Properties of ultrafine silver iodobromide emulsions

Three ultrafine silver iodobromide emulsions with the same iodide contents (0.3 mol%) were prepared. Their sizes were determined by transmission elect ron microscopy and X-ray diffraction, which proved that their sizes were ab out 30, 50 and 100 nm respectively. The emulsions showed the 'quantum-size effect', in that their absorption peaks shifted to short wavelengths with d ecreasing grain size and their sensitivities were far lower than those of n ormal emulsions. However, the sensitivities of these emulsions were increas ed significantly when they were reduction sensitized with (NH2)(2)CSO2, whi ch was more effective than sulphur, gold and sulphur-plus-gold sensitizatio n. The smaller the grain sizes, the better was the reduction-sensitized eff ect for these ultrafine grain emulsions. It was also observed that the ioni c conductivities were directly proportional to the surface area-volume rati o of the grains; i.e. for cubic grains the ionic conductivity was inversely proportional to the edge length of the grain, d. Similarly the photoelectr on lifetimes were directly proportional to the cubic grain edge length d. T he result of low-temperature (77 K) fluorescence also demonstrated that rec ombination of positive holes and photoelectrons increased as the grain size decreased.