Dynamical Studies of Color Sensitization in Photography

首次在飞秒时间尺度上研究了溴化银纳米晶的光谱增感和超增感。测量了染料1吸附在不同形状(立方体和八面体)的溴化银纳米晶(边距40~900 nm)上的J-聚集体的无湮没荧光。观察到了非常快的非指数荧光衰减，其快分量从0.4到2.5ps，平均衰减时间从1.1到5.5ps，这取决于AgBr颗粒的类型和大小。立方体颗粒的平均荧光衰减时间是八面体颗粒的数倍。通过时间分辨荧光各向异性测量，研究了J-聚集体在八面体AgBr微晶体上的超快激发能量转移。各向异性衰变是两相的，两个时间常数分别为~0.15ps和2-7ps。短时间常数几乎与染料覆盖率无关，而第二个时间常数在较高的染料覆盖率时变慢。在第一次电子注入AgBr0.7ps之前，在{111}表面上外延排列的J-聚集体之间发生了超快激发转移(0.1ps)。

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).