Broadband visible light absorption and plasmon emission through a self organized plasmonic crystal

Surface plasmon polariton (SPP) offers the opportunity to accelerate efficiently spontaneous emission of nanoemitters located close to a metallic surface, but as SPP modes are not coupled to far-field radiative modes, they induce loss of radiation. As metallic gratings radiate SPP modes in far field, they can be used to enhance the fluorescence of nanoemitters coupled to SPP. In this paper, a plasmonic crystal of centimetric size was fabricated by evaporating a thick layer of gold on an artificial silica opal used as a periodic template . By optical specular reflection spectra, a dip of almost complete absorption due to coupling to SPP was observed. The paper demonstrated a broad continuum of coupled wavelengths and perfect complete absorption over the visible spectrum whatever the direction of illumination is, illustrating a crystallographic arrangement at the microscopic scale and disorder at the macroscopic scale. The theoretical interpretation rely on a semi-analytical model based on the phase matching condition between wave vectors of propagating modes and SPP modes mediated by the metallic grating characteristic vectors. This opens new possibilities in fields where light-plasmon coupling is required over a broad range of wavelengths and incidence orientations. To study the fluorescence of nanoemitters coupled to the gold corrugated surface, an intermediate 80 nm silica layer was sputtered to avoid quenching. Colloidal CdSe/ZnS nanocrystals were then deposited on silica and performed angle and polarization-resolved emission spectra.