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Sun J.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | Sun J.,Hebei University of Technology | Ding D.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | Ding D.,Hebei University of Technology | Sun J.,Beijing Technology and Business University
Optical Materials | Year: 2016

Sr3-2xSmxNaxB2SiO8 phosphors were synthesized by the solid-state reactions. X-ray diffraction, diffuse reflection, photoluminescence excitation and emission, as well as fluorescence decay measurements were utilized to investigate the structural and spectral properties of the samples. The results indicated that Sr3-2xSmxNaxB2SiO8 phosphors could be efficiently excited by the near-ultraviolet light to realize a novel reddish orange luminescence corresponding to the characteristic transitions 4G5/2→6HJ (J = 5/2, 7/2, 9/2, 11/2) of Sm3+ ions, with a maximum intensity at 600 nm. Based on the theoretical calculation, the dipole-dipole interaction was dominantly involved concentration quenching of Sm3+ in the phosphors, and the critical transfer distance (Rc) was determined to be 13.59 Å. Furthermore, Judd-Ofelt analysis was applied to evaluate three phenomenological Judd-Ofelt intensity parameters (Ωλ, λ = 2, 4, 6), and in turn radiative properties such as radiative transition probabilities (AR), radiative lifetimes (τR) and fluorescence branching ratios (βR) for the excited 4G5/2 luminescent level of Sm3+ ions were determined. Upon 402 nm excitation, the composition-optimized Sr2.90Sm0.05Na0.05B2SiO8 exhibited the preferable photoluminescence intensity and CIE coordinates of (0.534, 0.448). These results suggest that the Sm3+-doped Sr3B2SiO8 phosphors are competitive as the reddish orange-emitting phosphor-converted materials for application in near-ultraviolet-pumped LEDs. © 2016 Elsevier B.V.

Zhao N.,Hebei University of Technology | Li Y.,Hebei University of Technology | Zhi X.,Hebei University of Technology | Wang L.,Hebei University of Technology | And 5 more authors.
Journal of Rare Earths | Year: 2016

LiFe1-xCexPO4/C cathode materials were synthesized by solid-state reaction method. The effects of various Ce-doping amounts on the microstructure and electrochemical performance of LiFePO4/C cathode material were intensively investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge-discharge measurements and electrochemical impedance spectroscopy (EIS). The results indicated that Ce-doping did not destroy the lattice structure of LiFePO4/C, while enlarged the lattice volume tailored the particle size, decreased charge transfer resistance, increased electrical conductivity and Li-ion diffusion rate of LiFePO4/C, and thus markedly enhanced the electrochemical performance of the LiFePO4/C. Electrochemical test results showed that the LiFe0.9Ce0.1PO4/C sample exhibited the best electrochemical performance with initial specific capacity of 155.4 mAh/g at 0.2 C, the capacity retention ratios of 99.6% at 100 cycles at 1 C and delivered a discharge capacity of 160.1 (0.1 C), 156.6 (0.2 C), 151.2 (0.5 C), 147.6 (1 C), 140.7 (2 C) and 136.7 mAh/g (5 C), respectively, presented the best rate capacity among all the samples. EIS results demonstrated that the transfer resistance of the sample decreased greatly by doping an appropriate amount of Ce. © 2016 The Chinese Society of Rare Earths.

Zhang H.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | Zhang H.,Hebei University of Technology | Liang J.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | Liang J.,Hebei University of Technology | And 4 more authors.
Materials Letters | Year: 2016

Because of the biomimetic structure and bioactivity preservation, coaxial electrospinning was applied to prepare fibrous scaffolds for delivery growth factors. In this investigation, the coaxial electrospinning technique was modified with emulsion or chitosan hydrogel as the core, to control the release of basic fibroblast growth factor (bFGF). Compared with the conventional coaxial electrospun sample, the emulsion-core coaxial electrospun samples reduced the release amount to around 25% in the first stage, while the hydrogel-core coaxial electrospun sample increased to 63.59% in the first 7 days; and the bFGF cumulative release of all the improved coaxial electrospun samples could achieve about 90%, which was much higher than the control sample (59.89%). Though the appropriate components in the core and the degradation degree of fibres, the modified coaxial electrospun membranes could modulate the release behavior of growth factors following the desired rate and amount, which is beneficial to regeneration of several tissue types. © 2016 Elsevier B.V. All rights reserved.

Wang L.,Hebei University of Technology | Wang L.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | Liu G.,Hebei University of Technology | Liu G.,Key Laboratory of Special Functional Materials for Ecological Environment and Information | And 6 more authors.
Journal of Materials Chemistry A | Year: 2015

The high voltage spinel LiNi0.5Mn1.5O4 with a peanut-like morphology and porous structure was synthesized by an ethylene glycol-assisted hydrothermal method using urea as a precipitant followed by high-temperature calcination. For comparison, the LiNi0.5Mn1.5O4 sample was also synthesized in the aqueous solution in the absence of ethylene glycol (EG). The as-prepared materials were characterized by XRD, SEM, TEM, FT-IR, CV, EIS and galvanostatic charge/discharge tests. The presence of EG in the hydrothermal process improves the dispersity and decreases the particle size of the final LiNi0.5Mn1.5O4 product, thus leading to its better rate capability, whose discharge capacity at a 10C rate could reach as high as 121.4 mA h g-1. On the other hand, the presence of EG in the hydrothermal process could make the reagents mix more homogeneously, thus leading to higher crystallinity, lower impurity and Mn3+ contents, which are advantageous to the cycling performance. Furthermore, the porous structure of the LiNi0.5Mn1.5O4 material could effectively mitigate the volume change caused by the repeated Li+ insertion/extraction process, which is also conducive to the cycling stability. The LiNi0.5Mn1.5O4 cathode material synthesized by the EG-assisted hydrothermal process shows a capacity retention rate of 96.4% after 100 cycles at a 1C rate. Additionally, a possible formation mechanism for the Ni0.25Mn0.75CO3 precursor with a peanut-like morphology was also proposed. © The Royal Society of Chemistry.

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