Ultrafast energy transfer in J-aggregate on AgBr microcrystals: its dependence on dye coverage

The ultrafast excitation-energy transfer of the J-aggregates on the octahedral AgBr microcrystal (0.2 μm) is studied by time-resolved fluorescence spectroscopy. A rise component is observed with a time constant of about 0.1 ps. The fluorescence-anisotropy decays are biphasic with two time constants of ∼0.1 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 (0.1 ps) is suggested to take place between epitaxially arranged J-aggregates on the {1 1 1} surface prior to the primary electron injection to AgBr (0.7 ps).