Drift mobility, electron trapping, and diffusion-limited kinetics in sulfur-sensitized AgBr microcrystals

The room-temperature photoelectron kinetics in 1.3- and 0.4-μm AgBr octahedral emulsion microcrystals have been investigated for time scales ranging from several nanoseconds to several microseconds after exposure. Two first-order decay processes were observed in 1.3-μm octahedra. The fast process is attributable to relatively shallow electron trapping that equilibrates with thermal detrapping after ∼60 nsec; the longer decay may involve ionic processes. Sulfur sensitization of the emulsion enhanced the fast electron decay rate (decay time=14 nsec). At higher levels of sulfur sensitization, the decay rate did not change with increasing sulfur levels; such behavior can indicate diffusion-limited surface trapping. A bulk-to-surface electron drift mobility of 0.8 cm2/V sec on nanosecond time scales has been deduced from these kinetics. Implications of the data to current theories of photographic image formation and sulfur sensitization are discussed.