Abstract
The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light. The processes which come into play after the excitation of localized surface plasmon resonances (LSPRs) in the NPs largely determine the efficiency of the charge/energy transfer from the metal NP to the oxide. We report a study of plasmon-mediated energy transfer from mass-selected silver NPs into the cerium oxide matrix in which they are embedded. Femtosecond transient absorption spectroscopy is used to probe the dynamics of charge carrier relaxation after the excitation of the LSPR of the silver nanoparticles and to evaluate the plasmon-mediated electron transfer efficiency from the silver nanoparticles to the cerium oxide. High injection efficiencies in the 6-16% range have been identified for excitation between 400 and 600 nm. These high values have been explained in terms of plasmon-mediated direct electron injection as well as indirect hot electron injection from the NPs to the oxide. The information obtained provides an important contribution towards a knowledge-driven design of efficient cerium oxide based nanostructured materials for solar to chemical energy conversion.
Highlights
The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light
The plasmonic properties of metal NPs are strongly dependent on their size and shape
As an example we show the high-resolution transmission electron microscopy (HRTEM) image of a NP with a five-fold symmetry (Figure 1c), possibly originating from a decahedral shape and the corresponding Fourier transform with a ten-fold symmetry (Figure 1d)
Summary
The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light. 22,23 This process is possibly more efficient than the indirect transfer, where the hot electrons generated in the metal NP can be partially quenched by electron-electron and electron-phonon scattering before the injection.[6] The relative contributions of the different mechanisms depend on numerous factors such as the shape, the density and the composition of the NPs, the band structure of the semiconductor, the morphology of the interface and many more. We obtained very high electron injection efficiencies (6-16 %) that we discuss in terms of the above mechanisms, analyzing the role of the morphology of the metal NPs, of the metal/semiconductor interface, as well as the near-field light concentration effects due to hot-spot generation by the metal NPs
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