Solid state lighting (SSL) has shown a great potential to lower the energy consumption of general lighting. Research efforts have been made to improve the internal quantum efficiency and the stability of light-emitting diodes (LEDs). Using the fluorescence of a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light has been found as an efficient way to design white light LEDs. As high efficient and stable phosphor based LEDs are invented, the necessity of developing other methods to improve the emission pattern for SSL has come in view. During the last years, possible advantages has been found by using arrays of metallic nano-particles, which we call plasmonic nano-structures, to modify the emission of phosphor based LEDs. A major problem in plasmonic SSL is the losses induced by the metallic nano-particles, which reduces the external quantum efficiency. In this thesis, a simulation model based on a fine element method (FEM) has been built to study the absorptions in the plasmonic phosphor. A figure of merit (FoM) describing the radio of absorption in the phosphor layer and total absorption is defined. Comparison of simulation and experiment indicates that the external quantum efficiency can be estimated by the product of the FoM and the internal quantum efficiency. Influence of the sample parameters and illumination method on the absorption is studied by simulation, as a guide for the optimization the plasmonic phosphor system in terms of excitation.Since little knowledge is available on plasmonic white light, the influence of plasmonic nano-structure on the emission color has also been studied with a green dye and the mixture of green and red dyes. Large enhancements based on plasmonic nano-structures has been measured on the emission of green dye molecules as well as the mixture of green and red dyes. Quasi-white light emission is obtained at small emission angles from the mixture with plasmonic nano-structures.
|Date of Award||31 Aug 2013|
|Supervisor||M. Kemerink (Supervisor 1), Marc A. Verschuuren (External coach) & G. Lozano (External coach)|