Properties of photoexcited holes in silver bromide crystals

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Abstract
The development of a sensitive method for the detection of holes in silver bromide crystals has made possible the study of their properties. The method is based on the destruction of a thin deposit of silver by the bromine formed when photoexcited holes migrate to the surface of a silver bromide crystal. The application of a photographic developer allows the quantitative determination of 1015 holes per cm2. Different variants of this method have been applied to measure the lifetime and the drift mobility of photoholes, well as their dependence on the temperature. The diffusion coefficient at room temperature was also evaluated. All results pertaining to the properties of holes in silver bromide seem to fit a unified interpretation if one assumes that free holes generated on exposure are soon neutralized to form rather stable complexes. The fate of photoholes is further discussed in view of the theory of the photographic process. It is assumed that the recombination between an electron and a hole is very unlikely. In spite of that, it is argued that the silver of the latent image can still be destroyed as a result of the diffusion of neutral hole complexes. The building of a stable latent image therefore seems possible only in the presence of sensitizers. These were shown to act aa bromine acceptors, binding holes irreversibly. Gelatins appears to be inefficient in this respect.

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