Diffusion of Triplet Excitons in Anthracene Crystals

Diffusion of triplet excitons in anthracene crystals has been detected by time-dependent studies of the delayed blue fluorescence under varying spatial distribution of the exciting red light. The delayed fluorescence which results from triplet-triplet annihilation was used as a passive probe for detecting the triplets. The observed changes in the time dependence of the delayed fluorescence can be interpreted uniquely as due to triplet-exciton migration, and can be described by a diffusion equation. A diffusion constant of 2×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ was obtained for triplet diffusion in the $\mathrm{ab}$ plane of anthracene crystals at room temperature.