The photolysis of small silver halide particles

Abstract

Monolayer coatings of monodisperse silver halide microcrystals of general formula AgCl x Br 1- x with 0 ≼ x ≼ 1, were prepared and measurements carried out in order to determine the efficiency of photolysis. The effect of crystal size was studied: it is well known that the speed of photographic emulsions increases with the size of the emulsion crystals. Crystal edge length was varied from 0.3─1.0 μm. It was shown that, within this range, size has no effect on the quantum yield of photolysis. The speed increase therefore arises simply because larger crystals collect more photons, and the minimum number of photons required to make a crystal developable is attained more rapidly. The effects of sensitization were studied: it was shown that the effect of gold is not to be understood purely in terms of the latent image being smaller if it is composed of gold rather than silver, but that in addition the efficiency of photolysis increases. The results of the investigation are shown to be in agreement with the Gurney─Mott model. The remarkable difference in hole self-trapping at low temperatures between AgCl and AgBr is shown to account for differences in photo­graphic behaviour.