Abstract: The doping effects of Pb²⁺ on electric and photographic properties of iodobromide emulsion microcrystals were investigated in this paper.The technique of dielectric loss, microwave photoconductivity and electron microscope were used to determine the ionic conductivity, photoconductivity and the size of microcrystals of the emulsion doped respectively. The results indicate that Pb²⁺-doping causes the decrease of photographic sensitivity, the increase of fog and a great decrease of photoconductivity, but the size of crystals and ionic conductivity are shown to be changed only a bit.The change of sensitivity properties of the emulsion doped can probably be explained by the following two reasons: (1) Pb²⁺ ions act as deep traps, greatly decreasing photoconductivity of the emulsion microcrystals. (2) Pb²⁺ (or PbBr2) functions as a recombination center and catalyze the development, increasing fog formation.

Key words: photographic chemistry, silver iodobromide emulsion, ionic conductivity, photoconductivity, Pb²⁺-doping