Hancheng Zhu

Northeast Normal University, Hsin-ching, Jilin Sheng, China

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Publications (7)18.97 Total impact

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    ABSTRACT: Long lasting blue emitting Eu-doped 12CaO⋅7Al2O3 thin films have been prepared on quartz substrates by pulsed laser deposition combined with post-annealing. The 12CaO⋅7Al2O3 phase is formed after annealing the films above 900 °C in vacuum ambient. Upon 323 nm excitation, the thin films exhibit a blue long lasting emission peaked at 444 nm, assigned to the 5d–4f transitions of Eu2+. The films annealed at 950 °C have stronger luminescence and longer lasting time than that annealed at 900 °C. The phosphorescence intensity of vacuum annealed film is better than that annealed in H2/N2 atmosphere, which might be due to the increase of shallow trap numbers during the vacuum annealing process. Thermoluminescence curves demonstrate that vacuum and H2/N2 atmosphere annealing could introduce a large number of both shallow and deep traps into 12CaO⋅7Al2O3:Eu thin films. After UV irradiation, excellent photostimulated luminescence can be observed under 980 nm excitation. Our results suggest that 12CaO⋅7Al2O3:Eu phosphor may serve as a promising blue luminescent materials used in fabrication of optical storage and illumination in dark environments.
    Optical Materials 09/2014; · 2.08 Impact Factor
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    ABSTRACT: In this work, novel upconversion lanthanide oxyfluoride (LnOF:Yb3+, Er3+, Ln = La, Y, Gd) inverse opal photonic crystals (IOPCs) were successfully fabricated by the sol–gel method combined with polymethylmethacrylate (PMMA) template technique and the modulation of the photonic stop band (PSB) on the green emissions 2H11/2/4S3/2 → 4I15/2 for Er3+ ions were systemically studied under 980 nm excitation. The results showed that the LaOF IOPCs (annealed at 500 °C) were of cubic phase while GdOF and YOF matrices were of rhombohedral phase, and the LaOF IOPCs demonstrated more efficient upconversion luminescence (UCL) than GdOF and YOF due to the phase transition. In contrast to the ground reference (REF) samples, strong suppression of UCL was observed in the IOPCs while the PSB overlapped with the 2H11/2/4S3/2 → 4I15/2 lines. Furthermore, the spontaneous decay rates (SDRs) of 2H11/2/4S3/2 → 4I15/2 were suppressed in the IOPCs, independent of the location of the PSB. In LaOF IOPCs, the decay time constants of 4S3/2 → 4I15/2 were increased by as much as 9 times in contrast to the corresponding REFs. It was also significant to observe that in the IOPCs the local thermal effect was greatly suppressed. In addition, broadband UCL extending into the visible range was observed in LnOF:Yb3+, Er3+ REF samples under high excitation power, and the origin was identified by electron paramagnetic resonance (EPR) spectroscopy.
    J. Mater. Chem. C. 05/2014; 2(21).
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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).
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    ABSTRACT: A multiphase strategy is proposed and successfully applied to make the insulating green phosphor CaCeAl3O7:Tb(3+) conductive in the form of 12CaO·7Al2O3-CaCeAl3O7:Ce(3+),Tb(3+). The phosphor shows bright green-light emission with a short lifetime (2.51 ms) under low-voltage electron beam excitation (3 kV). The green photo- and cathodoluminescence from (5)D4-(7)FJ (J = 6, 5, 4, 3) transitions of Tb(3+) are significantly enhanced in comparison with pure C12A7:Tb(3+). It was confirmed that this enhancement is the consequence of the joint effects of energy transfer from Ce(3+) to Tb(3+) and broadening of the absorption spectrum of Ce(3+) due to the existence of multiple phases. In particular, under 800 V electron beam excitation, cathodoluminescence is improved by the modified electrical conductivity of the phosphor. When compared to the commercial Zn2SiO4:Mn(2+) with a long luminescence lifetime of 11.9 ms, this conductive green phosphor has greater advantage for fast displays.
    Dalton Transactions 09/2013; · 3.81 Impact Factor
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    ABSTRACT: A novel white-light-emitting phosphor, 12CaO·7Al2O3:Ce3+, Dy3+with H− encaging, was prepared by the solid-state reaction in H2 atmosphere. Upon excitation at 362 nm, the phosphor shows intense white-light emission that combines the blue and yellow emissions at 476 and 576 nm, assigned to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. A weak broad blue emission centered at 430 nm is also observed and attributed to the 5d–4f transitions of Ce3+. The photoluminescence intensity of Dy3+ increases greatly with increasing Ce3+ concentration, indicating that the effective energy transfer occurred from Ce3+ to Dy3+ in the phosphor. In particular, the phosphor can be converted to a persistent semiconductor upon ultraviolet irradiation due to the electrons released from the encaged H− ions, and the electrical conductivity is measured to be 10−2 S cm−1. The conductive phosphor exhibits excellent white-light emission (CIE coordinate of (0.324, 0.323)) under low-voltage (5 kV) electron beam excitation, suggesting that the phosphor is a potential candidate for applications in field emission displays.
    Journal of Materials Chemistry 07/2012; 22(33):16839-16843. · 5.97 Impact Factor
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    ABSTRACT: 12CaO 7Al2O3:Dy3+ nanopowders were successfully synthesized by the chemical co-precipitation method. X-ray diffraction result shows that the single 12CaO 7Al2O3 phase is formed with Dy3+ ions to replace the Ca2+ ions in the host of 12CaO 7Al2O3. The yellow and blue emissions, attributed to the forced electric dipole transition of 4F(9/2) --> 6H(13/2) centered at 571 nm and the magnetic dipole transition of 4F(9/2) --> 6H(15/2) centered at 480 nm, respectively, were observed. The integrated intensity ratios of yellow to blue increase from 1.63 to 1.70 with Dy3+ concentration increasing from 0.8 to 2.0% for the as-prepared 12CaO 7Al2O3:xDy3+ phosphor. The significantly enhanced emission intensities of 12CaO 7Al2O3:1.0% Dy3+ phosphor annealed at 900 degrees C for 2 hours in vacuum ambient could be ascribed to the decrease of OH(-) groups and the change of the surface topography. The thermal stability and the Commission International de l'Eclairage coordinates were also investigated. All the photoluminescence characteristics indicate that Dy3+ ions doped 12CaO 7Al2O3 may be a good candidate for the solid state lighting phosphor as well as white light-emitting diodes.
    Journal of Nanoscience and Nanotechnology 11/2011; 11(11):9958-63. · 1.15 Impact Factor
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    ABSTRACT: The irradiation of ultraviolet (UV) light usually induces the photodegradation of organic photovoltaic materials, leading to the significant degeneration of organic photovoltaic (OPV) solar cells. In view of this, we designed UV to visible photo-conversion YVO4: Eu3+, Bi3+ nano-films for the first time. These nano-films could not only filter out the harmful UV light to improve the lifetime of OPV, but also enhanced the power conversion efficiency (PCE). In this paper, we present the preparation, structure and excellent photoconversion properties of Y0.97−xVO4:0.03Eu3+, xBi3+ (0 ≤ x ≤ 0.4) microsized powders and the nano-film converters fabricated by laser ablation. Furthermore, the photo-stability of P3HT film with the converter was investigated. It is exciting to observe that the degradation of P3HT thin-film can be effectively retarded with the converter, about 3 fold compared to that of the glass reference. The photoconverter from UV to visible has the potential to be practically used in future OPV solar cells devices.
    Journal of Materials Chemistry 08/2011; 21(33):12331-12336. · 5.97 Impact Factor