Eu3+-activated Ca2YTaO6 double-perovskite compound: A novel highly efficient red-emitting phosphor for near-UV-excited warm w-LEDs

In this work, novel Eu 3+ ions activated red emitting Ca 2 YTaO 6 (CYT) phosphors have been prepared via a high-temperature solid-state reaction approach. Their crystal structure and photoluminescence properties were investigated by X-ray diffraction (XRD) patterns, photoluminescence excitation and emission spectra , and decay lifetimes. XRD Rietveld refinement results revealed that the CYT:Eu 3+ phosphors crystallized in the monoclinic structure with the space group of P 2 1 / n and lattice parameters of a  = 5.5989 Å, b  = 5.8449 Å, c  = 8.1016 Å, α  =  γ  = 90°, β  = 89.8799°, and V  = 264.625 Å 3 . The CYT: x Eu 3+ phosphors could be excited by near-ultraviolet light around 396 nm, and they showed bright narrowband red emissions peaking at 590, 614, 656, and 703 nm due to the 5 D 0 → 7 F J (J = 1–4) transitions of Eu 3+ ions. The 614 nm red emission corresponding to the 5 D 0 → 7 F 2 transition was dominant in the emission spectra, indicating that the Eu 3+ ions occupied non-centrosymmetric sites. The critical quenching concentration in CYT: x Eu 3+ phosphors was 50 mol%, and the optimal CYT:0.5Eu 3+ phosphors showed PL intensity as great as 4.2 times higher than the commercial red phosphors Y 2 O 3 :Eu 3+ . CIE chromaticity coordinates of CYT:0.5Eu 3+ phosphors were (0.6678, 0.3319), and the color purity reached up to 97.4%. The nonradiative energy transfer between the Eu 3+ ions in the CYT host was attributable to dipole-dipole interaction, and the critical distance was roughly 7.97 Å. A warm white light-emitting diode (w-LED) based on the combination of a 395 nm LED chip with a blend of commercial BaMgAl 10 O 17 :Eu 2+ blue phosphors and commercial (Ba,Sr) 2 SiO 4 :Eu 2+ green phosphors and as-prepared CYT:0.5Eu 3+ red phosphors was fabricated, which gave warm white-light emission with excellent CIE color coordinates of (0.3833, 0.3859), low correlated color temperature of 3991 K, high color rendering index of 92.1, and good luminous efficacy of 21.76 lm/W.