On the Diffusion Coefficient of Triplet Excitons in Anthracene

The experimental data of Williams and Adolf on the diffusion of triplet excitons in crystalline anthracene are analyzed within the framework of a theory which properly accounts for the diffusion of the excitons during the time of the measurement. The effect of this diffusion is to make the maximum of the delayed fluorescence appear at a longer exciting wavelength than that predicted by the theory that was used to analyze the data. It appears as if the data are consistent with a diffusion constant in the $\mathrm{c\prime }$ direction of 1.6 × 10⁻⁵ cm¹/sec, a reduction of about a factor of three from the reported value, and consistent with the value reported by Ern [V. Ern, Phys. Rev. Letters, 22, 343 (1969)].