Multi-sites induced ultra-broadband luminescence based on Eu2+ doped whitlockite-type phosphor for full-spectrum WLEDs

Ultra-broadband-emitting phosphors are crucial for achieving high-quality full-spectrum WLEDs. However, it is difficult to achieve ultra-broadband emission by doping a single luminescent center. In this work, we propose a strategy to achieve ultra-broadband orange-red emission through utilizing Eu2+ selective occupation in multi-cation sites whitlockite-type phosphate Sr8Mg2Na(PO4)7. The result indicates that Eu2+ can occupy Sr1Mg1, Sr2Mg2, and Sr3Mg3 sites, and generate an ultra-broadband emission ranging from 400 to 800 nm with dominant emission at 620 nm and a FWHM of 220 nm upon 385 nm excitation. Interestingly, a new emission shoulder at 430 nm is obtained, which is demonstrated to ascribed to Eu2+ occupying the Mg4Na1 site in a weak crystal field. As an ultra-broadband-emitting and red-light abundant phosphor, the full-spectrum WLEDs shows much higher color index than that of YAG: Ce3+. Moreover, an ultraviolet light pumped full-spectrum WLED with a high Ra (∼ 92) and low CCT (∼ 4275 K) is fabricated by mixing the Sr8Mg2Na(PO4)7: Eu2+ and commercial phosphors BAM: Eu2+, Mn2+. In summary, this work deeply investigated the luminescence properties of Eu2+ in whitlockite-type phosphor Sr8Mg2Na(PO4)7 and is expected to guide the design of novel broadband-emitting phosphors with multi cationic sites for emerging full-spectrum WLED applications.