Influence of high-refractive-index oxide coating on optical properties of metal nanoparticles

The localized surface-plasmon resonance absorption of metal nanoparticles is currently utilized in many fields such as near-infrared (NIR) curing and biomedical applications. In this paper, we study theoretically the influence of an oxide (SiO2, ZrO2, or TiO2) shell on a metal (Ag, Au, or Cu) nanoparticle from the point of view of shifting the resonance peak to a more desirable color or NIR wavelengths while conserving the intensity of the absorption or extinction peak. The computational models used in the studies include the Mie theory and the four-flux method. We find shifts of up to hundreds or even close to 1000 nm. Among the material combinations studied, the largest shifts are obtained with Ag-TiO2 core-shell nanoparticles when going from a few nanometers sized core without an oxide shell to a 100 nm size core with a 100 nm thick shell. However, the huge shifts happen together with severe intensity loss of the absorption peak, leading to a more conservative estimate of practically useful shifts of a few hundreds of nanometers. (c) 2013 Optical Society of America