A new type of phosphate-based phosphor Na3CsMg7(PO4)6:Eu2+/Mn2+with high quantum efficiency and high thermostability

The Eu2+ ion, with the 4f75d1 electronic configuration, is one of the most important activated ions due to its symmetry-allowed 4f → 5d electron transition. Herein, we successfully prepared a new type of blue phosphor, Na3CsMg7(PO4)6:xEu2+ (NCMP:xEu2+), in which Eu2+ occupies the Na+ sites of the host lattice. Under 395 nm light excitation, a broad emission band from 410 to 550 nm can be seen, peaking at 458 nm, due to the 5d → 4f transition of Eu2+. Moreover, Eu2+ can be used as a sensitizer ion in an NCMP host. For co-doping phosphor NCMP:0.18Eu2+/0.4Mn2+, both Eu2+ and Mn2+ emission bands can be seen using 395 nm as the excitation wavelength for the occurrence of Eu2+ → Mn2+ charge transfer. The optimized concentration of Eu2+ for NCMP:xEu2+ is x = 0.18, with high internal (IQE) and external quantum efficiencies (EQE) of 66.4% and 22.8%. The luminescence of NCMP:0.18Eu2+ has high thermostability with 77.3% the intensity at 450 K compared to that at 300 K. Finally, a white illuminating lamp was produced using a 395 nm UV chip, blue phosphor NCMP:xEu2+, green phosphor (Sr,Ba)2SiO4:Eu2+ and red phosphor CaAlSiN3:Eu2+ with CIE coordinates of (0.378, 0.369), color temperature (CCT) of 3971 K, and color rendering index (Ra) of 79.8.