Plasmon-Modulated Photoluminescence of Single Gold Nanobeams

In this work, we investigate the modulation of the photoluminescence (PL) of a single Au nanobeam (NB) by the surface plasmons of a Ag nanowire (NW) and the gap plasmons between the two nanostructures. By changing the polarization of the laser that excites the nanostructure and controlling the separation distance d between the two nanostructures, we found that the transverse surface plasmon resonance of the Ag NW enhanced the PL (at 520 nm) of the Au NB with a maximum effect at d = 7 nm. The PL enhancement (at 520 nm) was quenched and a new PL peak was observed at a longer wavelength for d < 7 nm. The PL quenching effect could be understood by the quadrupole-like plasmonic resonance between the Ag NW and the Au NB and be qualitatively explained by the mode dispersion as a function of d obtained using the transfer matrix transmittance calculation. FDTD simulations show that the new PL peak at a longer wavelength is caused by the waveguide-mode gap plasmons between the Au NB and the Ag NW.