On the Role of Silver Molecules in Photographic Sensitivity

Abstract

Ag² molecules in silver halide crystals have three functions in the mechanisms of photographic sensitivity. (I) They introduce donor centres which are dissociated by the annihilation of photons or of excitons of polarization waves and excited dye molecules. These processes produce conduction electrons and centres which dissociate into interstitial silver ions and silver atoms. The atoms dissociate after thermal activation. Tivo conduction electrons and two interstitial silver ions are thus made available for latent image formation. (2) They provide latent image growth nucleus precursors at which conduction electrons and interstitial silver ions combine to give Ag₃ clusters. These adsorb a silver ion from an adjacent site to give latent image growth nuclei. Positive holes are created by the annihilation of photons and excitons at these and other acceptor centres. (3) The Ag² molecules then provide effective traps for positive holes giving centres which dissociate as above. Silver atoms are released in both (1) and (3) which have a lifetime of about 1 sec at room temperature before dissociation. This means that, subject to environmental regressive processes, post-exposure latent image< growth can occur with (1) and (3) in reduction sensitized systems.