Eu 3+ Site Distribution and Local Distortion of Photoluminescent Ca 3 WO 6 :(Eu 3+ , K + ) Double Perovskites as High-Color-Purity Red Phosphors.

In this study, Eu 3+ and K + co-doped Ca 3 WO 6 double perovskite, a high-color-purity red phosphor, is quantitatively investigated using synchrotron X-ray diffraction Rietveld refinement, energy dispersive X-ray spectroscopy, and high-resolution PL spectroscopy. The Eu 3+ fluorescence line-narrowing (FLN) results, used to estimate the Eu 3+ occupation at given sites (so-called A and B sites) in the host crystal (A 2 BMO 6 ; A, B = Ca; M = W), reveal that the Eu 3+ ions have a twin distribution in both the A and B sites with high asymmetry ratios of Λ A  = 9.7 and Λ B  = 10.7, respectively. More interestingly, at lower Eu 3+ doping levels, the ions are predominantly located at the B sites (≈75%), indicating that the high color purity of Ca 3 WO 6 :(Eu 3+ , K + ) is mainly caused by the high asymmetry ratios of the Eu 3+ sites. Rietveld refinement combined with the FLN technique provides more reliable results for increasing the Eu 3+ substitution at the A site with Eu 3+ and K + doping concentrations, which lower the lattice energy of Ca 3 WO 6 :(Eu 3+ , K + ). The structural distortions owing to K + co-doping in terms of the quadratic elongation and bond-angle variance exhibit good correlations with the Ca(Eu)O 12 A-site cuboctahedra and Ca(Eu)O 6 B-site octahedra, partially accounting for the higher Λ values.