Properties of ultrafine silver iodobromide emulsions

Abstract

Three ultrafine silver iodobromide emulsions with the same iodide contents (0.3 mol%) were prepared. Their sizes were determined by transmission electron microscopy and X-ray diffraction, which proved that their sizes were about 30, 50 and 100 nm respectively. The emulsions showed the ‘quantum-size effect’, in that their absorption peaks shifted to short wavelengths with decreasing grain size and their sensitivities were far lower than those of normal emulsions. However, the sensitivities of these emulsions were increased significantly when they were reduction sensitized with (NH₂)₂CSO₂, which was more effective than sulphur, gold and sulphur-plus-gold sensitization. The smaller the grain sizes, the better was the reduction-sensitized effect for these ultraline grain emulsions. It was also observed that the ionic conductivities were directly proportional to the surface area volume ratio of the grains; i.e. for cubic grains the ionic conductivity was inversely proportional to the edge length of the grain, d. Similarly the photoelectron lifetimes were directly proportional to the cubic grain edge length d. The result of low-temperature (77 K) fluorescence also demonstrated that recombination of positive holes and photoelcctrons increased as the grain size decreased.

Key Words:

• Silver iodobromide
• Emulsions
• Grain size
• Sensitivity