The initial excitement about the use of plasmonic nanostructures for the development of nanophotonic devices operating in the optical regime was later partially eclipsed with the observation that losses could, in some cases, overtake actual radiative properties . In this scenario, dielectric nanoantennas have recently emerged as promising alternative candidates to plasmonic systems in the visible range . When excited above their bandgap energies, high-refractive-index dielectric nanostructures can highly concentrate electric and magnetic fields within subwavelength volumes, while presenting ultra-low absorption compared to metals . In particular, by locally enhancing the incident light intensity, dielectric nanoantennas are expected not only to produce negligible heating, but also boost nonlinear phenomena and surface-enhanced spectroscopies, since their efficiencies increase with the excitation density.
In this presentation, Si, Ge, and GaP nanoantennas will be introduced as promising nanosystems for surface-enhanced fluorescence and Raman spectroscopies, as well as for generating efficient second and third harmonic light on the nanoscale at visible wavelengths [2,4-7]. It will be shown that their associated temperature increase at resonance can be over one order of magnitude lower than that corresponding to metals. At the same time, fluorescence enhancement factors of over 3000 and harmonic conversion efficiencies of nearly 0.01% will be demonstrated for suitably engineered dielectric nanostructures. Finally, hybrid dielectric/metallic nanoantennas will also be analyzed, and, in all cases, comparison will be made with reference plasmonic nanosystems.
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