A promising orange-yellow-emitting phosphor for high power warm-light white LEDs: Pure-phase synthesis and photoluminescence properties

Abstract

The high correlated colour temperature (CCT) and deficient thermal stability of widely-used YAG:Ce and InGaN white light systems prompt an urgent need for more outstanding succedaneum phosphors, among which Ce-doped La3Si6N11 (LSN:Ce) phosphor has the best performance in the yellow-orange area. However, it still has not gained popularity due to its low quantum efficiency and luminance quality, caused by many factors such as irregular particle morphology and impure chemical composition, especially the difficulty of obtaining a single phase without LaSi3N5 impurity. By doping with different alkaline-earth metal elements and adjustment of the lanthanum/silicon ratio in the raw materials, LSN:Ce and MLSN:Ce (M = Ca, Ba and Sr) phosphors with high purity were synthesised in this work. Compared to Ca and Sr, doping with Ba produced a better result, not only in the crystallisation of the LSN phase, but also in the red shift of the phosphor emission. To further improve the purity of LSN phosphors, the Si/La molar ratio was increased from 2:1 to 1:1.5, and finally resulting in a single phase when the ratio reached 1:1. The white LEDs fabricated with the LSN:Ce & BaLSN:Ce phosphors and InGaN blue light chips had lower CCTs at 3900 K and 3300 K, indicating the great potential of the phosphor for application in high power and display lighting.