Effect of space charge layer on spectral sensitization in silver halide photography

The potential profile in the space charge layer with excess negative kink sites on the surface and corresponding interstitial silver ions in the interior of silver halide influences the distribution of latent image centers in it, depending on the presence of photographic stabilizers and antifoggants on its surface. In this article, the effect of the space charge layer on the spectral sensitization is explained from the following viewpoint. The electronic energy levels of a sensitizing dye molecule are higher on a negatively charged site than on a neutral site. An exciton, i.e., an excited dye molecule in a J-aggregate, migrates and injects an electron to the conduction band of silver halide more rapidly and efficiently on a negatively charged site than on a neutral site. A positive hole migrates in a J-aggregate and is kept by a dye molecule on a negatively charged site for longer time than by a dye molecule on a neutral site. It is known that the concentration of negatively charged sites is larger on octahedral grains than on cubic ones. It is then demonstrated that the above-stated viewpoints and knowledge explain the spectral sensitization phenomena. Namely, the quantum yield and rate of the electron injection by excited dye molecules for spectral sensitization are larger on octahedral grains than on cubic ones. The decay time and concentration of positive holes in J-aggregates, which are responsible for the dye desensitization, are larger on octahedral grains than on cubic ones.