Highly symmetric lattice environment induced orange-red emitting of Eu in a novel tungstate phosphor with broad-band ultraviolet excitation.

In this work, we reported the synthesis and characteristic luminescence of an orange-red emitting phosphor NaBaYWO: Eu for ultra-violet white light emitting diodes. The phase compound, crystalline structure and morphology are analyzed. The results indicate that a heavy doping of Eu (x = 50%) is realized in NaBaYWO: xEu without any impurity phase. Moreover, the optical band gap is analyzed by diffuse reflectance spectroscopy and further confirmed by density function theory (DFT). Meanwhile, the as-synthesized NaBaYWO: Eu phosphor can be efficiently pumped by strong broad-band excitation around 315 nm due to the charge transfer transition from [WO] groups to Eu. Owing to the highly symmetric lattice environment of Eu in YO sites, a strong orange-red emission at 596 nm with color purity of 95.34% is obtained, corresponding to the D→F magnetic dipole transition of Eu ions. The critical concentration is obtained to be x = 15%, and the quenching mechanism is discussed to be dipole-dipole interaction. Furthermore, the temperature dependent emission behavior are analyzed, and the thermal quenching mechanism are explained by the variable temperature decay curve and configuration coordination diagram. Finally, an orange-red light emitting diode lamp is fabricated based on NaBaYWO: 15%Eu phosphor and 315 nm semiconductor chip. In summary, the results indicate that NaBaYWO: Eu phosphor has the potential to be an orange-red phosphor for white light emitting diodes.