Plasmonic and Photonic Modes in Colloidal CuS Nanocrystals

Abstract Copper monosulfide (CuS), also known as covellite, displays exceptional optoelectronic characteristics, exhibiting both plasmonic and photonic absorption in its monolithic nanomaterial form. It is classified as a hybrid metallic‐semiconducting material and a natural hyperbolic material with a distinctive crystal structure. Nanostructured CuS has been demonstrated to support localized surface plasmon resonances (LSPR) in the near‐infrared spectral range. Here, the phenomenon of near‐infrared (NIR) to visible electromagnetic field localization in ultrathin crystalline quasi‐2D CuS nanocrystals is revealed. This is achieved by mapping LSPRs in a range of CuS structures using high‐resolution electron energy‐loss spectroscopy in combination with cathodoluminescence spectroscopy. In addition to LSPRs, a range of photonic modes in the visible and ultraviolet spectral ranges is identified in colloidally defined single‐crystalline nanostructures, with numerical simulations providing supporting evidence. Finally, CuS nanocrystals exhibit visible NIR light emission within the range of 600–900 nm when excited by an electron beam. Altogether, these properties make CuS nanocrystals highly suitable for applications in telecommunications, sensing, and nanophotonics.