  Current effective medium theories for nano-shells are reviewed. A new method
for calculating the effective dielectric function of a core-shell nanoparticle
is presented and compared with existing theories showing clear advantages in
most conditions. It consists of introducing radiating effects in the polariz-
ability of the effective sphere, and considering the exact polarizability of
the core-shell constructed from the Mie scattering coefficient. This new
approach can be considered as an useful tool for designing coated particles
with desired plasmonic properties and engineering the effective permittivity of
composites with core-shell type inclusions which are used in photocatalysis and
solar energy harvesting applications.
