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Ma M.,Xiangtan University | Xu C.,Xiangtan University | Xu C.,Key Laboratory of Low Dimensional Materials and Application Technology | Yang L.,Xiangtan University | And 3 more authors.
Physica B: Condensed Matter

Stoichiometric Y7O6F9 powder codoped with Yb3Tm3 was synthesized via co-precipitation and subsequent calcining route. The results of X-ray diffraction and transmission electron microscopy reveal that when the calcining temperature is beyond 800 °C, orthorhombic YF3 nanoparticles can be completely oxidized into orthorhombic Y7O6F9 powder. Under the excitation of a 980 nm laser, Y7O6F9 powder exhibits multicolor UC emission in regions spanning the UV to the NIR. In addition, the upconversion emission intensities of YF3, Y 7O6F9 and Y2O3 powders were compared under the same dopant condition (Yb/Tm=5/0.5 mol%). The low phonon energy revealed by Raman spectra helped to understand the high efficient upconversion emission of Y7O6F9 and the main phonon vibration of Y7O6F9 lies at 472 cm -1, which is far lower that of Y2O3 (at 708 cm-1). Our results indicate that orthorhombic rare earth ions doped Y7O6F9 is an efficient matrix for UV and blue UC emission, and has potential applications in color displays, anti-counterfeiting and multicolor fluorescent labels. © 2011 Elsevier B.V. All rights reserved. Source

Zhang Y.,Xiangtan University | Zhong X.L.,Xiangtan University | Zhong X.L.,Key Laboratory of Low Dimensional Materials and Application Technology | Wang J.B.,Xiangtan University | And 3 more authors.
Applied Physics Letters

Metal-ferroelectric-insulator-silicon diodes with Bi3.15 Nd 0.85 Ti3 O12 (BNT) as the ferroelectric layer and Y2 O3 -stabilized ZrO2 (YSZ) as the insulating buffer layer have been fabricated. Measurements revealed that the memory window of the fabricated diode reduces with increasing operating temperature, which is due to the decrease of coercive field and polarization of the BNT film. The diode demonstrates excellent retention and fatigue characteristics because of the good interface and high barrier height of YSZ/Si. In addition, the switching of the diode corresponds to an approximate constant-current process, and the complete switching time displays an obvious decrease as the gate voltage increases. © 2010 American Institute of Physics. Source

Liu B.,Xiangtan University | Ma Y.,Xiangtan University | Ma Y.,Key Laboratory of Low Dimensional Materials and Application Technology | Zhou Y.,Xiangtan University | And 2 more authors.
Radiation Effects and Defects in Solids

Bi3.15Nd0.85Ti3O12 (BNT) thin films have been deposited onto Pt/Ti/SiO2/Si substrates by chemical solution deposition. Pt top electrodes were then deposited to form the capacitor structure (Pt/BNT/Pt). The prepared capacitors were subjected to 1×1015 n/ cm2 neutron radiation. Loss in the remanent polarization and changes in the leakage current characteristics were observed after radiation. Possible mechanisms concerning the radiation-induced changes were discussed. The increased pinning of domain wall was identified as the primary reason for polarization loss, while the decreased barrier height resulted in the increased leakage current. © 2013 Copyright Taylor and Francis Group, LLC. Source

Zeng S.,Xiangtan University | Zeng S.,Key Laboratory of Low Dimensional Materials and Application Technology | Ren G.,Xiangtan University | Ren G.,Key Laboratory of Low Dimensional Materials and Application Technology | And 2 more authors.
Journal of Materials Chemistry

A novel Er3+ doped NaYbF4 hexagonal-prismatic micro-tubular structure with single crystalline nature was synthesized by a facile hydrothermal method. The typical morphologies and structure were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) which revealed that the as-prepared samples presented a tubular structure with open ends and uniform size. Based on TEM analysis of the samples prepared at different hydrothermal treatment times, the formation mechanism of the NaYbF4 hexagonal-prismatic micro-tube was concluded to be that the nano-sized clusters nucleated first and then self-assembly aggregated into thin sheets and finally rolled into NaYbF4 hexagonal-prismatic micro-tubes. Intense red upconversion luminescence was observed by the naked eye under 980 nm excitation, which indicated that the novel NaYbF4 micro-tubular structure is a potential host material for photoluminescence. Due to the unique luminescence, these NaYbF4 hexagonal-prismatic micro-tubes may be promising for further fundamental research and find applications in color displays and solid-state lasers. © 2010 The Royal Society of Chemistry. Source

Zeng S.,Xiangtan University | Zeng S.,Key Laboratory of Low Dimensional Materials and Application Technology | Ren G.,Xiangtan University | Ren G.,Key Laboratory of Low Dimensional Materials and Application Technology | And 4 more authors.

In this paper, a simple lanthanide (Ln) doping route for modifying the crystal structure including crystal phase, shape, size and physics properties such as up conversion (UC) and magnetic properties of monodisperse multifunctional NaYbF4 nanocrystals is demonstrated. The results revealed that the crystal phase transformation from cubic to hexagonal phase, shape evolution from one-dimensional (rods) to zero-dimensional (nanoparticle) and size transition from microscale to nanoscale can be readily tuned. Moreover, these nanocrystals doped with different Gd3+ concentrations exhibit multi-functionality, including tunable UC emissions colours and paramagnetic properties, which making them potentially applicable in the biological field as biolabels, bioseparation, magnetic resonance imaging (MRI), and optical-magnetic dual modal nanoprobes in biomedical imaging. It is also expected that the doping-induced structure and physical properties transformation can be applied to other NaLnF4 nanocrystals. © 2011 The Royal Society of Chemistry. Source

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