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Abstract
Cubic AgIBr emulsions sensitized by sulphur-plus-gold with gold added at 40°C either before or after sulphur sensitization at 70°C were prepared and studied. Gold ions incorporate into the silver-sulphide centres and decrease the diffuse reflectance spectroscopy (DRS) response. The emulsions with gold added before the heat cycle through 70°C showed a dependence on the amount of gold for a speed increase at 0.01 s and their reciprocity failure property, whereas the emulsion with gold added at 40°C after the heat cycle did not. Gold present at the elevated sensitization temperature enhanced long-wavelength sensitivity in a wider wavelength region than gold added after the heat cycle. The different sensitometric behaviour between gold added before or after the heat cycle could be explained by the enhanced thiosulphate conversion effect of gold at 70°C. The electron trapping energy level of the sensitization centre is speculated to be slightly higher for sulphur-plus-gold than sulphur sensitization. Opposite trends were observed in DRS and long-wavelength sensitivity when the gold level increased. Whether the electronic effect of gold during exposure on top of its latensification effect in sulphur-plus-gold sensitization could be observed seems to be dependent on the sulphur level. A mechanism is proposed.