Enhanced Directional Fluorescence Emission of Randomly Oriented Emitters via a Metal–Dielectric Hybrid Nanoantenna

This paper reports a hybrid nanoantenna consisting of an inner metal nanodisk and an outer dielectric ring cavity with superior fluorescence enhancement performance. Based on the multipole decomposition analysis and the coupled oscillator model, it is found that the surface plasmon resonance of the metal nanodisk could interact with the magnetic dipole mode of the dielectric ring more strongly than the electric dipole mode, improving the excitation rate in the gap region by more than 1 order of magnitude compared to those from the pure metal or dielectric constituent. The hybrid structure partially inherits the low loss advantage of the dielectric component, dramatically boosting the radiative decay rate and generating a decent quantum yield. The enhancement factor for a single emitter could reach more than one order of magnitude higher than those from the pure metal and dielectric counterparts, depending on the emitter’s location and orientation. The overall emission intensity of multiple randomly oriented emitters are estimated via the reciprocity principle, which can reach more than 1500 than that in free space and nearly 2 orders of magnitude higher than those from pure metal or dielectric counterparts. On top of that, an excellent directional radiation pattern is obtained in the hybrid configuration with a maximum directivity enhancement >3000, and 74% of total power propagates upwardly. This robust hybrid structure shows the possibility to leverage the advantages from both metal and dielectric, which could be useful in fluorescence sensing, nonlinear optics, and quantum photonics.