Use of Hydrogen Hypersensitization to Diminish Recombination and Produce Emulsion Coatings of High Quantum Efficiency

Paper presented at a Symposium on “Fundamental Problems in Photographic Science” organized by the Science Committee of The Royal Photographic Society on 8-10 September 1975 in Oxford, England.

Abstract

Loss of photographic efficiency in fine-grain, monodisperse silver bromide and silver iodobromide emulsions due to the interaction of the photoelectrons with oxygen and moisture and to recombination was largely eliminated by vacuum outgassing and hydrogen hypersensitization prior to exposure. Characteristic curves were obtained that closely fit a 2- to 3-photon theoretical curve, both in curve shape and in position on the exposure axis, for a sulphur plus gold sensitized emulsion, and a 4-photon curve for an emulsion prepared initially without deliberate chemical sensitization. Cyanine dyes with cathodic potentials in the range of -0.25 to 0.9 V and anodic potentials above 0.8 V showed no desensitization of the vacuum outgassed, hydrogen hypersensitized iodobromide emulsion, even though they strongly desensitized the untreated emulsion for exposure in air. All of the dyes were efficient spectral sensitizers for exposure under vacuum after the hydrogen hypersensitization. Without this treatment, no spectral sensitization was obtained for exposure in air, owing to severe losses of photoelectrons by recombination of trapped electrons with mobile holes and by interaction with oxygen and moisture.

Notes

Paper presented at a Symposium on “Fundamental Problems in Photographic Science” organized by the Science Committee of The Royal Photographic Society on 8-10 September 1975 in Oxford, England.