Hot Electrons and Electromagnetic Effects in the Broadband Au, Ag, and Ag-Au Nanocrystals: The UV, visible, and NIR Plasmons

Energetic and optical properties of plasmonic nanocrystals strongly depend on their sizes, shapes, and composition. Whereas the use of plasmonic nanoparticles in biotesting has become routine, applications of plasmonics in energy are still early in development. Here, we investigate hot-electron (HE) generation and related electromagnetic effects in both mono- and bimetallic nanorods (NRs) and focus on a promising type of bimetallic nanocrystal-core-shell Au-Ag nanorods. The spectra of the NRs are broadband, highly tunable with their geometry, and exhibit few plasmon resonances. In this work, we provide a new quantum formalism describing the HE generation in bimetallic nanostructures. Interestingly, we observe that the HE generation rate at the UV plasmon resonance of Au-Ag NRs appears to be very high. These HEs are highly energetic and suitable for carbon-fuel reactions. Simultaneously, the HE generation at the longitudinal plasmon (L-plasmon) peaks, which can be tuned from the yellow to near-IR, depends on the near-field and electromagnetic Mie effects, limiting the HE efficiencies for long and large NRs. These properties of the L-plasmon relate to all kinds of NRs (Au, Ag, and Au-Ag). We also consider the generation of the interband d-holes in Au and Ag, since the involvement of the d-band is crucial for the energetic properties of UV plasmons. The proposed formalism is a significant development for the description of bimetallic (or trimetallic, or more complex) nanostructures, and paving the way for the efficient application of the photophysical mechanisms based on the plasmonic HEs and hot holes in sensing, nanotechnology, photocatalysis, and electrophotochemistry.