Novel double perovskite Na1-xEu1+x/3MgWO6 (0 ≤ x ≤ 0.4) phosphors for white LEDs: Sol-gel controlled synthesis, microstructure and luminescence properties

Abstract

Novel double perovskite Na1-xEu1+x/3MgWO6 phosphors are synthesized through sol-gel route, and the effects of x on the microstructures and luminescence properties of the obtained phosphors are systemically investigated. Under the determined sintering conditions, all of the Na1-xEu1+x/3MgWO6 (0 ≤ x ≤ 0.4) phosphors are pure monoclinic double perovskite structure, whereas there is an obvious impure phase in the sample Na1-xEu1+x/3MgWO6 with x = 0.5, suggesting that there is a phase transformation between x = 0.4 and x = 0.5. All of the as-synthesized Na1-xEu1+x/3MgWO6 phosphors exhibit a weak orange emission at 592 nm and a very strong red emission at 615 nm under the excitation of 395 nm near-ultraviolet and 464 nm blue light. Compared with NaEuMgWO6, all of the Na1-xEu1+x/3MgWO6 (0 < x ≤ 0.4) phosphors have stronger characteristic red and orange emissions of Eu3+, displaying an initially increasing and then decreasing trend with increasing x. Due to the creation of the A-site cation vacancy in the double perovskite structure, the luminescence properties of the Na1-xEu1+x/3MgWO6 (0 < x ≤ 0.4) phosphors, including the intensity of characteristic red emission, thermal stability, and color rendering index, can be noticeably heightened compared with the NaEuMgWO6 phosphor. Most importantly, the Na1-xEu1+x/3MgWO6 phosphor with x = 0.2 possesses excellent thermal stability (maintain 78.21% and 55.30% of its initial red emission intensity at 150 °C and 250 °C, respectively), higher color rendering index of 78.3%, and lower correlated color temperature of 4905 K, having great application potential in warm WLEDs.