Abstract
Previously we showed that the optical properties of Cu2O crystals are facet-dependent by examining Au‒Cu2O core‒shell nanocubes, cuboctahedra, and octahedra with octahedral gold cores. The substantially red-shifted Au surface plasmon resonance (SPR) absorption band due to the Cu2O shell with a large refractive index remains fixed despite changes in the shell thickness. However, tuning the shell shape, and hence the surface facet, the Au SPR band can differ by as much as 26 nm. The Cu2O shells also display facet-dependent optical properties. Here in the first study, we examined if the same facet-dependent optical properties are observable in Pd‒Cu2O and Au nanorod‒Cu2O core‒shell nanocrystals. Nicely, the same facet-dependent optical properties are observed in these nanostructures. However, the Pd SPR band in Pd‒Cu2O cubes is more blue-shifted than Pd‒Cu2O truncated octahedra, whereas in the Au‒Cu2O case the Au SPR band of cubes is more red-shifted than octahedra. The short Au nanorod cores shift the SPR band directly to 1010‒1235 nm into the second biological window with the Cu2O shells. The small Au‒Cu2O core‒shell nanocrystals were tested for photothermal effect for the first time. Remarkably, giving enough near-IR irradiation energy, the ethanol solvent containing Au‒Cu2O nanoparticles can raise the temperature to 65 ºC after 300 sec from room temperature. This property can be exploited for converting sun light to thermal energy. Au nanoparticles can deform after long illumination time. By coating Cu2O shells outside Au cores, the stability and absorption cross section will increase and the LSPR property is tunable by changing the shell morphology and using short rods. These structures have potential as ultrasmall and highly efficient plasmonic heaters.