Triplet Excitons in Anthracene Crystals—A Review

Abstract

The investigation of optically generated triplet excitons in anthracene crystals began in 19633 with the discovery that red light from a ruby laser can generate detectable concentrations of triplet excitons in spite of the low probability for this transition. Following this discovery, experimental and theoretical studies of triplet excitons became a much more active area of research in teh field of the organic sold state. Anthracene has been chosen as the organic solid state. Anthracene has been chosen as the model system by the vast majority of the investigators. For this reason this review deals with anthracene almost exclusively. We, furthermore, emphasize the work at room temperature where the triplet excitons are essentially free and where understanding of their properties has progressed the farthest. Only brief mention will be made of low temperature experiments where complicated trapping effects play an essential role, and a great deal of additional research is necessary for gaining a clearer understanding of what is goind on. Although the literature was surveyed to the end of 1967, a few 1968 papers are included. In keeping with our own interests, we will stress dynamical properties in this paper.