No abstract

Photocurrent transients are studied on freshly cleaved and photooxidized anthracene crystals using blocking contacts. Holes are generated by singlet excitons dissociating at surface states (electron traps) and via exciton–exciton interaction, while electrons are produced only via the latter process. The first process will reach a state of saturation at high intensities if the surface states are almost completely filled by electrons during one light pulse. Spacecharge effects occur only in highly photooxidized samples. With this model the peculiar intensity dependence of photocurrents can be explained without invoking bimolecular charge carrier recombination.

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No abstract

The growth of hole yield and the reduction of fluorescence yield during surface photooxidation were studied on anthracene crystals. A nonlinear correlation between fluorescence quenching and enhanced hole generation is found. It is concluded that at least two types of surface states are formed by photooxidation: one type which quenches singlet excitons and which is a precursor of the other type which quenches excitons and, at the same time, induces hole generation. Two illustrative alternative models are discussed. The type‐two states are most probably anthraquinone molecules.