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Series of Eu 3+ substituted Na(Gd 1− x Eu x )MgWO 6 phosphors were successfully synthesized by a EDTA-citric acid complexing method. The crystal structure, doping site, morphology, and luminescent properties under different Eu 3+ concentrations were investigated by XRD, Rietveld refinement, Raman spectra, FTIR, SEM and fluorescence spectra as well as Judd–Ofelt analysis and quenching theory. The phosphors had monoclinic double perovskite structure with space group C2/m , rock-salt ordering of B-site (Mg/W) and layered ordering of A-site (Na/Gd/Eu). The redshift of Raman T 2g (1) mode proved Eu 3+ ions had uniformly substituted into A-site. The rare alternative excitation appeared in phosphors that the charge transfer band (CTB) altered from O–W into O–Eu and the strongest excitation altered from CTB into f – f transition of Eu 3+ . The quenching concentration for hypersensitive 5 D 0 – 7 F 2 transition of Eu 3+ reached up to 50.0 mol%, while both the intensity ratio of 5 D 0 – 7 F 2 / 5 D 0 – 7 F 1 and Judd–Ofelt parameter Ω 2 reached the maximum. These two channels of alternative excitation and delayed concentration quenching dually enhanced the luminescence of NaGdMgWO 6 :Eu 3+ phosphor. It is a potential red material for NUV and blue LED chips. [ABSTRACT FROM AUTHOR]

Abstract: Double perovskite (Sr0.98− m Ba m Eu0.02)2Ca(Mo1− n W n )O6 phosphors were successfully synthesized by an improved citrate–EDTA complexing method. The structure evolution and the resulting luminescence variation were systematically investigated by X-ray diffraction with Rietveld structure refinement, Fourier transform infrared spectra, Raman spectra, diffuse reflection spectra and photoluminescence spectra. The increased crystal symmetry and increased lattice parameters were observed from (Sr0.98− m Ba m Eu0.02)2CaMoO6 phosphors. These series of phosphors could be effectively excited by near ultraviolet light and emitted a dominant 594nm (5D0–7F1). The hypersensitive 5D0–7F2 transition (615nm) varied with the changed structure symmetry. The CIE chromaticity coordinates were tuned from (0.642, 0.348) to (0.601, 0.389). The luminescence intensity of W6+ substituted powders was greatly enhanced by the blue shift of charge transition band of (Mo/W)O6 with stable emission color. The composition-optimized Sr2Ca(Mo0.5W0.5)O6:Eu phosphor had the highest luminescence intensity and quantum yield comparing to the commercial red phosphors. [Copyright &y& Elsevier]