Research ArticleMATERIALS SCIENCE

Li substituent tuning of LED phosphors with enhanced efficiency, tunable photoluminescence, and improved thermal stability

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Science Advances  11 Jan 2019:
Vol. 5, no. 1, eaav0363
DOI: 10.1126/sciadv.aav0363
  • Fig. 1 Structural characterization of N□xASO, N□xASO:Eu, and N□ASO:yLi, Eu phosphors.

    (A) Dependence of unit cell volume (V) on the VNa concentration (x) of N□xASO and N□xASO:Eu (0 ≤ x ≤ 0.25) obtained from PXRD patterns. a.u., arbitrary units. (B) PXRD patterns of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15). All diffraction peaks match well with the standard patterns of nepheline NaAlSiO4 (PDF card no. 35-0424). (C) Dependence of unit cell volume (V) on the Li doping concentration (y) of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15).

  • Fig. 2 Morphology and composition of N□ASO:yLi, Eu (y = 0.10) phosphor.

    Optical microscope photographs of the N□ASO:yLi, Eu (y = 0.10) microcrystal particles (A) without and (B) with 365-nm UV excitation. (C) SEM images of N□ASO:yLi, Eu (y = 0.10) microcrystal particles and (D) an enlarged particle. (E to H) Element mapping images of Na, Al, Si, and O in the selected N□ASO:yLi, Eu (y = 0.10) particle. (I) 7Li solid-state NMR spectrum of N□ASO:yLi, Eu (y = 0.12). (J to L) TEM and HRTEM images of the selected area and the corresponding SAED of N□ASO:yLi, Eu (y = 0.10). The SAED image was detected in the zone axis [Embedded Image] orientation.

  • Fig. 3 PL properties of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15).

    (A and B) PLE and PL spectra of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15). Both PLE and PL spectral intensities are enhanced, and the intensity of the minor peak at ~450 nm is increased relative to that of the dominant peak at ~535 nm. (C and D) Normalized Eu L3-edge XANES spectra and dependence of IEu2+/IEu3+ on the Li+ doping concentration (y) of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15).

  • Fig. 4 Thermal quenching behavior of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) and performance of fabricated WLED devices.

    (A) Temperature-dependent normalized integrated PL intensities of the commercial phosphor YAG:Ce3+ and N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) under 365-nm excitation, showing an improvement after doping with Li. (B) Temperature-dependent PL spectra of N□ASO:yLi, Eu (y = 0, 0.15), indicating the improved thermal stability for N□ASO:yLi, Eu (y = 0.15). (C) CIE chromaticity diagram and digital photographs of N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) phosphors (λex = 365 nm) and the fabricated WLED devices, which show a color tuning from yellow to green with increasing the doping content of Li+. (D) Emission spectra of WLED devices fabricated with the commercial blue phosphor BAM:Eu2+, the yellow/green phosphors N□ASO:Eu/N□ASO:0.15Li, Eu, and the commercial red phosphor KSF:Mn4+ on a near-UV LED chip (λ = 365 nm) under a current of 120 mA.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaav0363/DC1

    Fig. S1. Rietveld refinement of N□xASO and N□xASO:Eu.

    Fig. S2. Rietveld refinement of N□ASO:yLi, Eu.

    Fig. S3. 27Al and 29Si NMR of N□ASO:yLi, Eu and N□xASO.

    Fig. S4. Thermal quenching behavior of YAG:Ce and N□ASO:yLi, Eu.

    Fig. S5. The CT transition energies of Eu3+ and the band gap calculation of the N□ASO:yLi host.

    Table S1. Main parameters of processing and refinement of the N□xASO (0 ≤ x ≤ 0.25) and N□xASO:Eu (0 ≤ x ≤ 0.25) samples.

    Table S2. Main parameters of processing and refinement of the N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) samples.

    Table S3. Fractional atomic coordinates and isotropic displacement parameters (Å2) of the N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) samples.

    Table S4. The photoelectric properties of WLEDs fabricated using yellow-emitting N□ASO:Eu phosphor, blue-emitting commercial BAM:Eu2+, and red-emitting commercial KSF:Mn4+ phosphor with a near-UV LED chip (λ = 365 nm) excitation under various drive currents.

    Table S5. Photoelectric properties of WLEDs fabricated using green-emitting N□ASO:0.15Li, Eu phosphor, blue-emitting commercial BAM:Eu2+, and red-emitting commercial KSF:Mn4+ phosphor with a near-UV LED chip (λ = 365 nm) excitation under various drive currents.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Rietveld refinement of N□xASO and N□xASO:Eu.
    • Fig. S2. Rietveld refinement of N□ASO:yLi, Eu.
    • Fig. S3. 27Al and 29Si NMR of N□ASO:yLi, Eu and N□xASO.
    • Fig. S4. Thermal quenching behavior of YAG:Ce and N□ASO:yLi, Eu.
    • Fig. S5. The CT transition energies of Eu3+ and the band gap calculation of the N□ASO:yLi host.
    • Table S1. Main parameters of processing and refinement of the N□xASO (0 ≤ x ≤ 0.25) and N□xASO:Eu (0 ≤ x ≤ 0.25) samples.
    • Table S2. Main parameters of processing and refinement of the N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) samples.
    • Table S3. Fractional atomic coordinates and isotropic displacement parameters (Å2) of the N□ASO:yLi, Eu (0 ≤ y ≤ 0.15) samples.
    • Table S4. The photoelectric properties of WLEDs fabricated using yellow-emitting N□ASO:Eu phosphor, blue-emitting commercial BAM:Eu2+, and red-emitting commercial KSF:Mn4+ phosphor with a near-UV LED chip (λ = 365 nm) excitation under various drive currents.
    • Table S5. Photoelectric properties of WLEDs fabricated using green-emitting N□ASO:0.15Li, Eu phosphor, blue-emitting commercial BAM:Eu2+, and red-emitting commercial KSF:Mn4+ phosphor with a near-UV LED chip (λ = 365 nm) excitation under various drive currents.

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