  We demonstrate an enhanced emission of high quantum yield molecules coupled
to dielectric metasurfaces formed by periodic arrays of polycrystalline silicon
nanoparticles. Radiative coupling of the nanoparticles, mediated by in-plane
diffraction, leads to the formation of collective Mie scattering resonances or
Mie surface lattice resonances (M-SLRs), with remarkable narrow line widths.
These narrow line widths and the intrinsic electric and magnetic dipole moments
of the individual Si nanoparticles allow to resolve electric and magnetic
M-SLRs. Incidence angle- and polarization-dependent extinction measurements and
high-accuracy surface integral simulations show unambiguously that magnetic
M-SLRs arise from in- and out-of-plane magnetic dipoles, while electric M-SLRs
are due to in-plane electric dipoles. Pronounced changes in the emission
spectrum of the molecules are observed, with almost a 20-fold enhancement of
the emission in defined directions of molecules coupled to electric M-SLRs, and
a 5-fold enhancement of the emission of molecules coupled to magnetic M-SLRs.
These measurements demonstrate the potential of dielectric metasurfaces for
emission control and enhancement, and open new opportunities to induce
asymmetric scattering and emission using collective electric and magnetic
resonances.
