Impact of metallic nanoparticles on photoinduced fluorescence enhancement of colloidal quantum dots.

摘要

We studied emission of colloidal semiconductor quantum dots in the presence and absence of metallic nanoparticles as they were irradiated with a laser beam. For this, we first used numerical calculations to find extinction coefficients of different types of metallic nanoparticles. Gold metallic nanoparticles were then fabricated with two techniques: i) thermal evaporation of gold thin film on a substrate followed by thermal annealing, and ii) electron beam lithography. The sizes of the metallic nanoparticles were optimized to achieve significant amount of plasmonic enhancement of quantum dots emission. Our results show photo-induced fluorescence enhancement of CdSe/ZnS quantum dots can be dramatically suppressed in the presence of metallic nanoparticles. Additionally, we demonstrate at a certain intensity of the laser field the emission of the quantum dots rolls over, making the quantum dots quite inefficient emitters. We showed such processes were caused by plasmonic near field enhancement of the metallic nanoparticle and sudden activation of photoionization process.