Carrier Generation and Recombination in Anthracene

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Abstract
The hole—electron recombination coefficient, 2–3×10−6 cm3/sec, in anthracene has been determined directly by observing the decay of photogenerated carriers as a function of time. From considerations of the magnitude of the recombination, it is concluded that carrier generation can be observed only after excitation to an almost free electron band above the lowest narrow tight-binding band. The experimental data of Castro and Hornig, and Kearns, are analyzed in terms of band-to-band transitions to this upper band. From considerations of the wavelength dependence, autoionization of the Frenkel exciton levels at these energies is shown not to be important. Theoretical considerations predict a very small quantum yield for the band-to-band transition. A small cross section is consistent with experiment.