Plasmonic LED device
Plasmonic nanostructures are known to influence the emission of near-by emitters. They can enhance the absorption and modify the external quantum efficiency of the coupled system. To evaluate the possibility of using plasmonics to enhance the light emission of a phosphor-converted LED device and create an efficient directional light source, regular arrays of aluminium nanoparticles covered with a red dye layer are investigated. In arrays of aluminum nanocylinders with a diameter of ca 140 nm combined with a thin (650 nm) layer of luminescent material, very narrow resonances have been observed, which lead to large enhancement factors of up to 70 and 20 for excitation with a directional blue laser source and a lambertian LED respectively, in a small spectral range for particular angles. The measured resonances agree very well with finite-difference time-domain numerical simulations. These changes in the angular emission profile of the red dye as well as the spectral shape of its emission can help to optimize the efficacy of phosphor-converted LED modules and increase the amount of useable light in a certain angular cone. Using Fourier microscopy, large modifications of the angular emission profile as well as spectral shaping are observed for these plasmonic LED devices if compared to reference samples without plasmonic nanostructures.