Ionic conduction of silver bromide emulsion grains as affected by dye adsorption

The effects of various dyes upon the electrical conductivity of cubic silver bromide grains with edge lengths of 0.9 μm in a photographic emulsion have been studied with the aid of dielectric loss measurements. The conductivity of the grains was increased by 3,3′-diethyl-9-methylthiacarbocyanine bromide (dye 1) and 1,1′-diethyl–2,2′-quinocyanine iodide (dye 2), and decreased by erythrosin (dye 3) and a merocyanine (dye 4). Based on the knowledge that dyes 1 and 2 are tightly attached to positively charged surface sites composed of silver ions, and that dyes 3 and 4 to negatively charged surface sites, the results are considered to provide evidence for the view on the formation of interstitial silver ions through the positively charged surface sites on silver bromide microcrystals.