Investigation of remote-phosphor white light-emitting diodes with improved scattered photon extraction structure

In this study, an improved scattered photon extraction (SPE) package structure with a reflection plate over the remote phosphor layer is presented. The important factors for the remote phosphor layer in the conventional and improved SPE package structures, including the phosphor layer thickness and phosphor concentration, are also studied. The simulation results show that the yellow-blue ratio (YBR) of the conventional and improved SPE package structure increases with the phosphor concentration when the phosphor layer is thin and that the YBR is saturated when the layer is thick. The experimental results show that for both conventional and improved SPE package structure, the correlated color temperature (CCT) decreases as the phosphor concentration increases. However, the YBR of the improved SPE package structure is higher than that of the conventional SPE package structure for a given phosphor layer thickness and phosphor concentration. That is, in the conventional SPE package structure, it is necessary to increase the phosphor concentration and then increase the absorption of blue light to obtain more yellow light. Hence, for the improved SPE package structure, less phosphor is required in the phosphor layer for achieving the chosen CCT.