Structure evolution and tunable luminescence of (Sr_{0.98- m}Ba_mEu_0.02)₂Ca(Mo_{1- n}W_n)O₆ phosphor with ultraviolet excitation for white LEDs

Double perovskite (Sr_0.98-mBa_mEu _0.02)₂Ca(Mo_1-nW_n)O ₆ 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 (Sr _0.98-mBa_mEu_0.02) ₂CaMoO₆ phosphors. These series of phosphors could be effectively excited by near ultraviolet light and emitted a dominant 594 nm (⁵D₀-⁷F₁). The hypersensitive ⁵D₀-⁷F₂ transition (615 nm) 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 W ⁶⁺ 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(Mo_0.5W_0.5)O ₆:Eu phosphor had the highest luminescence intensity and quantum yield comparing to the commercial red phosphors.