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Abstract
Two types of silver halide emulsion microcrystals of different sizes (nanometre and micrometre) were prepared by the double-jet method. Their light absorption spectra in the visible light region showed that the light absorption of ultra-fine silver iodobromide emulsion microcrystals with an average diameter of 30 nm was quite low compared with conventional cubic emulsion grains with an edge length of 0.2 μm. The low light absorption of the ultra-fine silver iodobromide emulsion microcrystals was effectively improved by the addition of a sensitizing dye for blue light. As a dopant for trapping positive holes, formate was incorporated into the ultra-fine silver iodobromide emulsion microcrystals, by which the photosensitivity was significantly enhanced. The photosensitivity of the ultra-fine silver iodobromide emulsion microcrystals was further increased by dye sensitization or sulphur, together with dye sensitization after formate doping. The results indicated that combined sensitization of formate dopant together with a sulphur sensitizer and sensitizing dye for blue light can be favourable for latent image formation with high efficiency. It provided a feasible way of improving the sensitometric property of ultra-fine silver iodobromide emulsion microcrystals.