Abstract

The visible extinction of noble metal nanoparticles surpasses those of semiconductor and molecular dyes by several orders of magnitude. Such superior light-harvesting characteristics are highly attractive for photocatalytic applications. Of a particular interest is the process of the plasmon near-field energy conversion, which is predicted to yield substantial gains in the photocarrier generation. Here, we employ the sample-transmitted excitation photoluminescence (STEP) spectroscopy to determine the quantum efficiency for the plasmon induced resonant energy transfer (ET) in assemblies of Au nanoparticles and semiconductor quantum dots (CdSe, PbS, etc.). The present technique distinguishes the Au-to-QD ET contribution from metal-induced quenching processes thus enabling accurate estimates of the photon-to-exciton conversion efficiency. We show that in the case of 9.1-nm Au nanoparticles, only 1-2% of the Au absorbed radiation is converted to excitons in the surrounding CdSe nanocrystal matrix. For larger, 21.0-nm Au, the photon-to-exciton conversion efficiency increases to 29.5%. The results of present measurements were used to develop an empirical model for estimating the maximum gain in the plasmon-induced carrier generation versus the mass-fraction of Au.

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