Energy Transfer in Anthracene-and Tetracene-Doped Naphthalene Crystals

Abstract

Energy transfer in thin crystals of anthracene-doped naphthalene and tetracene-doped naphthalene was investigated by monitoring the time evolution of the fluorescence intensities. The observed time dependence of the energy transfer cannot be explained by the theory of exciton diffusion generally invoked to explain energy transfer in molecular crystals. The time dependence is consistent with the predictions of long-range resonance energy transfer, but an anomalously large interaction strength is needed to fit the data. The magnitude of this interaction strength is the same for both types of impurity molecules despite the fact that there is a significant difference in the overlap of their absorption spectra with the host emission spectrum. Similar measurements were made on energy transfer from anthracene molecules to tetracene molecules in a naphthalene host. In this case, the mechanism for energy transfer is expected to be long-range resonance interaction, and it is found that the data can be fitted with the predictions of this theory using the theoretically derived value for the strength of the interaction. Thus the anomalies observed in the single-doped systems are associated only with host-sensitized energy transfer.