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 (lambda(em) approximate to 647 nm, full width at half-maximum, fwhm approximate to 1280 cm(-1)). This compound features a rather uncommon crystal structure, comprising sphalerite-like T-5 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 Fd (3) over barm (No. 227) with a = 22.415(3) angstrom 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.