On the question of singlet exciton diffusion in anthracene

Abstract

The time evolution of anthracene and tetracene fluorescence intensities of tetracene doped anthracene crystals was monitored as a function of tetracene concentration and temperature for samples grown by different techniques and for different methods of excitation. Singlet exciton diffusion generally invoked to explain energy transfer in this system cannot explain the observed time dependence which indicates that energy transfer is more efficient at short times than at long times. Such a variation of energy transfer efficiency is characteristic of long range resonant interaction. A combined theory of long range interaction and exciton diffusion gives a good fit to the results only if the strength of the interaction is much greater than that determined from spectral considerations. The results are independent of the method of crystal growth and of the method of excitation. The temperature dependence of the energy transfer appears to be completely contained in the variation of the anthracene decay time as temperature is lowered to 10 °K.