Knowledge Bank

Using a mode-locked argon-ion laser and a time correlated single photon counting detection system, fluorescence lifetimes were measured for two carbocyanine sensitizing dyes in gelatin and adsorbed to AgCl and AgBr microcrystals. The dyes studied, $3,3\prime$ -diethyloxathiacarbocyanine (OC-THC) and $3,3\prime$ - diethyloxathiacarbocyanine (THC), both showed large decreases in fluorescence lifetimes as they went from a gelatin environment to the surface of either silver halide, with the decreases being most pronounced on silver bromide. From these data, rate constants $ks$ for sensitization of the silver halide photographic response by the lowest excited singlet states of the dyes were calculated. These rate constants are in the range of $109-1010sec-1$ and for a given dye, are larger on AgBr than AgCl. On the same silver halide, $ks$ is larger for OC-THC than for THC.