White Scattered Photon Extraction LEDs with Multi-Phosphor Layers

Early phosphor-converted white light-emitting diodes (LEDs) produced light with poor color characteristics in terms of color rendering index (CRI) and correlated color temperature (CCT). More recent LEDs have improved their color properties by combining multiple phosphors instead of using a single yellow phosphor such as YAG:Ce. Several manufacturers are now adding a red phosphor to the commonly used YAG:Ce to improve color properties. The common practice is to create a random mixture of multiple phosphors that is spread around the LED chip. In this study, the researchers questioned the impact of randomly mixing the phosphors versus stacking different phosphors in layers, as well as the effect of the order of the layers.