Ca18.75Li10.5[Al39N55]:Eu2+Supertetrahedron Phosphor for Solid-State Lighting

Highly efficient red-emitting luminescent materials deliver the foundation for next-generation illumination-grade white light-emitting diodes (LEDs). Recent studies demonstrate that the hardly explored class of nitridoaluminates comprises intriguing phosphor materials, e.g., Sr­[LiAl3N4]:Eu2+ or Ca­[LiAl3N4]:Eu2+. Here, we describe the novel material Ca18.75Li10.5[Al39N55]:Eu2+ with highly efficient narrow-band red emission (λem ≈ 647 nm, full width at half-maximum, fwhm ≈ 1280 cm–1). This compound features a rather uncommon crystal structure, comprising sphalerite-like T5 supertetrahedra that are composed of tetrahedral AlN4 units that are interconnected by additional AlN4 moieties. The network charge is compensated by Ca2+ and Li+ ions located between the supertetrahedra. The crystal structure was solved and refined from single-crystal and powder X-ray diffraction data in the cubic space group Fd3̅m (No. 227) with a = 22.415(3) Å and Z = 8. To verify the presence of Li, transmission electron microscopy (TEM) investigations including electron energy-loss spectroscopy (EELS) were performed. Based on the intriguing luminescence properties, we proclaim high potential for application in high-power phosphor-converted white LEDs.