Probing Vertical and Horizontal Plasmonic Resonant States in the Photoluminescence of Gold Nanodisks

Localized surface plasmon resonance (LSPR) on gold nanoparticles and nanostructures shows its capability to modulate the spontaneous emission rate for photoluminescence. However, beyond the quasi-static limit with oblique incidence conditions, probing a retardation-based plasmonic resonant state excited by the horizontal incident wave-vector component has not been reported yet in the plasmon-mediated photoluminescence of gold nanostructures. In this paper, we investigated the photoluminescence of individual and coupled gold nanodisks with increasing size, and the peaks in the size-dependent photoluminescence spectra are shown to originate from the preferential excitation of vertical (LSPR) and horizontal (retardation-based) plasmonic resonant states. We have also proposed a three-step model to well describe the contribution of vertical and horizontal plasmonic resonant states in the photoluminescence of gold nanodisks. Our study makes a new contribution to the understanding of photoluminescence from gold nanostructures, and it paves the way toward the applications of plasmon-mediated luminescence and biological studies.