Plasmon resonances in metallic nanoparticles augment the Förster resonance
energy transfer (FRET) between two molecules. We calculate and analyze comparatively
the enhancement factors of FRET for a metallic nanosphere and for a metallic spherical
nanoshell by finite element method (FEM). These calculations are compared with analytical
results obtained from the knowledge of spectral properties of the Neumann-Poincaré
(electrostatic) operator for sphere. With respect to the plain metallic nanosphere, the
spherical nanoshell shows a greater tunability of energy range for which the energy transfer
is enhanced. Our work can be relevant for using FRET for various applications regarding
porous materials. | 
