A novel composite structure to balance luminous efficacy and color rendering in laser-driven solid-state lighting

(Y,Ce) 3 Al 5 O 12 (YAG:Ce) ceramic is considered to be a suitable phosphor converter with a high quantum efficiency and excellent thermal stability for laser-driven lighting. However, the lack of red emission in the spectrum of YAG:Ce leads to the poor color quality of white light under excitation of laser diodes (LDs). Although current solutions were investigated to improve the color rendering index (CRI), they inevitably cause the decreased luminous efficacies (LE). How to balance the two luminous properties is still troubling researchers. In this study, a novel composite structure with large YAG:Ce grains surrounded by fine YAG:Cr grains was obtained by the two-stage hot-pressing process. The energy transfer between Ce 3+ and Cr 3+ was reduced because they were in different phases due to the structural design, thus improving the red emission while avoiding a sharp decline in the yellow emission. Moreover, there was no reaction and difference in thermal expansion coefficient between two phases due to the same matrix of YAG. Furthermore, the reflection loss in YAG:Cr‒YAG:Ce composite ceramic was reduced compared to layered-structure ceramics. Therefore, the maximal CRI reached 71.3 and the maximal LE was 255.8 lm/W, indicating an excellent application prospect in laser-driven lighting.