Visible illumination to a rhodamine B (RhB) aqueous solution containing powdery AgBr results in N -deethylation of RhB and formation of metallic Ag in AgBr. The formal quantum efficiencies for these two processes, FQE (- Et ) and FQE ( Ag ), have been measured under various conditions. In O₂-free suspensions the ratio FQE ( Ag )/ FQE (- Et ) was roughly 2. This establishes a stoichiometry of [reduced Ag⁺]/[injected electron]≅1, because single N -deethylation requires removal of two electrons from a RhB molecule. Aeration of the suspension did not affect FQE (- Et ), but significantly lowered FQE ( Ag ) due to the competition for electron capture between interstitial Ag⁺ and surface-adsorbed O₂. Doping of AgBr with Cd²⁺ influenced FQE (- Et ) in O₂-free suspensions. For nine photographic dyes, a good correlation exists between the interfacial energetics and the FQE ( Ag ) value by visible illumination; a highest value (≅8%) of the latter was found for erythrosine in an O₂-free medium. Three desensitizing dyes, methylene blue, phenosafranine, and malachite green, gave FQE ( Ag )≅0 at 580-600 nm, but suppressed the FQE ( Ag ) value at an intrinsic absorption wavelength of AgBr (435nm).