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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 | Year: 2011

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.


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.
CrystEngComm | Year: 2011

Highly uniform and monodispersed pure hexagonal phase NaReF4 (Re = Y, Pr-Nd, and Sm-Yb) nanocrystals with well-defined morphologies, including pills, rods, spheres, tubes, and plates, were systematically synthesized by a facile solution-based hydrothermal method using oleic acid as a stabilizing agent. Crystal phase, shape and size can be tuned readily by simply adjusting the molar ratio of F/Re and reaction temperature. Detailed experimental studies revealed that NaReF4 hosts strongly tend to form hexagonal phase nanocrystals with increasing rare earth ion radius. Based on the studies on crystal phase control and shape evolution of NaReF4 nanocrystals, the whole growth mechanism of nanocrystals can be concluded as a kinetic and thermodynamic growth process. Simultaneously, highly efficient up-conversion luminescence under 980 nm excitation was realized, such as eye-visible red, green, and blue up-conversion luminescence generated from NaYbF4 host doped with Er3+, Ho3+, and Tm3+, respectively. Due to their unique up-conversion luminescence, the highly uniform and monodispersed nanocrystals can be applied for biolabels, colour displays, light-emitting diodes, and solid-state lasers. © 2011 The Royal Society of Chemistry.


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.
CrystEngComm | Year: 2011

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.


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 | Year: 2010

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.


Ma Y.,Xiangtan University | Ma Y.,Key Laboratory of Low Dimensional Materials and Application Technology | Liu B.,Xiangtan University | Liu B.,Key Laboratory of Low Dimensional Materials and Application Technology | And 4 more authors.
Applied Physics Letters | Year: 2010

Periodic arrays of Ba-O divacancies in BaTiO3 were studied using both first principles calculations and molecular dynamics simulations. It is found that the 2nd -neighbor complexes that are aligned along the direction of the spontaneous polarization have the lowest formation energies. The symmetry between the up and down polarization states is broken, which is manifested by a vertical shift in the polarization-voltage hysteresis loop. Systems containing randomly distributed Ba-O pairs were also studied and the shift in the hysteresis loop is negligible, which suggests that the alignment of polar Ba-O divacancies is responsible for the polarization imprint in ferroelectric BaTiO3. © 2010 American Institute of Physics.


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 | Year: 2010

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.


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 6 more authors.
Journal of Physical Chemistry C | Year: 2010

Here, we present a facile and controlled synthesis of high-quality and uniform hexagonal phase NaYbF4 microtubes by a rational hydrothermal method. In addition, highly uniform and monodisperse NaYbF4 nanospheres and nanocubes are synthesized by simply tuning the reaction parameters, including sodium fluoride content, reaction temperature and reaction time. Under excitation with a 980 nm laser diode, intense ultraviolet (UV) and blue upconversion emissions were achieved from a single dopant ion (Tm 3+) in NaYbF4. The effect of the crystal phase on the upconversion emission properties is also investigated. The results demonstrate that upconversion emission intensities from hexagonal phase NaYbF4 microtubes are much more efficient than the nanocubes by 2 orders of magnitude. These microtubes with unique upconvertion emissions demonstrate that NaYbF 4 is an excellent host material, as compared with some of its other fluoride and oxide counterparts, and that it may find applications in UV and visible solid-state lasers or the fiber lasers. © 2010 American Chemical Society.


Shi Q.,Xiangtan University | Shi Q.,Key Laboratory of Low Dimensional Materials and Application Technology | Ma Y.,Xiangtan University | Ma Y.,Key Laboratory of Low Dimensional Materials and Application Technology | And 4 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2011

Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin films were grown on Pt/Ti/SiO2/Si substrates by a sol-gel method. The samples were exposed to different dosage of ionizing radiation. Distortions in the crystalline structure, changes in the surface roughness and decrease in the remnant polarization were observed after radiation. For films subjected to 100 Mrad radiation, decrease in the leakage current up to four orders of magnitude was also observed, which can be explained by the increased grain boundary barrier height. Our results suggest that ionizing radiation could be an effective tool in modifying the properties of ferroelectric thin film for use in non-volatile memory devices. © 2010 Elsevier B.V. All rights reserved.


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 | Year: 2013

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.


Tang M.H.,Key Laboratory of Low Dimensional Materials and Application Technology | Hou J.W.,Key Laboratory of Low Dimensional Materials and Application Technology | Zhang J.,Key Laboratory of Low Dimensional Materials and Application Technology | Dong G.J.,Key Laboratory of Low Dimensional Materials and Application Technology | Shu W.,Key Laboratory of Low Dimensional Materials and Application Technology
Solid State Communications | Year: 2010

The effect of applied dc bias electric field on dielectric permittivity in bulk La2NiMnO6 is investigated in this paper. It is found that a small bias field of 40 V/cm can greatly reduce the dielectric permittivity around the room temperature, compared to the much larger electric field that is required for conventional ferroelectric materials. The observed giant dielectric tunability is retained over a broad range of around room temperature and is most likely related to the charge ordering of Ni2+ and Mn4+ ions, further confirming the existence of electronic ferroelectricity in La2NiMnO6. © 2010 Elsevier Ltd. All rights reserved.

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