Eu³⁺ Site Distribution and Local Distortion of Photoluminescent Ca₃WO₆:(Eu³⁺, K⁺) Double Perovskites as High‐Color‐Purity Red Phosphors

Abstract

In this study, Eu3+ and K+ co‐doped Ca3WO6 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 Eu3+ fluorescence line‐narrowing (FLN) results, used to estimate the Eu3+ occupation at given sites (so‐called A and B sites) in the host crystal (A2BMO6; A, B = Ca; M = W), reveal that the Eu3+ ions have a twin distribution in both the A and B sites with high asymmetry ratios of ΛA = 9.7 and ΛB = 10.7, respectively. More interestingly, at lower Eu3+ doping levels, the ions are predominantly located at the B sites (≈75%), indicating that the high color purity of Ca3WO6:(Eu3+, K+) is mainly caused by the high asymmetry ratios of the Eu3+ sites. Rietveld refinement combined with the FLN technique provides more reliable results for increasing the Eu3+ substitution at the A site with Eu3+ and K+ doping concentrations, which lower the lattice energy of Ca3WO6:(Eu3+, 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)O12 A‐site cuboctahedra and Ca(Eu)O6 B‐site octahedra, partially accounting for the higher Λ values.

Preparation of a novel violet-excitable Na3YSi2O7:Eu2+ green phosphor via salt-flux assistance and its luminescence properties

“…S3b, ESI†) not only shows a dominant wide emission band of Eu 2+ , but also sharp characteristic emission peaks of Eu 3+ located at 594, 614, 650, and 704 nm, which belong to the 5 D 0 → 7 F 1 , 5 D 0 → 7 F 2 , 5 D 0 → 7 F 3 , 5 D 0 → 7 F 4 characteristic transitions of the Eu 3+ ion, respectively. 45–47 Perhaps due to the structural characteristics of the Na 3 YSi 2 O 7 matrix material, we optimized the synthesis process but still could not completely eliminate Eu 3+ . Similar phenomena to Eu 3+ residue were also observed in similar systems K 3 YSi 2 O 7 :Eu 2+ 28 and Rb 3 YSi 2 O 7 :Eu 2+ .…”

A brief review of characteristic luminescence properties of Eu3+ in mixed-anion compounds

“…, tungstates with W 6+ or molybdates with Mo 6+ ), a broad absorption band is observed in the near-UV region at 300–400 nm, which is not attributed to the Eu 3+ –O 2− CT transition, but to the CT transition between the d orbitals of d 0 cations and O 2p orbitals. 16,18,118,119 For the oxide hosts, which are very important as practical materials, the Eu 3+ –O 2− CT excitation bands are located in the deep-UV region below ∼300 nm. The red shift of the CT band is a challenge for applications employing popular near-UV or purple LEDs.…”

“…Eu 3+ -doped phosphors that can be excited by near-UV light have been explored and investigated to achieve efficient warm-white LEDs. 15–18 In addition, advanced functional luminescent materials, such as persistent phosphors and thermometers, have been designed through theoretical and (semi-)empirical models based on knowledge accumulated over the years. 19–25…”

Photoluminescence Study of Undoped and Eu-Doped Alkali-Niobate Aluminosilicate Glasses and Glass-Ceramics

“…Nevertheless, the study of the shortest components with the Xe lamp used here is challenging. To clarify the main mechanisms, further studies could use fluorescence line narrowing and site-selective fluorescence decay under different excitation lasers [46]. Figure 8.…”