Excitons in aromatic crystals: Trap states, energy transfer and sensitized emission

Abstract

Traps of low concentration in molecular crystals are used as probes for studying energy transfer processes. β-halogenated naphthalene molecules in naphthalene crystals are a good system to study both the geometrical and the electronic structure of the traps. Direct trap to trap energy transfer already at relatively low concentrations is observed. Triplet exciton transport is temperature dependent, the mobility increases with decreasing temperature. This is the result of an analysis of the temperature dependence of sensitized delayed fluorescence in naphthalene-anthracene mixed crystals. Many different exciton interaction processes at high excitation densities have been studied. All attempts to observe exciton molecules or condensation of excitons in molecular crystals have failed so far. © 1976.