Effects of phosphor distribution and step-index remote configuration on the performance of white light-emitting diodes

Phosphor-converted white light-emitting diodes (pc-WLEDs) are fabricated by combining CaSi₂O₂N₂:Eu²⁺ and Ca₂Si₅N₈:Eu²⁺ phosphors with a blue chip. Experimental results demonstrate that placing the red phosphor layer above the yellow one (Y down/R up) yields the highest luminous efficiency, making it the preferable phosphor distribution for pc-WLEDs rather than Y up/R down. This finding suggests that the extent of overlap between the emission spectrum of short-emission-wavelength phosphors and the excitation spectrum of long-emissionwavelength phosphors and their luminous efficacy of radiation should be taken into account simultaneously when studying the optical characteristics of pc-WLEDs. Compared to common pc-WLEDs with silicone gel as the remote layer, the proposed step-index remote configuration exhibits superior luminous efficiency because of reduced total internal reflection and Fresnel loss.