Single-phased, high-color-rendering index (CRI) white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes (WLEDs) and as an alternative to blends of tricolor phosphors. However, it is a challenge to create a high CRI white light from a single-doped activator. Here, we present a high CRI (Ra = 91) white-light phosphor, Sr5(PO4)3-x(BO3)xCl:Eu2+, composed of Sr5(PO4)3Cl as the beginning member and Sr5(BO3)3Cl as the end member. This work utilized the solid-solution method, and tunable Eu2+ emission was achieved. Color-tunable Eu2+ emissions in response to structural variation were observed in Sr5(PO4)3-x(BO3)xCl solid solutions. This was further confirmed using X-ray Rietveld refinement, electron paramagnetic resonance spectroscopy, and in the photoluminescence spectra. The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr5(PO4)3Cl:Eu2+ and an induced Eu2+ yellow emission at approximately 550 nm in the solid solution. Importantly, the white-light phosphors showed a greater R9 = 90.2 under excitation at 365 nm. This result has rarely been reported in the literature and is greater than that of (R9 = 14.3) commercial Y3Al5O12:Ce3+-based WLEDs. These findings demonstrate the great potential of Sr5(PO4)3-x(BO3)xCl:0.04Eu2+ as a white-light phosphor for near-UV phosphor-converted WLEDs. These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu2+-doped compound.

A series of single-phased (Sr3-x,Ca1-y-z,Ba)(PO4)3Cl (SCBPO_Cl):xEu(2+), yTb(3+), zMn(2+) phosphors were synthesized by high-temperature solid-state reaction, and luminescent properties of these phosphors were investigated by means of photoluminescence and microcathode luminescence (μ-CL). Under UV excitation, white-light emission was obtained from triactivated SCBPO_Cl phosphors via combining three emission bands centered at 450, 543, and 570 nm contributed by Eu(2+), Tb(3+), and Mn(2+), respectively. White-light emission with the three emission bands is further demonstrated in the fluorescence microscope images, CL spectrum, and μ-CL mappings, which strongly confirm that the luminescence distribution of as-prepared SCBPO_Cl:xEu(2+), yTb(3+), zMn(2+) phosphors is very homogeneous. Both spectral overlapping and lifetime decay analyses suggest that dual energy transfers, that is, Eu(2+)→Tb(3+) and Eu(2+)→Mn(2+), play key roles in obtaining the white emission. The International Commission on Illumination value of white emission as well as luminescence quantum yield (51.2-81.4%) can be tuned by precisely controlling the content of Eu(2+), Tb(3+), and Mn(2+). These results suggest that this single-phased SCBPO_Cl:xEu(2+), yTb(3+), zMn(2+) phosphor may have a potential application as a near-UV convertible white-light emission phosphor for phosphor-converted white light-emitting diode.

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We have synthesized and investigated a series of yellow-emitting Sr 3 Ce(PO 4 ) 3 :Eu 2+ phosphors, showing extremely broadband at around 535 nm (with FWHM of ca. 200 nm/6,760 cm -1 ) and large Stoke shift (ca. 8,265 cm -1 ), which is attributed to the 4f-5d transition of Eu 2+ without the contribution from Ce 3+ emission under excitation at long wavelength (> 370 nm). However, such broadband Eu 2+ emission is rather surprising, considering that there is only one cation site for Eu 2+ luminescence center. Herein, we investigate the crystal structure by performing X-ray Rietveld refinement on the synchrotron X-ray diffraction data, and demonstrate that both cation and anion sites in Sr 3 Ce(PO 4 ) 3 are disordered in the host lattice. These unusual structure characters generate a variety of distinct Eu 2+ sites, which is verified by the decay lifetime analysis and electron paramagnetic resonance spectra, and thus result in astonishing broadband yellow-emission. Moreover, a white LED device with color-rendering index of 86.5, color temperature of 5,996 K, and chromaticity coordinates of (0.32, 0.38), was obtained by combining a 405 nm near-UV LED chip and the phosphor blends of yellow-emitting Sr 3 Ce(PO 4 ) 3 :Eu 2+ and the commercial blue-emitting BaMgA 10 O 17 :Eu 2+ phosphor. These results indicate that the as-prepared yellow-emitting Sr 3 Ce(PO 4 ) 3 :Eu 2+ phosphor has potential applications in the dual-color-phosphor-converted WLEDs. Fig. 2 a) Experimental (cross), calculated (solid line) and difference (bottom) synchrotron power X-ray diffraction patterns for the sample SCPO:0.07Eu 2+ by the Rietveld refinement method. b) Crystal structure of the sample SCPO and c) the coordination of Sr/P with different oxygen atoms.Fig. 4 The normalized PL (λ ex =325 nm) and PLE (λ em =402 nm) spectrum of the host SCPO.Fig. 5 a) The PL spectra of the SCPO:xEu 2+ phosphors (0.01≤x≤0.2) under excitation at 375 nm. b) The dependence of the Stokes shift (∆S) and the λ em on Eu 2+ content.Fig. 6The normalized PLE spectra of the SCPO:xEu 2+ phosphors (0.01≤x≤0.2) by monitoring the lower energy emission. Besides, the PL spectrum of SCPO:0.07Eu 2+ under excitation at 365 nm is also shown in Fig. 6 as a reference.