Synthesis and Properties of a Red Na[sub.5]Zn[sub.2]Gd[sub.1−x][sub.6]: xEu[sup.3+] Phosphor

Novel Eu[sup.3+]-doped Na[sub.5]Zn[sub.2]Gd(MoO[sub.4])[sub.6] triple molybdate phosphors were fabricated by the sol-gel method. The structure, morphology, and luminescent properties have been characterized by X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), FTIR spectroscopy, and luminescence spectroscopy. The results indicated that the synthesized Na[sub.5]Zn[sub.2]Gd[sub.1−x](MoO[sub.4])[sub.6]: xEu[sup.3+] phosphor consisted of a pure phase with monoclinic structure. Under excitation at 465 nm, the Na[sub.5]Zn[sub.2]Gd[sub.1−x](MoO[sub.4])[sub.6]: xEu[sup.3+] phosphor exhibits an intensive red emission band around 610 nm corresponding to the transition of [sup.5]D[sub.0]→[sup.7]F[sub.2] which is much higher than that [sup.5]D[sub.0]→[sup.7]F[sub.1] at 594 nm, which was appropriate for a blue LED. According to the influence of the synthesis conditions, the phosphors showed the highest emission intensity when the doping concentration of Eu[sup.3+] was 25 mol.% and the molar ratio of citric acid to metal ions was 2:1. Na[sub.5]Zn[sub.2]Gd[sub.0.75](MoO[sub.4])[sub.6]: 0.25 Eu[sup.3+] with the color coordinates (x = 0.658, y = 0.341) is a more stable red phosphor for blue-based white LEDs than the commercial Y[sub.2]O[sub.2]S: Eu[sup.3+] red phosphor (0.48, 0.50) due to its being closer to the NTSC standard values (0.670, 0.330).