Influence of dielectric core, embedding medium and size on the optical properties of gold nanoshells

The amplitudes of the dipole and quadrupole modes for gold nanoshells have been investigated with various dielectric constants for the core and the embedding medium and with various size of the nanoshells by means of Mie theory. With the increase in the dielectric constant of the core, it is found that the strengths of dipole and quadrupole modes become weak. We also observe with the increasing dielectric constant of the embedding medium that the strength of the quadrupole mode is enhanced quickly, whereas that of dipole mode increases first and then decreases. We further find that the amplitude maximum of the dipole mode appears when the total radius of the nanoshell reaches to 50 nm even if the ratio of the inner and outer shell radii is fixed. We have ascribed the changes of the dipole and quadrupole modes to the competition among the variations of induced surface charges, conduction electrons and oscillation electrons.