Tuning Gold Nanorod-Nanoparticle Hybrids into Plasmonic Fano Resonance for Dramatically Enhanced Light Emission and Transmission

Abstract

We investigate the optical response of a gold nanorod array coupled with a semicontinuous nanoparticle film. We find that, as the gold nanoparticle film is adjusted to the percolating regime, the nanorod-film hybrids are tuned into plasmonic Fano resonance, characterized by the coherent coupling of discrete plasmonic modes of the nanorod array with the continuum band of the percolating film. Consequently, optical transmission of the percolating film is substantially enhanced. Even more strikingly, electromagnetic fields around the nanorod array become much stronger, as reflected by 2 orders of magnitude enhancement in the avalanche multiphoton luminescence. These findings may prove instrumental in the design of various plasmonic nanodevices.KEYWORDS Plasmonic Fano resonance, plasmon hybrid, gold percolating film, gold nanorod array, enhanced transmission, enhanced photoluminescence E xtensive research efforts have been devoted recently to utilizing metal nanostructures to manipulate the propagation, intensity, and polarization of light, [1][2][3][4][5][6] leading to the emergence of nanophotonics as a major new direction in photonics. In this emerging field, one central physical entity is plasmon, characterizing the collective excitation of conduction electrons in metal nanostructures. Many intriguing phenomena discovered recently, such as the squeezing of light into subwavelength nanoholes, 7-9 and the detection of molecules trapped between nanogaps via surface-enhanced Raman scattering (SERS) with single molecule sensitivity, [10][11][12] are tied to the coupling of incident light with plasmon modes. Such studies not only broaden our fundamental understanding of photon interaction with nanoscale systems, but also may have far-reaching technological impacts.In exploration of various intriguing plasmonic phenomena at the nanoscale, a widely studied and distinctive research emphasis is the exploitation of the coupling and hybridization of different plasmon modes supported by various elegantly fabricated metal nanostructures. [13][14][15][16][17][18][19][20][21][22] Compelling examples include the plasmon coupling of a discrete mode to a continuum band, known as the "plasmonic Fano resonance". The Fano type absorption spectra were first reported in hole arrays in thin metal films and coaxial metallic arrays due to interferences of localized and delocalized plasmon modes.23-25 A more vivid picture of the plasmonic Fano model with three interaction regimes was convincingly demonstrated in metallic nanoparticle-film systems by tuning the film thickness. 26 Recently, multiple Fano resonances in a metallic ring/disk dimer and twinned Fano resonances in the Au-Ag heteronanorod dimer were also reported. 27 Most research focused on the asymmetric Fano line-shape in the absorption spectra, but enhanced emissions and Raman scattering induced by constructive interferences via the plasmonic Fano effect are seldom explored, which is of great importance for both passive and active plasmonic nanosystems.In this Letter, ...

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Control of Fano resonances and slow light using Bose-Einstein condensates in a nanocavity

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