Electric field dependent photoluminescence studies of nanoparticle sensitized photorefractive polymers

Electric field dependent photoluminescence studies of nanoparticle sensitized photorefractive polymer composites are reported. The composites comprise the charge transporting matrix poly(N -vinylcarbazole), the dye 1-(2′ -ethylhexyloxy)-2,5-dimethyl-4-(4-nitrophenylazo) benzene, and either CdSe or CdSeZnS core/shell nanoparticles. For the CdSe composite, application of a strong electric field causes a change in the photoluminescence intensity that continuously varies from -1% at the low energy end of the emission band to +1% at the high energy end. In contrast, the change in photoluminescence observed for the CdSeZnS composite subject to the same field is -4% across the entire spectrum. These results show that photoliberated holes recombine with negatively charged nanoparticles both by capture into the excitonic ground state and via some other nonradiative route. Further, the addition of a ZnS shell to an otherwise similar nanoparticle reduces the number of holes captured into the excitonic ground state as well as reducing the overall rate constant for recombination.