Evidence for trapped-exciton fluorescence in anthracene crystals at room temperature

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Abstract
The fluorescence variations due to imposed exciton–charge carrier interactions in anthracene are examined as a function of emission wavelength. In the short wavelength region of the emission spectrum, the observed modulation of the fluorescence intensity due to the presence of trapped charge carriers is relatively small and, with the exception of the highly reabsorbed fluorescence at very short wavelengths, is independent of emission wavelength. At longer wavelengths, however, a series of maxima develop along with a tenfold increase in the modulation. These observations are interpreted in terms of emission from trapped singlet excitons. Though the results are consistent with those expected with a discrete exciton trap at 0.43 eV, they may also be interpreted as indicating a series of exciton traps with depths in the range 0.4–1.0 eV. Results are also presented for tetracene‐doped anthracene crystals which support the hypothesis that the traps are perturbed molecules of the host crystals, rather than impurities.