Effect of I− impurity on the efficiency of silver cluster formation on AgBr microcrystal surfaces

Computer simulation is used to study the effect of iodide impurity on silver cluster formation on AgBr microcrystals. The simulation is based on a nucleation-and-growth model of silver cluster formation in competition with recombination of electrons and holes. The efficiency of silver cluster formation is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. This behavior is due to a partitioning of the hole between free and trapped states which favors the free side as size increases. As a result, recombination decreases and efficiency increases at large microcrystal size. Iodide impurity decreases efficiency relatively more at larger sizes because it introduces an internal recombination pathway not present in the control simulation. Because of their larger volume-to-surface-area ratios, the larger microcrystals are affected more by this additional recombination pathway than smaller microcrystals.