Comprehensive model for sulfur sensitization

摘要

The present author has proposed a comprehensive model for sulfur sensitization, according to with monomers and diners of substitutional sulfide ions on silver halides are sulfur sensitization centers acting as positive hole traps and electron traps, respectively, while silver sulfide clusters are fog centers. The difference in oxidation potential and absorption spectrum between sulfur sensitization centers and fog centers supportd the proposed model. AS many as 500 silver sulfide clusters (i.e., fog centers) /grain (i.e., 2400/m #mu# ~2) were observed by an electron microscope in slightly fogged emulsions, indicating that the developability of each silver sulfide cluster was very low. The concentration of fog centers were independent of the amount of silver sulfide formed among variously fogged emulsions, suggesting that sulfur sensitization centers as well as fog centers were formed at surface sites, where sulfide ions were stable and liable to be coagulated. It is considered that low developability of silver sulfide clusters makes it possible to achieve high sensitivity and stability without fog formation in sulfur-sensitized emulsions. The model was successfully extended to sulfur-plus-gold sensitization centers.