Yichun Liu

Government of the People's Republic of China, Peping, Beijing, China

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Publications (193)467.79 Total impact

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    ABSTRACT: Spirooxazine-doped polymers exhibit a fast photochromism response and high polarization sensitivity after irradiation in the short-wavelength range. Based on such properties, holographic grating recordings accompanying a linearly polarized blue-violet beam (405 nm) in a photochromic film were performed by two coherent green beams (532 nm) for s–s, p–p, s–p left-to-right circular polarization and right-to-right circular polarization. Under the biphotonic action of 405 and 532 nm, the temporal evolution of the diffraction efficiency was strongly dependent on the polarization configuration of the recording beams. It was found that the blue-violet irradiation plays a dual role in holographic recordings: generation of merocyanine aggregation and induction of anisotropy. The experimental results were precisely fitted with a phenomenological model, assuming the simultaneous formation of one absorption grating induced by the 532 nm light and two coupling phase gratings generated from the refractive index changes by recording and auxiliary beams. The existence of absorption and phase gratings was proved by observing the florescence emission of holographic gratings and testing the dependence of the diffraction efficiency on the reading beam polarization state, respectively. The results provided a good deal of insight into the photochromic behavior of spirooxazine in polymers and created a new range of applications in the field of high-density optical storage.
    Applied Optics 09/2014; 53(25). · 1.69 Impact Factor
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    ABSTRACT: Construction of a micro-/nanostructured TiO2 film has been considered to be an important way to enhance the electrochemical properties and electrochromic performance of the material. Herein, we investigated the electrochromic properties of a nanocomposite TiO2 film prepared by decorating rutile a TiO2 nanowire (TiO2 NW) array with anatase TiO2 nanoparticles (TiO2 NPs) via a facile two-step synthesis method. Owing to its large active surface area and high transparency, the TiO2 NW–NP composite film supported a greater number of sites for Li+ ion intercalation and extraction. As a result, the TiO2 NW–NP film displayed higher optical contrast, coloration efficiency and transient current density compared with NW and NP films, demonstrating that enhanced electrochromic properties could be achieved using the NW–NP composite structure.
    J. Mater. Chem. C. 08/2014;
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    ABSTRACT: We successfully synthesized mesoporous ZnxCd1-xS/reduced graphene oxide (ZxCSG) hybrid materials as photocatalysts using a facile one-pot hydrothermal reaction, in which graphene oxide (GO) was easily reduced (RGO), and simultaneously ZnxCd1-xS (ZxCS) nanoparticles (NPs) with a mesoporous structure were uniformly dispersed on the RGO sheets. By well tuning the band gap from 3.42 to 2.21 eV by changing the molar ratio of Zn/Cd (or Zn content), ZxCSG with an optimal zinc content has been found to have a significant absorption in the visible light (VL) region. In addition, under VL irradiation (λ > 420 nm), ZxCSG also showed zinc content-dependent photocatalytic efficiencies for the degradation of methylene blue (MB). Our findings are that, among ZxCSG, Z0.4CSG displayed not only a superior photodegradation efficiency of MB (98%), but also good removal efficiency of total organic carbon (TOC) (67%). Furthermore, Z0.4CSG had a high photocatalytic stability, and could be used repeatedly. The enhanced photocatalytic activity for Z0.4CSG could be attributed to a synergistic effect between mesoporous ZxCS NPs and RGO, including the optimal band gap and the moderate conduction band position for ZxCS (compared to CdS), efficient separation and transfer ability of photogenerated electron/hole pairs in the presence of RGO sheets, and relatively high surface area for both mesoporous ZxCS NPs and RGO.
    Dalton Transactions 07/2014; · 3.81 Impact Factor
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    ABSTRACT: The ordered arrays of CuPc/F16CuPc nanoribbons have been formed by two different methods, an in situ vapor growth method and a pushing transfer method based on vapor grown bundle-like nanoribbons. Low deposition temperatures and low vapor concentrations are critical for the growth of small-size nanoribbons. During the growth process, the external moment of the small-size nanoribbons gradually increases, which helps to bend and adhere the slim nanoribbons to the substrate surface, thus leading to the formation of in situ grown CuPc/F16CuPc single-crystal nanoribbon arrays. On the other hand, based on the commonly observed bundle-like nanoribbons in a high-temperature deposition region, well ordered nanoribbon arrays can be formed by a pushing transfer process. These results show the promising potential for large-scale and high-efficiency fabrication of organic nanowire/nanoribbon transistors.
    J. Mater. Chem. C. 06/2014; 2(28).
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    ABSTRACT: The high ON/OFF ratios of organic single crystal field-effect transistors (FETs) are obtained based on dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (Ph5T2) ultrathin microplates. The ON/OFF ratio is over 108 with a small sweep range of gate voltage (<45 V) in air at room temperature when the dielectric is modified with octadecyltrichlorosilane (OTS). The high ON/OFF ratio is related to the decreased off-state current by molecular design and the increased on-state current by dielectric modification. The ON/OFF ratio up to 1.3 × 107 can also be realized on a flexible transparent substrate. The ultrathin Ph5T2 single crystal provides stable performance even though the flexible device experiences a bending/recovering test for 200 times. The high ON/OFF ratio combined with the high mobility up to 0.51 cm2 V−1 s−1 and the good flexibility of the ultrathin organic single crystals show their promising potential in electronic applications.
    J. Mater. Chem. C. 06/2014; 2(27).
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    ABSTRACT: In this paper, p-MoO3 nanostructures/n-TiO2 nanofiber heterojunctions (p-MoO3/n-TiO2-NF-HJs) were obtained by a two-step fabrication route. First, MoO2 nanostructures were hydrothermally grown on electrospun TiO2 nanofibers. Secondly, by thermal treatment of the obtained MoO2 nanostructures/TiO2 nanofibers, p-MoO3/n-TiO2-NF-HJs were obtained due to the phase transition of MoO2 to MoO3. With increasing the concentration of molybdenum precursor in hydrothermal process, the morphologies of MoO2 changed from nanoparticles to nanosheets, and then fully covered shells with increasing their loading on TiO2 nanofibers. After calcination, the obtained p-MoO3/n-TiO2-NF-HJs possessed similar morphology to that without thermal treatment. X-ray photoelectron spectra showed that both Ti 2p and OTi-O 1s peaks of p-MoO3/n-TiO2-NF-HJs shifted to higher binding energies than that of TiO2 nanofibers, suggesting electrons transfer from TiO2 to MoO3 in the formation of p-n nano-heterojunctions. The p-n nano-heterojunctions decreased photoluminescence intensity, suppressed photogenerated electrons and holes recombinations, and enhanced charge separation and photocatalytic efficiencies. The apparent first-order rate constant for the degradation of RB by p-MoO3/n-TiO2-NF-HJs with nanosheets surface morphology was two times that of TiO2 nanofibers. For the core/shell structure of p-MoO3/n-TiO2-NF-HJs, the internal electric field of p-n junction forced the photo-generated electrons transferring to TiO2 cores, then decreased the surface photocatalytic reactions and led to the lowest photocatalytic activity among the p-MoO3/n-TiO2-NF-HJs.
    ACS Applied Materials & Interfaces 05/2014; · 5.01 Impact Factor
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    ABSTRACT: TiO2/MgO/Au composite thin films with different MgO spacer layer thicknesses (0-41 nm) were fabricated on c-sapphire substrates by sputtering and pulsed laser deposition. Through optimizing the thickness of MgO spacer layer, which can effectively prevent nonradiative Förster resonant energy transfer and charge transfer between Au and TiO2, defect-related yellow-green light emission of TiO2 thin film was greatly enhanced - 12 times. The enhancement mechanism is attributed to the efficient increase of luminescence efficiency of deep levels in TiO2 induced by resonant coupling between localized surface plasmons in Au nanoparticles and electron-hole pairs in defect-related levels of TiO2.
    Journal of Nanoscience and Nanotechnology 05/2014; 14(5):3748-52. · 1.15 Impact Factor
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    ABSTRACT: In this work, we report a novel approach to fabricate hierarchical TiO2 microspheres (HTMS) assembled by ultrathin nanoribbons where an anatase/TiO2(B) heterojunction and high energy facet coexist. The as-adopted approach involves (1) nonaqueous solvothermal treatment of a mixture of tetrabutyl titanate and acetic acid and (2) topotactical transformation into HTMS via thermal annealing. By this approach, the TiO2(B) phase usually synthesized from an alkaline treatment route could be initially formed. Subsequently, phase transition from TiO2(B) to anatase TiO2 occurs upon thermal treatment. It is demonstrated that such phase transition is accompanied by crystallographic orientation along the c-axis of anatase and TiO2(B) crystals, resulting in not only a coherent interface between two phases but also oriented attachment of anatase mesocrystals along the [001] direction, and finally high-energy (001) facet exposure. Interestingly, this work provides an alternative fluorine-free route for the synthesis of TiO2 crystals with high-energy (001) facet exposure. The structural analysis reveals that lattice-match induced topotactic transformation from TiO2(B) to anatase is the sole reason for the (001) facet exposure of anatase TiO2. The photocatalytic test for acetaldehyde decomposition shows that HTMS with anatase/TiO2(B) heterojunction and high-energy (001) facet exhibits superior photocatalytic efficiency compared with the relevant commercial product P25, which can be ascribed to the synergistic effect of large surface area, anatase/TiO2(B) heterojunction as well as high-energy facet exposure.
    Nanoscale 04/2014; · 6.23 Impact Factor
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    ABSTRACT: Wide bandgap (3.37 eV) and high exciton-binding energy of ZnO (60 meV) make it a promising candidate for ultraviolet light-emitting diodes (LEDs) and low-threshold lasing diodes (LDs). However, the difficulty in producing stable and reproducible high-quality p-type ZnO has hindered the development of ZnO p–n homojunction LEDs. An alternative strategy for achieving ZnO electroluminescence is to fabricate heterojunction devices by employing other available p-type materials (such as p-GaN) or building new device structures. In this article, we will briefly review the recent progress in ZnO LEDs/LDs based on p–n heterostructures and metal–insulator-semiconductor heterostructures. Some methods to improve device efficiency are also introduced in detail, including the introduction of Ag localized surface plasmons and single-crystalline nanowires into ZnO LEDs/LDs.
    Chinese Science Bulletin 04/2014; 59(12). · 1.37 Impact Factor
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    ABSTRACT: 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.
    Inorganic Chemistry 03/2014; · 4.59 Impact Factor
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    ABSTRACT: We report a SnO2 nanobelt field effect transistor sensor, with the SnO2:Sb nanobelts serving as the source and drain electrodes. An anomalous feature of the device is that the threshold voltage shows the negative shift upon exposure to NO2. The comparative results from the other two types of devices, including SnO2 nanobelt with metal film electrodes and SnO2:Sb nanobelt with metal film electrodes, reveal that the interface between the SnO2:Sb nanobelt electrodes and the SnO2 nanobelt is responsible for the improved carrier injection efficiency and the negative shift in the threshold voltage. Such a response mechanism results in the detection limit for NO2 down to 10 ppb, with a sensitivity as high as 7.16 × 105 % at room temperature.
    Applied Physics Letters 01/2014; 104(7). · 3.79 Impact Factor
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    ABSTRACT: Phase selective synthesis is particularly valuable in revealing performance of photocatalyst existing as several polymorphic phases. In this work, we develop a general soft chemical route that used a TiO2 (B) nanosheet as a precursor to synthesize TiO2 nanostructures of desired phase. Benefiting from the structural similarity and ultrathin thickness feature, TiO2 (B) nanosheet precursor can readily transform to pure phase of anatase, rutile and brookite as well as mixed phase of brookite/anatase. A possible dissolution-recrystallization mechanism is proposed for the phase transition of TiO2 (B) nanosheets to other phases. Photocatalytic activity tests demonstrated that the brookite/anatase mixture had the highest activity in degrading acetaldehyde under UV light irradiation, due to the synergistic effect of high crystallinity, large surface area and mixed phase structure.
    01/2014;
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    ABSTRACT: TiO2 nanoporous films loaded with Ag nanoparticles exhibited distinctive photochromism and photoanisotropy under the visible linearly polarized irradiation. Based on such properties, a pure polarization holographic grating was recorded in the photochromic film using two orthogonal circularly polarized green beams (532 nm) and reconstructed with a red beam (632.8 nm). The diffraction efficiency of the holographic grating and the brightness of the reconstruction image were strongly dependent on the polarization state of the probe beam. The hologram can be erased simply by the irradiation of single green beam. This recording–erasing process can be repeated with little loss, which may be benefited from the reciprocating mobility of Ag+ ions, reversible deformation and re-growth of Ag nanoparticles under the alternate irradiation of linearly and circularly polarized light. The novel nanocomposite system with photoanisotropy makes a new range of applications in the field of high-density optical memory media.
    Optics Communications 01/2014; 318:1–6. · 1.44 Impact Factor
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    ABSTRACT: The construction of multiple heterojunctions holds promise for enhancing the performance of semiconducting photocatalysts. It can improve charge separation and extend light absorption range via component optimization. Herein, we report the structural design and optimization of a (WO3–Pt)/TiO2 multi-heterojunction photocatalyst based on WO3 nanorods and Pt and TiO2 nanoparticles. The multi-heterojunction-based photocatalyst displayed high activity for the degradation of Rhodamine B dye (RB), phenol, and gaseous acetaldehyde under visible light excitation. Moreover, its activity was higher than single-heterojunction-based photocatalysts, P25 and P25/Pt. The higher performance of the multi-heterojunction-based photocatalyst was attributed to the synergistic effect of efficient conduction band electrons transfer at the WO3/Pt interface and valence band holes transfer at the WO3/TiO2 interface. The photocatalytic performance of the multi-heterojunction-based photocatalyst was also dependent on the location of the loaded Pt nanoparticles. Pt surface loading on WO3, as opposed to loading on the TiO2 surface, was more beneficial in maximizing the photocatalytic activity.
    Chemical Engineering Journal. 01/2014; 237:29–37.
  • Electrochimica Acta. 01/2014; 130:290–295.
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    ABSTRACT: Bi2WO6–carbon nanofibers (Bi2WO6–CNFs) heteroarchitectures were fabricated by two steps consisting of the preparation of CNFs by electrospinning and growth of Bi2WO6 on the CNFs through ethylene glycol solvothermal processing. The results showed that the loading amounts of Bi2WO6 on the surface of CNFs could be controlled by adjusting the precursor concentration for the fabrication of Bi2WO6–CNFs heteroarchitectures during the solvothermal process. The photocatalytic tests revealed that the obtained Bi2WO6–CNFs heteroarchitectures showed higher photocatalytic property under visible light to degrade Rhodamine B than pure Bi2WO6 synthesized by solvothermal process in the absence of CNFs owing to improved separation efficiency of photogenerated electrons and holes. Moreover, the Bi2WO6–CNFs heteroarchitectures could be separated easily by sedimentation due to their one-dimensional nanostructural property. Meanwhile, the photocatalytic activity of Bi2WO6–CNFs heteroarchitectures was stable during the recycling due to the strong interactions between Bi2WO6 nanosheets and CNFs. Trapping experiment suggested that [TEX equation: {\text{O}}_{ 2}^{ \cdot - }] , instead of OH·, was the main active species during the photocatalytic process of the Bi2WO–CNFs heteroarchitectures.
    Journal of Sol-Gel Science and Technology 01/2014; 70(1). · 1.66 Impact Factor
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    ABSTRACT: Recently; one-dimensional (1D) nanostructure field-effect transistors (FETs) have attracted much attention because of their potential application in gas sensing. Micro/nanoscaled field-effect sensors combine the advantages of 1D nanostructures and the characteristic of field modulation. 1D nanostructures provide a large surface area-volume ratio; which is an outstanding advantage for gas sensors with high sensitivity and fast response. In addition; the nature of the single crystals is favorable for the studies of the response mechanism. On the other hand; one main merit of the field-effect sensors is to provide an extra gate electrode to realize the current modulation; so that the sensitivity can be dramatically enhanced by changing the conductivity when operating the sensors in the subthreshold regime. This article reviews the recent developments in the field of 1D nanostructure FET for gas detection. The sensor configuration; the performance as well as their sensing mechanism are evaluated.
    Sensors (Basel, Switzerland). 01/2014; 14(8):13999-14020.
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    ABSTRACT: A multiple drop-casting method of growing the ultralong dibenzo-tetrathiafulvalene (DB-TTF) micro/nanowire arrays has been developed which has the success ratio as high as 94%. This method enables the arrays with a length over a few hundreds of micrometers to locate between droplets with the definite orientation. The width of the micro/nanowires is controlled via tuning the concentration of DB-TTF solution in dichloromethane. The large-scale arrays can be grown onto Si, SiO2, glass, and the flexible polyethylene terephthalate (PET) substrates. These results show the promising potential of this facile solution-based process for the growth of the high-quality organic micro/nanowires, the fabrication of high-performance and flexible devices, and the fabrication of controlled assemblies of nanoscale circuits for fundamental studies and future applications.
    Nanoscale 12/2013; · 6.23 Impact Factor
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    ABSTRACT: In this work, a series of n-ZnO/p-GaN and n-MgZnO/p-GaN heterojunctions are designed and fabricated. The carrier transport and recombination mechanism is discussed based on electroluminescence (EL) and photoluminescence (PL) spectra, current–voltage (I–V) characteristics as well as energy band diagram. For ZnO device, the near-ultraviolet (UV) emission at ∼400 nm is attributed to the spatially-indirect, interfacial transition from ZnO conduction band minimum to GaN acceptor level. While for MgZnO diodes, their UV EL is independent on Mg composition, is thought to origin from the donor–acceptor pair (DAP) recombination in GaN layer. Our experiment results suggest that pure ZnO or MgZnO emission can hardly be achieved in n-(Mg)ZnO/p-GaN heterojunctions, rational device design towards (Mg)ZnO exciton emission is more important in the further work. EL spectra of different n-MgxZn1−xO/p-GaN diodes and the schematic carrier transport and recombination process.
    Physica Status Solidi (A) Applications and Materials 12/2013; 210(12). · 1.46 Impact Factor
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    ABSTRACT: A new approach has been proposed and validated to modulate the emission spectra of europium-doped 12CaO·7Al2O3 phosphors by tuning the nonradiative and radiative transition rates, realized by controlling the sort and amount of the encaged anions. A single wavelength at 255 nm can excite simultaneously Eu2+ and Eu3+ centres to yield blue and red emissions, respectively. The amount of the anions in the nanocages, like OH− and H−, can be controlled by heat treatment processes. The existence of encaged OH− accelerates the nonradiative process of the emission centres, while the presence of encaged H− induces a higher symmetry that decreases the radiative transition rate, confirmed by the analysis of decay processes. It is demonstrated that the emission colour is tuned finely from red to blue with the CIE chromaticity coordinates from (0.630, 0.352) to (0.216, 0.086) when the annealing time increases. This strategy can be readily extended to similar systems with other rare earth active centres.
    J. Mater. Chem. C. 11/2013; 1(47).

Publication Stats

763 Citations
467.79 Total Impact Points

Institutions

  • 2014
    • Government of the People's Republic of China
      Peping, Beijing, China
  • 2000–2014
    • Northeast Normal University
      • • Center for Advanced Optoelectronic Functional Materials Research
      • • Department of Chemistry
      Hsin-ching, Jilin Sheng, China
  • 2012
    • Beihua University
      Yung-chi, Jilin Sheng, China
  • 2011
    • Changchun University of Technology
      Huinan, Jilin Sheng, China
  • 2002–2009
    • Changchun Institute of Optics, Fine Mechanics and Physics
      Hsin-ching, Jilin Sheng, China
  • 2007
    • Jilin University
      • College of Electronic Science and Engineering
      Jilin, Jilin Sheng, China
  • 2006
    • Fisk University
      • Department of Physics
      Nashville, TN, United States
  • 2005
    • Nanjing University
      • Department of Physics
      Nanjing, Jiangsu Sheng, China