Green-emitting Yb2+-doped α-SiAlON phosphors prepared by spark plasma sintering

Divalent ytterbium-doped Ca-α-SiAlON phosphors were synthesized by a spark plasma sintering (SPS) method without a reducing gas. A single phase Ca-α-SiAlON:Yb2+ was successfully achieved at relatively low temperature of 1600 °C. Its photoluminescence excitation spectrum showed a broad band peaking at 450 nm due to the 4f135d1 → 4f14 transition of Yb2+ ions, while a corresponding green emission band was observed at 545 nm. The post-annealing in a reduced atmosphere significantly improved the luminescent properties by increasing the crystallinity, reducing the carbon contamination, and changing the residual Yb3+ to Yb2+ in as-synthesized samples. The post-annealed powders, compared to commercial YAG:Ce3+ and silicate phosphors, showed a low thermal quenching due to the rigid crystal structure.

► Fabrication of Ca- and Yb-doped SiAlON phosphor by spark plasma sintering. ► Ca-α-SiAlON:Yb2+ phosphor exhibits a suitable green emission of 545 nm for white LEDs. ► Post-annealing increases the photoluminescence intensity effectively. ► SiAlON phosphor show superior thermal stability to the other counterparts.