Shaping the Fluorescent Emission by Lattice Resonances in Plasmonic Crystals of Nanoantennas

We demonstrate that the emission of light by fluorescent molecules in the proximity of periodic arrays of nanoantennas or plasmonic crystals can be strongly modified when the arrays are covered by a dielectric film. The coupling between localized surface plasmon resonances and photonic states leads to surface modes which increase the density of optical states and improve light extraction. Excited dye molecules preferentially decay radiatively into these modes, exhibiting an enhanced and directional emission.

Figure 1

(a) Measurements and (b) FDTD calculations of the transmittance through a 2D plasmonic crystal of gold nanoantennas on top of a glass substrate (black dotted lines) and through a similar plasmonic crystal covered by a 50 nm thick PVB layer (red solid lines). Inset in (b): Scanning electron microscope image of a plasmonic crystal.

Figure 2

Near field intensity enhancement in a 2D plasmonic crystal of nanoantennas on a glass substrate covered by a PVB layer. The field is calculated on the plane intersecting the nanoantennas at their middle height ($z=20\mathrm{nm}$). The calculations are at (a) $\lambda =695\mathrm{nm}$ and (b) $\lambda =905\mathrm{nm}$, which correspond to the LSPR and to the lattice surface mode, respectively.

Figure 3

(a) Transmittance of light polarized parallel to the short axis of the nanoantennas as a function of the normalized frequency $\omega /c$ and the wave number $k_{\parallel }$. The solid lines represent the Rayleigh anomalies. (b) Transmittance spectrum at $k_{\parallel }=5.47\times {10}^{-4}\mathrm{rad}{\mathrm{nm}}^{-1}$, i.e., the wave vector indicated by the dotted vertical line in (a). Thin black arrows indicate the Rayleigh condition and the LSPR, the thick red arrows indicate the lattice surface resonances.

Figure 4

(a) Fluorescence enhancement or the fluorescence of dye molecules in the proximity of a plasmonic crystal normalized by the fluorescence of dye molecules on an unpatterned substrate. (b) Transmittance as in Fig. 3a. (c) Fluorescence enhancement spectra at three different values of $k_{\parallel }$.

Figure 5

(a) Transmittance spectrum through a plasmonic crystal of nanoantennas for incident angle ${\theta }_{\mathrm{in}}=50°$ and polarization parallel to the long axis of nanoantennas. (b) FDTD calculation of the near field intensity enhancement around one nanoantenna at a wavelength of 685 nm and for an angle of incidence ${\theta }_{\mathrm{in}}=50°$.