A new type of phosphate-based phosphor Na 3 CsMg 7 (PO 4 ) 6 :Eu 2+ /Mn 2+ with high quantum efficiency and high thermostability.

The Eu ²⁺ ion, with the 4f ⁷ 5d ¹ 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, Na ₃ CsMg ₇ (PO ₄ ) ₆ : x Eu ²⁺ (NCMP: x Eu ²⁺ ), in which Eu ²⁺ 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 Eu ²⁺ . Moreover, Eu ²⁺ can be used as a sensitizer ion in an NCMP host. For co-doping phosphor NCMP:0.18Eu ²⁺ /0.4Mn ²⁺ , both Eu ²⁺ and Mn ²⁺ emission bands can be seen using 395 nm as the excitation wavelength for the occurrence of Eu ²⁺ → Mn ²⁺ charge transfer. The optimized concentration of Eu ²⁺ for NCMP: x Eu ²⁺ is x = 0.18, with high internal (IQE) and external quantum efficiencies (EQE) of 66.4% and 22.8%. The luminescence of NCMP:0.18Eu ²⁺ 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: x Eu ²⁺ , green phosphor (Sr,Ba) ₂ SiO ₄ :Eu ²⁺ and red phosphor CaAlSiN ₃ :Eu ²⁺ with CIE coordinates of (0.378, 0.369), color temperature (CCT) of 3971 K, and color rendering index ( R _a ) of 79.8.