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.