Directional outcoupling of photoluminescence from Eu(III)-complex thin films by plasmonic array

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