Fangyi Weng

Northeast Institute of Geography and Agroecology, Beijing, Beijing Shi, China

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Publications (11)20.94 Total impact

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    ABSTRACT: The time-resolved luminescence spectra of the Eu <sup>3+</sup> doped SiO <sub>2</sub>– Al <sub>2</sub> O <sub>3</sub>– NaF – YF <sub>3</sub>– EuF <sub>3</sub> precursor glass reveal that Eu <sup>3+</sup> ions locate in both the oxygen-coordination environment and the fluorine-coordination one. After crystallization induced by heat treatment, the orthorhombic YF <sub>3</sub> nanocrystals with mean size of 22 nm embedded homogeneously in the glassy matrix. The Stark splitting emission, the low electric dipole <sup>5</sup> D <sub>0</sub>→<sup>7</sup> F <sub>2</sub> transition, the disappearance of the O <sup>2-</sup>– Eu <sup>3+</sup> charge transfer band and the reduction in Ω<sub>2</sub> value indicate the partition of Eu <sup>3+</sup> into the YF <sub>3</sub> lattice. Moreover, the nearly single-exponential luminescence decay curves of the Eu <sup>3+</sup>:<sup>5</sup> D <sub>0</sub> and <sup>5</sup> D <sub>1</sub> levels for the 0.1% Eu <sup>3+</sup> doped glass ceramic evidence that Eu <sup>3+</sup> ions mainly occupy the Y <sup>3+</sup> sites.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: Transparent SiO2–Al2O3–BaCO3–YF3–BaF2 glass ceramics co-doped with Yb3+/Ho3+ ions were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy observation revealed that BaYF5 nanocrystals incorporated with Yb3+ and Ho3+ were precipitated homogeneously among the oxide glass matrix. Three upconversion emission bands centered at 483 nm, 545 nm and 645 nm, corresponding to the 5F3 → 5I8, 5S2, 5F4 → 5I8 and 5F5 → 5I8 transitions of Ho3+ respectively, were detected under 976 nm excitation, ascribing to the efficient energy transfer from Yb3+ to Ho3+. The red emission is prevailing in the precursor glass, while the green one turns to be dominant in the glass ceramic.
    Materials Research Bulletin. 01/2010; 45(8):1017-1020.
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    ABSTRACT: Eu(3+)-doped transparent glass ceramics containing In(2)O(3) nano-crystals were prepared by melt quenching and subsequent heating. X-ray diffraction analysis, transmission electron microscope observation, and photoluminescence excitation spectra demonstrated that In(2)O(3) nano-particles sized 3-6 nm homogenously distributed among the glass matrix. Under excitation of these nano-particles, Eu(3+) luminescence was found greatly enhanced due to the energy transfer from the oxygen-vacancy-related defects of In(2)O(3) to Eu(3+) ions. The Eu(3+) content dependent energy transfer efficiency was evaluated, and the value reached 67% for 1 mol% Eu(3+) doped glass ceramics. Low temperature emission spectra demonstrated that the Eu(3+) ions of the glass ceramic locate mainly in the glass matrix.
    Physical Chemistry Chemical Physics 10/2009; 11(39):8774-8. · 4.20 Impact Factor
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    ABSTRACT: Rare earth (RE) ion doped glass ceramics containing hexagonal CeF(3) nanocrystals with a mean size of 12 nm were fabricated. Using Eu(3+) as the structural probe, Stark splitting emissions and the low forced electric dipole D5(0)-->F7(2) transition of Eu(3+) revealed the partition of RE ions into low-phonon-energy CeF(3) nanocrystals. Efficient energy transfers from Ce(3+) to Tb(3+) or Dy(3+) were found, and the energy transfer efficiency was evaluated. Under ultraviolet excitation, intense white-light emission was observed in Dy(3+)-doped samples owing to Dy(3+) resided in CeF(3) crystalline environment, indicating their potential application in white-light-emitting diodes.
    Optics Letters 10/2009; 34(19):2882-4. · 3.39 Impact Factor
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    ABSTRACT: The Eu3+ and Tb3+ doped glass ceramics containing tetragonal LiYbF4 nanocrystals were prepared. The Stark splitting emission, the low electric dipole 5D0→7F2 transition, and the long lifetime of Eu3+ evidenced the partition of rare earth into LiYbF4. For Tb3+ doped glass ceramic, intense ultraviolet emission of Tb3+: 5G6, 5D3→7F6 transition via cooperative sensitization of Yb3+ and bright blue cooperative luminescence originated from the coupled state of Yb3+–Yb3+ ionic pairs were achieved under 976 nm excitation, ascribing to the low-phonon-energy environment of rare earth ions enriched in nanocrystals and the efficient Yb3+–Tb3+ or Yb3+–Yb3+ interionic interactions.
    Applied Physics Letters 01/2009; 94(4):041909-041909-3. · 3.52 Impact Factor
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    ABSTRACT: Quantum cutting downconversion (DC) involving the emission of two near-infrared (NIR) photons for each ultraviolet (UV) photon absorbed is realized in the Ce <sup>3+</sup>/ Yb <sup>3+</sup> codoped borated glasses. Upon excitation of Ce <sup>3+</sup> ion with an UV photon at 330 nm, Yb <sup>3+</sup> ions emit two NIR photons at 976 nm through an efficient excitation of Ce <sup>3+</sup>:5d and subsequent cooperative energy transfer (ET) from Ce <sup>3+</sup>:5d to Yb <sup>3+</sup>:<sup>2</sup>F<sub>5/2</sub> . The maximum ET efficiency and the corresponding DC quantum efficiency were estimated to be 74% and 174%, respectively.
    Journal of Applied Physics 01/2009; · 2.21 Impact Factor
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    ABSTRACT: Yb3+-doped oxyfluoride glass ceramics were fabricated by melt-quenching and subsequent heating. X-ray diffraction and high-resolution transmission electron microscopy analyses evidenced that orthorhombic TbF3 nanocrystals with a mean size of 22 nm were homogeneously precipitated among the aluminosilicate glass matrix. The incorporation of Yb3+ ions into TbF3 crystals was confirmed by energy-dispersive X-ray spectroscopy. Under 976 nm near-infrared laser excitation, the glass ceramics exhibited intense green Tb3+:5D4 → 7FJ (J = 3, 4, 5, 6) up-conversion luminescence due to the cooperative energy transfer from two Yb3+ ions to one Tb3+ ion. In comparison, under 485 nm excitation, they yielded near-infrared quantum cutting down-conversion emission corresponding to Yb3+:2F5/2 → 2F7/2 transition, ascribing to the cooperative energy transfer from one Tb3+ ion to two Yb3+ ions. The energy transfer processes between Tb3+ and Yb3+ ions were discussed, and the energy transfer efficiency was evaluated.
    Journal of Physical Chemistry C - J PHYS CHEM C. 01/2009; 113(16):6406-6410.
  • ChemInform 01/2009; 40(5).
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    ABSTRACT: Transparent glass ceramics containing YF3 nano-crystals were fabricated by heat treatment of the SiO2–Al2O3–NaF–YF3–LnF3 (Ln=Er, Yb) glasses. X-ray diffraction and transmission electron microscopy analyses evidenced the homogeneous distribution of spherical YF3 nano-crystals sized 25–30nm among the glassy matrix. Energy dispersive X-ray spectroscopy measurement, combined with the Stark splitting of the absorption and emission bands, verified the incorporation of Er3+ and Yb3+ ions into YF3 nano-crystals. The infrared to visible up-conversion emission of Er3+ intensified with the increasing of Yb3+ concentration, ascribing to the increase of the efficiency of non-radiative energy transfer from Yb3+ to Er3+ which exceeded 45% for the 0.5Er3+/1.0Yb3+ co-doped sample. The up-conversion luminescence at 545 and 660nm were affirmed coming from two-photon excitation process.
    Ceramics International - CERAM INT. 01/2009; 35(7):2619-2623.
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    ABSTRACT: Quantum cutting downconversion involving the emission of two near-infrared photons for each blue photon absorbed is realized in transparent glass ceramics with embedded Pr3+/Yb3+: beta-YF3 nanocrystals. On excitation of Pr3+ ions with a visible photon at 482 nm, Yb3+ ions emit two near-infrared photons at 976 nm through an efficient cooperative energy transfer from Pr3+ to Yb3+, with optimal quantum efficiency close to 200%. The development of the near-infrared quantum cutting transparent glass ceramic could open a route to enhance the energy efficiency of the silicon solar cell by converting one blue solar photon to two near-infrared ones.
    Optics Letters 09/2008; 33(16):1884-6. · 3.39 Impact Factor
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    ABSTRACT: Transparent SiO2–Al2O3–NaF–YF3 bulk nano-composites triply doped with Ho3+, Tm3+ and Yb3+ were fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy measurements demonstrated the homogeneous precipitation of the β-YF3 crystals with mean size of 20nm among the glass matrix, and rare earth ions were found to partition into these nano-crystals. Under single 976nm laser excitation, intense red, green and blue upconversion emissions were simultaneously observed owing to the successive energy transfer from Yb3+ to Ho3+ or Tm3+. Various colors of luminescence, including bright perfect white light, can be easily tuned by adjusting the concentrations of the rare earth ions in the material. The overall energy efficiency of the white-light upconversion was estimated to be about 0.2%.
    Journal of Solid State Chemistry 01/2008; 181(10):2763-2767. · 2.04 Impact Factor