Review of Luminescence Studies on Latent Image Formation in Silver Halide Emulsions

Abstract

Certain impurity centers that appear on chemical sensitization of photographic emulsions are shown to induce new photoluminescence (PL) bands of emulsion microcrystals at low temperature, as well as to control photographic properties at room temperature. The nature and function of these centers has been investigated using PL. We found that temperature quenching of some PL bands occurs by an ionic mechanism, specifically neutralization of electrons localized on the recombination center by mobile silver ions in competition with radiative recombination of holes and electrons. Thus, PL and latent image formation appear to be competing processes.We have also observed the appearance of new PL bands in near infrared (IR) spectral regions as a result of sulfur sensitization and have shown that (Ag2S)n clusters of different sizes determine this PL. Further, it has been shown that small clusters are hole traps and that large, mixed (Ag2S)p Ag+k clusters are the centers of photosensitivity. Formation of (Ag2S)n and mixed (Ag2S)p Agk+ clusters during sulfur sensitization and Agm0 clusters during reduction sensitization involves silver ions from surface layers of the emulsion microcrystals. This process is accompanied by an increase in structural defects, so that the concentration of uncompensated surface Brs− and Is− anions increases. These anions are hole traps. Thus, we conclude that during chemical sensitization, hole trap centers are formed but their origin is not necessarily silver or silver sulfide.