Efficient, stable, broadband cyan-emitting Ca-substituted Ba₉Lu₂Si₆O₂₄:Eu²⁺ with multisite luminescence for NUV-wLEDs

In order to develop an efficient and stable broadband cyan phosphor for full spectrum white lighting emitting diodes (wLEDs), novel Ba9Lu2Si6O24:Eu2+, xCa(2+) is designed and synthesized. Ca-substitution induces Eu2+ ions into Lu3+ crystallographic site, which achieve rare nonequivalent cation substitution of Eu2+. Effects of Ca-substitution on crystal structure of matrix and phosphor are investigated by X-ray photoelectron spectroscopy, X-ray powder diffraction, transmission electron microscopy, and density functional thoery (DFT). Ba9Lu2Si6O24:Eu2+, xCa(2+) can be effectively excited by with near-ultraviolet (NUV) and exhibit broadband cyan emission with full width at half maximum (FWHM) of 119.7 nm at x = 0.2, due to the multisite luminescence centers. For the sample x = 0.2, the internal quantum efficiency is 92.61%, and the luminous intensity at 423 K remains 89% of that measured at room temperature. The rigid structure of [SiO4]-[LuO6]-[SiO4] doped with Eu2+ ion makes Ca-substituted samples exhibit excellent luminescence efficiency and thermal stability. Our work develops a significant strategy based on multisite cation regulation to explore NUV-excited broadband cyan phosphors for full spectrum wLEDs.