Metallic Nanoshells with Semiconductor Cores: Optical Characteristics Modified by Core Medium Properties

It is well-known that the geometry of a nanoshell controls the resonance frequencies of its plasmon modes; however, the properties of the core material also strongly influence its optical properties. Here we report the synthesis of Au nanoshells with semiconductor cores of cuprous oxide and examine their optical characteristics. This material system allows us to systematically examine the role of core material on nanoshell optical properties, comparing Cu2O core nanoshells (epsilon(c) similar to 7) to lower core dielectric constant SiO2 core nanoshells (epsilon(c) = 2) and higher dielectric constant mixed valency iron oxide nanoshells (epsilon(c) = 12). Increasing the core dielectric constant increases nanoparticle absorption efficiency, reduces plasmon line width, and modifies plasmon energies. Modifying the core medium provides an additional means of tailoring both the near- and far-field optical properties in this unique nanoparticle system.