Limin Fu

Renmin University of China, Peping, Beijing, China

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Publications (9)39.49 Total impact

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    ABSTRACT: The bridging ligands in d–f bimetallic complexes play an important role in the excitation energy transfer (EET) process. To elaborate on the effect of the ligand on the EET process, a series of bridging ligands (μ-L), 1-(1′,10′-phenanthrolin-2′-yl)-4,4,4-trifluorobutane-1,3-dione (phen3f), 1-(1′,10′-phenanthrolin-2′-yl)-4,4,5,5,5-pentafluoropentane-1,3-dione (phen5f), 1-(2,2′-bipyridine-6-yl)-4,4,4-trifluorobutane-1,3-dione (bpy3f), and 1-(2,2′-bipyridine-6-yl)-4,4,5,5,5-pentafluoropentane-1,3-dione (bpy5f), and their corresponding iridium complexes, [(dfppy)2Ir(μ-L)] (dfppy=2-(4′,6′-difluorophenyl)pyridinato-N,C2′), as well as their corresponding heteroleptic IrIII–EuIII complexes [{(dfppy)2Ir(μ-L)}3EuCl]Cl2 were synthesized and characterized. Photophysical and kinetic results revealed that the alternation of the bridge ligand resulted in a systemic difference in the lowest triplet-state energy (T1) of the iridium complexes, the EET efficiency from iridium complexes to the EuIII ion, and a significant difference in the total luminescence quantum yields. Based on the nanosecond time-resolved phosphorescence spectra, a model for the energy-transfer mechanism was proposed for d–f bimetallic complexes, which indicated that the nonradiative relaxation of the excited energy of EuIII, especially energy dissipation by means of the T1 state, was the main reason for the discrepancy in the quantum yields of the four IrIII–EuIII complexes.
    ChemPlusChem 08/2013; 78(8).
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    ABSTRACT: Hierarchical TiO(2) microspheres assembled by nanospindles were prepared via a two-step hydrothermal method. The as-prepared products have uniform diameters of ∼450 nm and surface area of ∼88 m(2) g(-1). The optical investigation evidenced that the photoanode film has a prominent light scattering effect at a wavelength range of 600-800 nm and possesses enhanced dye loading capacity. In addition, the electron recombination and transport dynamic measurements indicated that these hierarchical products could suppress the recombination and improve the diffusion coefficient of the photoelectrons, which can be attributed to the improvement of the connectivity by bridging the neighbouring microspheres through the embedded nanospindles. As a result, a high power conversion efficiency of 8.5% was demonstrated, indicating a ∼30% improvement compared with the cell derived from the well-defined nanocrystalline microspheres (6.5%).
    Nanoscale 11/2012; · 6.73 Impact Factor
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    ABSTRACT: Zn-doped anatase TiO(2) nanoparticles are synthesized by a one-step hydrothermal method. Detailed electrochemical measurements are undertaken to investigate the origin of the effect of Zn doping on the performance of dye-sensitized solar cells (DSSCs). It is found that incorporation of Zn(2+) into an anatase lattice elevates the edge of the conduction band (CB) of the photoanodes and the Fermi level is shifted toward the CB edge, which contributes to the improvement in open-circuit voltage (V(OC) ). Charge-density plots across the cell voltage further confirm the increase in the CB edge in DSSCs directly. Photocurrent and transient photovoltage measurements are employed to study transport and recombination dynamics. The electron recombination is accelerated at higher voltages close to the CB edge, thus leading to a negative effect on the V(OC) .
    ChemPhysChem 08/2012; · 3.35 Impact Factor
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    ABSTRACT: We report a new complex Eu(tta)(3).bpt (tta = thenoyltrifluoroacetonate; bpt = 2-(N,N-di-ethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine) with excellent long-wavelength sensitized luminescent properties, in which four hydrogen atoms replace the methyl groups at the 3,3'- and 5,5'-positions of the pyrazolyl rings in a previously reported complex Eu(tta)(3).dpbt. Upon visible-light excitation (lambda(ex) = 410 nm) at 295 K, the quantum yield (Phi(Ln)(L)) of Eu(3+) luminescence of Eu(tta)(3).bpt is higher by 23% than that of Eu(tta)(3).dpbt. Different from the case of Eu(tta)(3).dpbt, Phi(Ln)(L) of Eu(tta)(3).bpt increases linearly with the decrease in temperature. Because of the different coordination environments around Eu(3+) ion, the fine structure of the hypersensitive (5)D(0)-->(7)F(2) emission band of Eu(tta)(3).bpt is quite different from that of Eu(tta)(3).dpbt, with the strongest emission line locating at 620 nm rather than 613 nm where the strongest emission line of Eu(tta)(3).dpbt appears. The excitation window of Eu(tta)(3).bpt is much broader than that of Eu(tta)(3).dpbt with a red edge extending up to 450 nm in a dilute toluene solution (1.0 x 10(-5) M) and 500 nm in a toluene solution (1.0 x 10(-2) M). Eu(tta)(3).bpt also exhibits excellent two-photon-excitation luminescent properties.
    Physical Chemistry Chemical Physics 04/2010; 12(13):3195-202. · 4.20 Impact Factor
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    ABSTRACT: Pure ZnO hexagonal microwires and Fe(III)-doped ZnO microwires (MWs) with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method. An oriented attachment mechanism is consistent with a vapor-solid growth process. Photoluminescence (PL) and Raman spectroscopy of the Fe(III)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(III) along a one-dimensional (1-D) superlattice ZnO:ZnFe2O4 wire, while PL mapping shows the presence of optical multicavities and related multimodes. The PL spectra at room temperature show weak near-edge doublets (376 nm and 383 nm) and a broad band (450–650 nm) composed of strong discrete lines, due to a 1-D photonic crystal structure. Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices.
    Nano Research 01/2010; 3(5):326-338. · 7.39 Impact Factor
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    ABSTRACT: We report an alternative approach, that is, forming Eu(tta)3dpbt (dpbt = 2-( N, N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine, tta = thenoyltrifluoroacetonato) nanoparticles in water/methanol mixtures, to satisfy the combined requirements of good dispersibility in water solutions and efficient long-wavelength sensitization for Eu (III) complexes to be used in biological applications. The size of Eu(tta)3dpbt colloidal particles with very high luminescent capabilities can be modulated to some extent by changing the preparation conditions. The optical excitation window for the Eu (III) luminescence of Eu(tta)3dpbt nanoparticles, extending up to 475 nm, is wider than that of Eu(tta)3dpbt molecules dissolved in toluene. This is the first example for obviously extending the sensitization window of luminescent lanthanide materials to the long-wavelength region by forming nanoparticles of a lanthanide complex. Quantum yields of Eu (III) luminescence of the prepared Eu(tta)3dpbt colloidal particles, with an average diameter of 33.1 nm, are 0.27, 0.27, 0.24, 0.19, 0.14, and 0.01 upon excitation at 402, 420, 430, 440, 450, and 475 nm, respectively. The Eu(tta)3dpbt nanoparticles exhibited excellent two-photon sensitization performance with a highest delta Phi value of 3.2 x 10(5) GM (1 GM = 10(-50) cm4 s photo(-1) particle(-1)) at the excitation wavelength of 832 nm, which is about 7 times higher than the highest value reported for the CdSe/ZnS core-shell quantum dots. The favorable luminescent properties and the good dispersibility in water solutions of the Eu(tta)3dpbt nanoparticles are very promising for the development of new luminescent nanoprobes for bioanalysis.
    Langmuir 08/2008; 24(13):6932-6. · 4.38 Impact Factor
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    ABSTRACT: Using the organic solvent method, nearly mono-dispersed CdS nanocrystals were obtained in liquid paraffin. The CdS nanocrystals in tetrahedron shape capped with the hydrophobic surfactants in nanometer scale can be assembled to a close-packed mono-layered structure. The CdS nanocrystals with different sizes have been prepared by changing the reaction conditions such as the concentrations of cadmium precursor and sulfur precursor, the initial ratio of Cd:S precursors and the pH value of reaction system. The UV–visible absorption and photoluminescence show the quantum confinement effect clearly. The time-resolved photoluminescence spectra have also been examined.
    Optical Materials 06/2004; 26(1):71-74. · 2.08 Impact Factor
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    ABSTRACT: Using nanosecond (ns) and femtosecond (fs) time-resolved absorption spectroscopies (pump–probe technique), the carrier dynamics in transition metal oxide nanocrystals of α-Fe2O3 and ZnFe2O4 was studied during the photolysis process. For Fe2O3 and ZnFe2O4 nanocrystals, the fs measurements detect similar profiles of a positive nonlinear absorption in their capped nanocrystals, whereas much weak signals in the naked particles. In the nanosecond measurements Fe2O3 and ZnFe2O4 nanocrystals show obvious excitation-power dependent absorption properties and at the low pump power they show weak photobleaching, but at high pump power they produce positive nonlinear absorptions. For Fe2O3 nanocrystals, the threshold power of negative absorption (bleach) to positive absorption increases with reducing size, whereas for the ZnFe2O4 samples, the threshold powers reach minimum at a critical size of 11 nm, grow for both the bigger and the smaller nanocrystals. These results reflect the influences of their microscopic magnetic couplings and carrier correlation on biexciton absorption in Fe2O3 and ZnFe2O4 nanocrystals. All the results indicate that the time resolved photoabsorption techniques are useful to study the microscopic spin interactions and carrier correlations in transition metal oxide nanocrystals. © 2004 American Institute of Physics.
    The Journal of Chemical Physics 02/2004; 120(7):3406-3413. · 3.12 Impact Factor
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    ABSTRACT: The chromism of tungsten oxides has been investigated for a long time because of its academic and application importance. In this article the photochromism and its dynamics for a WO3 aqueous sol and WO3−TiO2 mixed sols are studied in detail. The chromic performance of the WO3 aqueous sol is improved significantly by adding TiO2 aqueous sol, and shows a clear size effect. The intrinsic absorption peak at around 777 nm from W5+ in WO3 nanocluster, which generally appears at around 1000 nm in a WO3 film, shifts with cluster size because of the quantum confinement effect of delocalized carriers in WO3 nanoclusters. Besides the 777 nm band from W5+ in WO3, a new extrinsic 640 nm band, due to the transient formation of WOClx species in a WO3 sol in the presence of Cl- and TiO2 nanoclusters, appears after adding TiO2 sol. These results are helpful to the understanding of the chromism of tungsten oxides.
    Chemistry of Materials 10/2003; 15(21):4039-4045. · 8.24 Impact Factor