoleculeExciton LuminescenceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.