Luminescent Emission from an Organic Solid with Traps

On the basis of a nearest-neighbor random-walk model for exciton propagation, we calculate the timedependent luminescent emission from an organic phosphor containing exciton traps. For the situation in which the traps themselves also emit a characteristic luminescence, we also calculate the time dependence of that luminescence. The results agree qualitatively with recent measurements of the time dependence of the fluorescence of tetracene-doped anthracene; detailed comparison yields reasonable values for the lifetime of each phosphor and for the time the anthracene singlet exciton spends on one site. There is no need to postulate a long-range energy-transfer mechanism.