FLUORESCENCE LIFETIMES AND SENSITIZATION RATE COKSTAHTS FOR DYES ABSORBED TO SILVER HALMDE MICROCRYSTALS

Author Institution: Eastman Kodak Company, Research LaboratoriesUsing 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 $k_{s}$ 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 $10^{9}-10^{10} sec^{-1}$ and for a given dye, are larger on AgBr than AgCl. On the same silver halide, $k_{s}$ is larger for OC-THC than for THC