  We report the design of highly efficient optical antennas employing a
judicious synthesis of metallic and dielectric materials. In the proposed
scheme, a pair of metallic coupled nanoparticles permits large enhancements in
both excitation strength and radiative decay rates, while a high refractive
index dielectric microsphere is employed to efficiently collect light without
spoiling the emitter quantum efficiency. Our simulations indicate potential
fluorescence rate enhancements of 3 orders of magnitude over the entire optical
frequency range.
