Dynamical Studies of Color Sensitization in Photography

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Spectral sensitization and supersensitization of the silver bromide nanocrystals were studied in the femtosecond timescale for the first time. An annihilation-free fluorescence from J-aggregates of dye 1 adsorbed on the silver bromide nanocrystals (edge to edge distance from 40 to 900 nm) of different shapes (cubic and octahedral) was measured [1]. Very fast non-exponential fluorescence decays were observed with a fast component from 0.4 to 2.5 ps, and an average decay time from 1.1 to 5.5 ps, depending on the type and size of AgBr grains. The average fluorescence decay time is several times longer on the cubic grains than that on the octahedral grains.By time-resolved fluorescence anisotropy measurement the ultrafast excitation-energy transfer of the J-aggregates on the octahedral AgBr microcrystal is studied [2]. The anisotropy decays are biphasic with two time constants of 〜0.15 ps and 2-7 ps. The short time constant is almost independent of the dye coverage, while the second one becomes slower at higher dye coverages. An ultrafast excitation transfer (O.1ps) is suggested to take place between epitaxially arranged J-aggregates on the {111} surface prior to the primary electron injection to AgBr (0.7 ps).