DECAY OF EXCITONIC GRATINGS - EFFECT OF EXCITON DIFFUSION AND REABSORPTION OF EXCITON FLUORESCENCE

A phenomenological theory of the decay time of an excitonic grating (a grating of exciton densities) formed at some initial moment in a plane-parallel plate of a molecular crystal has been developed. Along with the diffusion of excitons reabsorption of the fluorescence light radiated by excitons is also taken into account. It is shown that in crystals with large overlapping of absorption and emission spectra the life time of the exciton grating is diminished appreciably by reabsorption. Numerical estimations for this life for anthracene at room temperature were made. In the above conditions it is the reabsorption which is important, whereas the diffusion of excitons hardly affects the decay time of the excitonic grating. The available experimental data and possible trends of further investigations are discussed.