EXCITON ANNIHILATION IN MOLECULAR-CRYSTALS AT HIGH EXCITON DENSITIES

Suna's kinematic equations describing exciton annihilation in aromatic crystals are solved for higher exciton densities n, i.e., where n, where is the monomolecular decay rate and is the bimolecular annihilation rate constant. It is found that in case of diffusion-limited annihilation, is a function of the exciton density n even for n small compared to the lattice site density. In general is then a monotonically increasing function of n and these density effects depend on the dimensionality of the exciton motion. For both triplet and singlet excitons, is a function of n in one-dimensional and two-dimensional systems only. In the case of singlet excitions, depends on n even in three-dimensional systems if reabsorption is a dominant mechanism of exciton motion. Some materials are suggested in which such effects could be experimentally observable. © 1979 The American Physical Society.