Abstract
A plasmonic array, consisting of metallic nanocylinders periodically arranged with a pitch comparable to the optical wavelength, is a system in which both the localized surface plasmon polaritons (SPPs) and diffraction in the plane of the array are simultaneously excitable. When combined with a phosphor film, the array acts as a photoluminescence (PL) director and enhancer. Since the array can modify both excitation and emission processes, the overall modification mechanism is generally complex and difficult to understand. Here, we examined the mechanism by simplifying the discussion using an emitter with a high quantum yield, large Stokes shift, and long PL lifetime. Directional PL enhancement as large as five-fold occurred, which is mainly caused by outcoupling, i.e., the PL trapped in the emitter film by total internal reflection is extracted into free space through the SPPs and diffraction. The present scheme is robust and applicable to arbitrary emitters, and it is useful for designing compact and efficient directional illumination devices.
Highlights
Metallic nanoparticles possess a very large polarizability, which causes strong light–matter interactions. This is due to surface plasmon polaritons (SPPs), i.e., coherent electronic oscillations in metallic nanoparticles driven by an external electromagnetic field.[1]
If an optical emitter is located in the proximity of a metallic nanoparticle, the radiative and nonradiative decay rates of the emitter are influenced by the presence of the nanoparticle.[2,3,4,5,6]
We focus on periodic arrays of metallic nanoparticles with a pitch comparable to the wavelength of light
Summary
Metallic nanoparticles possess a very large polarizability, which causes strong light–matter interactions. We focus on periodic arrays of metallic nanoparticles with a pitch comparable to the wavelength of light In these arrays, strong diffraction in the plane of the array, i.e., the Rayleigh anomaly, mediates the radiative coupling between neighboring SPPs to induce collective plasmonic modes.[20,21,22,23,24] Collective plasmonic modes can couple to the emission to enhance its intensity and control its directionality. We designed the Al nanocylinder array to sustain the collective modes at the wavelengths of the Eu3+ emission lines In this manner, we intentionally exclude the effect of pump enhancement (|E(λex)|2/|E0(λex)|2) and focus on the separation of the two remaining factors at λem, i.e., η/η0 and Cext/Cext[0]. The results suggest that outcoupling (Cext/Cext0) is the main factor of the enhancement in the present system
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