Size dependent optical properties of ZnO@Ag core/shell nanostructures

In this paper, we studied the effect of size and thickness variation on the optical properties of a system that consists of spherical ZnO@Ag core/shell composite nanostructures embedded in a dielectric host matrix. The effective dielectric function, polarizability, refractive index, and absorbance of the composite nanostructures are determined using the Maxwell-Garnett effective medium theory within the framework of the electrostatic approximation. The numerical simulations using nanoinclusions of radii 20 nm show interesting behavior in the optical responses of the ensemble. In particular, it is shown that for different values of metal fraction and filling factor, the polarizability, refractive index, and optical absorbance of the ensemble exhibit two sets of resonance peaks in the UV (around 300 nm) and visible (between 400 and 640 nm) spectral regions. These peaks are attributed to the surface plasmon resonance of silver at the ZnO/Ag and Ag/host-matrix interface. Moreover, when the Ag shell thickness is increased, the observed resonance peaks are enhanced; accompanied with slight red shifts in the UV and blue shifts in the visible regions. The results obtained may be used in various applications such as sensors and nano-optoelectronics devices in optimizing material parameters to the 'desired' values.