Extraordinary fluorescence enhancement in metal-dielectric core-shell nanoparticles

Contrary to a paradigm of metal-enhanced fluorescence, unusually thick dielectric coatings can be very favorable to achieve extreme values of averaged fluorescence enhancement factor $\bar F\gtrsim 3000$ for emitters located on the surface, or in the interior, of the shell of Au@dielectric spherical core-shell particles under realistic conditions, even for the emitters with 100% intrinsic quantum yield. Thick dielectric coatings facilitate high-quality transverse electric (TE) multipole ($\ell=7$) resonances which are shown as the major cause for the reported extraordinary values of $\bar F$.