http://worldcat.org/entity/work/id/137289815

Photoelectronic processes and a search for exciton mobility in pure and doped alkali halides

A search has been conducted for evidence of exciton motion in the alkali halides. Two types of experiments were performed. In both sets of experiments diffusion of photon-created excitons to some 'detector' whose output could be monitored was looked for. In the first type of experiment the detector was a thin film on the surface of the alkali halide in which the excitons were created. The energy level structure of the film was such that the exciton energy of the bulk alkali halide was energetically sufficient to excite and eject an external electron from the film. The other type of experiment was done with iodine atoms substituted in KCl and KBr crystals. These iso-electronic impurities have localized excitonic states which are ionizable at 300 degrees K. The idea was to create excitons which might wander to an iodine site and then excite the state which thermally ionizes, producing a photocurrent. The quantum yield of the photocurrent excitation process was measured as a function of the iodine concentration. It is concluded that the experiments indicate a prompt relaxation of the exciton into some self-trapped state, probably a v sub k -type state as has been predicted by Wood. It is shown, using some of the analysis developed to interpret these experiments, that previous experiments, thought to have indicated exciton mobility, are in fact consistent with the relaxation model. (Author).

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