Synthesis and Luminescence Properties of Orange-Red-Emitting M2Si5N8:Eu2+ (M = Ca, Sr, Ba) Light-Emitting Diode Conversion Phosphors by a Simple Nitridation of MSi2

Eu2+-doped M2Si5N8 (M = Ca, Sr, Ba) orange-red phosphors were successfully prepared by a simple, direct, and efficient solid-state reaction using air-stable MSi2, Eu2O3, and alpha-Si3N4 as the starting materials under N-2-H-2 (5%) atmosphere. The influence of the type of the alkaline-earth ion on the phase structure and luminescence properties has been investigated. The results show that the synthesized powders have a single-phase crystal structure of M2Si5N8 for M = Ca, Sr, and a little amount of BaSi7N10 impurity phase for M = Ba. Under the blue light excitation, M2Si5N8: Eu2+ shows a typical broad band emission of Eu2+ ranging from orange to red (585-620 nm) depending on the type of M ion. The emission intensity, conversion efficiency, and thermal stability increase with the sequence of CaoBaoSr, which suggests that Sr2Si5N8:Eu2+ has the highest application potential as a red conversion phosphor for white light-emitting diodes.