Electron-spin resonance and photographic effect of positive holes trapped by cyanine dyes adsorbed on silver bromide microcrystals

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Abstract
Electron-spin resonance (ESR) of positive holes trapped by cyanine dyes adsorbed on silver bromide microcrystals has been analyzed and correlated with their photographic effects. The ESR signal and desensitization (i.e., inefficiency in latent image formation caused by dyes) appeared in the presence of the dyes whose highest occupied levels were higher than the surface level of AgBr, which was situated 0.26 eV above the top of its valence band. Both the ESR signal and latent images formed in the presence of a cyanine dye decayed for several minutes by a second-order reaction. The activation energy of the decay was 0.4 eV, and nearly the same as the energy difference between the surface level and the highest occupied level of the dye. It is considered from the above-stated result that the desensitization was caused by the reaction between latent images and positive holes which were once trapped by the dye, and then thermally released to the surface level.

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