QUANTITATIVE STUDY OF PHOTOHOLE-INDUCED BLEACHING OF LATENT IMAGE CENTERS IN AGBR EMULSIONS

The photohole-induced bleaching of latent image and subimage centers i n AgBr emulsions in the intrinsic absorption region has been studied q uantitatively by using phenosafranine dye as an effective photoelectro n scavenger. The quantum bleaching efficiencies of the minimum latent image centers in our standard development condition were thus estimate d to be typically similar to 0.8 x 10(-3)(1 x 10(-3)), -3 x 10(-3) (3 x 10(3)), and similar to 5 x 10(-3) (4 x 10(-3)), respectively, for pr imitive, S-sensitized, and S + Au-sensitized emulsions consisting of 0 .4 - 0.53-mu m cubic (0.55-mu m octahedral) grains. A much higher quan tum bleaching efficiency of similar to 1 x 10(-2) was measured for wha t we identified with a two-atom subimage center. The hole-induced blea ching efficiency measured in this way correlates well but inversely wi th the energy gap between the highest occupied level of the center to be bleached and the valence band edge that can be derived from the cor responding photoionization threshold independently measured elsewhere. The observed energy-gap dependence suggests that the quantum bleachin g efficiency is controlled kinetically by hole capture cross section t hat increases with decreasing hole-trapping depth, as expected for non radiative, multiphonon processes. The present study also provides addi tional evidence to support that S + Au-sensitized grains allow latent image centers both with and without built-in gold atoms to form under high-intensity exposure.