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1.
A novel red long lasting phosphorescent materials β-Zn3(PO4)2:Mn2+,Sm3+ is firstly synthesized by high-temperature solid-state reaction. The influence of Sm3+ ions on luminescence and long lasting phosphorescence properties of Mn2+ in phosphor β-Zn3(PO4)2:Mn2+,Sm3+ are systematically investigated. It is found that the red phosphorescence (λ = 616 nm) performance of Mn2+ ion such as brightness and duration is largely improved when Sm3+ ion is co-doped into the matrix in which Mn2+ ion acts as luminescent center and Sm3+ ion plays an important role of electron trap. Thermoluminescence spectrums show that there exists one peak in β-Zn3(PO4)2:Mn2+,Sm3+, the depth of which is 0.33 eV, and that there are three peaks in β-Zn3(PO4)2:Mn2+, among which the depth of the lowest temperature peak in β-Zn3(PO4)2:Mn2+ is 0.37 eV. Such differences in the trap depth result in the improvement of red long lasting phosphorescence of Mn2+ in present matrix.  相似文献   

2.
A new lithium iron(III) phosphate, Li9Fe7(PO4)10, has been synthesized and is currently under electrochemical evaluation as an anode material for rechargeable lithium-ion battery applications. The sample was prepared via the ion exchange reaction of Cs5K4Fe7(PO4)101 in the 1 M LiNO3 solution under hydrothermal conditions at 200 °C. The fully Li+-exchanged sample Li9Fe7(PO4)102 cannot yet be synthesized by conventional high-temperature, solid-state methods. The parent compound 1 is a member of the Cs9−xKxFe7(PO4)10 series that was previously isolated from a high-temperature (750 °C) reaction employing the eutectic CsCl/KCl molten salt. The polycrystalline solid 1 was first prepared in a stoichiometric reaction via conventional solid-state method then followed by ion exchange giving rise to 2. Both compounds adopt three-dimensional structures that consist of orthogonally interconnected channels where electropositive ions reside. It has been demonstrated that the Cs9−xKxFe7(PO4)10 series possesses versatile ion exchange capabilities with all the monovalent alkali metal and silver cations due to its facile pathways for ion transport. 1 and 2 were subject to electrochemical analysis and preliminary results suggest that the latter can be considered as an anode material. Electrochemical results indicate that Li9Fe7(PO4)10 is reduced below 1 V (vs. Li) to most likely form a Fe(0)/Li3PO4 composite material, which can subsequently be cycled reversibly at relatively low potential. An initial capacity of 250 mAh/g was measured, which is equivalent to the insertion of thirteen Li atoms per Li9+xFe7(PO4)10 (x = 13) during the charge/discharge process (Fe2+ + 2e → Fe0). Furthermore, 2 shows a lower reduction potential (0.9 V), by approximately 200 mV, and much better electrochemical reversibility than iron(III) phosphate, FePO4, highlighting the value of improving the ionic conductivity of the sample.  相似文献   

3.
LiMxMn2−xO4 (M = Ni2+, Co3+, and Ti4+; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge-discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge-discharge tests showed that as-prepared LiMn2O4 could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95-3.5 V, the materials showed much better electrochemical performances than LiMn2O4 in terms of capacity, cycleability and rate capability.  相似文献   

4.
New Ce3+ and/or Mn2+ activated Ca10K(PO4)7 phosphors were prepared by solid-state reaction, and their photoluminescence properties upon ultraviolet and vacuum ultraviolet excitation were investigated. Under 254 nm excitation, a series of Ca10K(PO4)7:xMn2+ samples exhibit two emission bands at 463 and 650 nm, which could be attributed to oxygen defects and 4T16A1 transition of Mn2+, respectively. And an energy transfer from defects to Mn2+ has been observed. With the Mn2+ content increased, the emitting hues of Ca10K(PO4)7:Mn2+ can range from blue to red. By co-doping Ce3+ to Ca10K(PO4)7:Mn2+, the emission intensity of Mn2+ is strongly enhanced due to an efficient energy transfer by [Ce3+ → Mn2+] and [defects → Ce3+ → Mn2+]. But under 147 nm excitation, the emission intensity of Mn2+ in Ca10K(PO4)7:0.25Mn2+ decreases slightly compared with that in Ca10K(PO4)7:025Mn2+, 0.1Ce3+, 0.1K+ due to the host sensitization competition between Ce3+ and Mn2+.  相似文献   

5.
LiCo1−xMxPO4 (M = Mg2+, Mn2+ and Ni2+; 0 ≤ x ≤ 0.2) compounds have been synthesized by solid-state reaction method and studied as cathode materials for secondary lithium batteries. LiCoPO4 exhibits a discharge plateau at ∼4.7 V with an initial discharge capacity of 125 mAh/g and on cycling capacity falls. Substitution of Co2+ with Mg2+/Mn2+/Ni2+ in LiCoPO4 has an influence on the initial discharge capacity and on cycling behaviour. The capacity retention of LiCoPO4 is improved by manganese substitution. Among the manganese substituted phases, LiCo0.95Mn0.05PO4 shows good reversible capacity of ∼50 mAh/g.  相似文献   

6.
The electrochemical performance of LiMn2O4 is improved by the surface coating of nano-Li3PO4 via ball milling and high-temperature heating. The Li3PO4-coated LiMn2O4 powders are characterized by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). At 55 °C, capacity retention of 85% after 100 cycles was obtained for Li/Li3PO4-coated LiMn2O4 electrode at 1C rate, while that of pristine sample was only 65.6%. The Li/Li3PO4-coated LiMn2O4 electrode also showed improved rate capability especially at high C rates. At 5C-rates, the delivered capacities of pristine and Li3PO4-coated LiMn2O4 electrodes were 80.7 mAh/g and 112.4 mAh/g, respectively. The electrochemical impedance spectroscopy (EIS) indicates that the charge transfer resistance for Li/Li3PO4-coated LiMn2O4 cell was reduced compared to Li/LiMn2O4 cell.  相似文献   

7.
Novel Tb3+ and Mn2+ activated Ca8MgGd(PO4)7 phosphors were synthesized by solid-state reaction and their photoluminescence properties in vacuum ultraviolet region were investigated for the first time. It can be observed from the excitation spectra that the host-related absorption band is located around 170 nm, and it overlaps the O2− → Tb3+ charge transfer band of Ca8MgGd(PO4)7:Tb3+ around 161 nm and the 3d5 → 3d44s transition band of Ca8MgGd(PO4)7:Mn2+ near 200 nm. The 4f-4f 5d spin-allowed and spin-forbidden transitions of Tb3+ are verified to be located at 170-250 and 257-271 nm, respectively. Upon 147 nm excitation, the dominant emission peak intensity of the Ca8MgGd0.1(PO4)7:0.9Tb3+ phosphor is about 2.7 times stronger than that of the commercial Zn2SiO4:Mn2+ green phosphor, and the brightness of the former with a short decay time of 2.5 ms is about 98% of the latter’s. The Ca8MgGd(PO4):Mn2+ phosphor excited at 147 nm exhibits a deep red emission around 650 nm, which could be attributed to the 4T1 → 6A1 transition of Mn2+, with the CIE index (0.679, 0.321). In a word, the results above indicate that both Tb3+ and Mn2+ activated Ca8MgGd(PO4)7 phosphors could be promising for PDP or Hg-free lamp applications.  相似文献   

8.
The polycrystalline samples of Fe3−xMnxO4 (0.10 ≤ x ≤ 0.50) were prepared by a solid-state route reaction method. X-ray diffraction pattern shows that Mn2+ doped magnetites are in single phase and possess cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirms the first order phase transition at the Verwey transition TV = 123 K and 117 K, respectively. No first order phase transition was evidenced for Fe3−xMnxO4 (0.10 ≤ x ≤ 0.50). Small polaron model has been used to fit the semiconducting resistivity behavior and the activation energy ?a, for samples x = 0.10 and 0.50 is about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe3−xMnxO4 at room temperature reveal five phonons modes for Fe3−xMnxO4 (0.01 ≤ x ≤ 0.50) as expected for the magnetite (Fe3O4). Increased Mn2+ doping at Fe site leads to a gradual changes in phonon modes. The Raman active mode for Fe3−xMnxO4 (x = 0.50) at ≅641.5 cm−1 is shifted as compared to parent Fe3O4 at ≅669.7 cm−1, inferring that Mn+2 ions are located mostly on the octahedral sites. The laser power is fixed to 5 mW causes the bands to broaden and to undergo a small shift to lower wave numbers as well as increase in the full width half maxima for A1g phonon mode with the enhancement of Mn2+ doping. Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Mn+2 ions are located mostly on the octahedral sites of the Fe3−xMnxO4 spinel structure.  相似文献   

9.
Fluorine-doped 5 V cathode materials LiNi0.5Mn1.5O4−xFx (0.05 ≤ x ≤ 0.2) have been prepared by sol-gel and post-annealing treatment method. The results from X-ray diffraction and scanning electron microscopy (SEM) indicate that the spinel structure changes little after fluorine doping, but the particle size varies with fluorine doping and the preparation conditions. The electrochemical measurements show that stable cycling performance can be obtained when the fluorine amount x is higher than 0.1, but the specific capacity is decreased and 4 V plateau capacity resulting from a conversion of Mn4+/Mn3+ remains. Moreover, influence of the particle size on the reversible capacity of the electrode, especially on the kinetic property, has been examined.  相似文献   

10.
LiFexMn1-xPO4 (x?=?0?~?1) cathode materials were widely studied in the past few years. The results show that this olivine-structured material would present higher energy density that can be achieved at higher Mn content. However, the specific capacity and rate capability of the LiFexMn1-xPO4 would decrease with decrease of x from results of various studies. Here, we chose the optimal x value of 0.3 and successfully synthesized the pure LiMn0.7Fe0.3PO4 via microwave-solvothermal method at 200°C with a short reaction time of 10?min. In spite of the low synthesis temperature, the as-synthesized powders with thinner thickness along [010] direction are highly crystalline. Sample exhibited excellent rate capability and showed good cyclic performance. The short reaction times of just 10?min show the basis for an efficient and time-saving synthesis of nanosized LiMn0.7Fe0.3PO4.  相似文献   

11.
A new lithium cobalt metaphosphate, LiCo(PO3)3, is reported for the first time, which was discovered during the exploratory synthesis in Li-Co-P-O system by solid state reaction. The structure has been refined by powder X-ray Rietveld refinement method (P212121, a = 8.5398(2) Å, b = 8.6326(2) Å and c = 8.3520(2) Å, Z = 4, Rp = 13.6%, Rwp = 19.4%, Rexp = 17.7%, S = 1.11, χ2 = 1.23). It is isostructural with LiM(PO3)3 (M = Fe, Cu). It contains (PO3)1− chains with the Co atoms localized in the octahedral sites, bridging four neighboring chains. The magnetic susceptibility measurement showed a typical paramagnetic behavior of high spin of Co2+, following the Curie-Weiss law in the temperature range of 5-300 K. Unlike the olivine type lithium cobalt phosphate, LiCoPO4, cyclic voltammetry of LiCo(PO3)3 assembled in the coin-type cell showed no electrochemical activity in the voltage region of 1-5 V versus Li/Li+.  相似文献   

12.
The effect of Ti4+ ion on the formation of magnetite, which were prepared by solid-state route reaction method, were studied by resistivity, Raman and 57Fe Mössbauer spectrometry. Resistivity measured in the range of 10 < T < 300 K for Ti4+ magnetite Fe3−xTixO4 exhibit first order phase transformations at the Verwey transition Tv for Fe3O4, Fe2.98Ti0.02O4 and Fe2.97Ti0.03O4 at 123 K, 121 K and 118 K, respectively. No first order phase transition was observed for Fe2.9Ti0.1O4 and small polaron model retraces the semiconducting resistivity behavior with activation energy of about 72 meV. The changes in Raman spectra as a function of doping show that the changes are gradual for samples with higher Ti doping. The Raman active mode for Fe2.9Ti0.1O4 at ≅634.4 cm−1 is shifted as compared to parent Fe3O4 at ≅670 cm−1, inferring that Mn2+ ions are located mostly on the octahedral sites. 57Fe Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Ti4+ ions are located mostly on the octahedral sites of the Fe3−xTixO4 spinel structure.  相似文献   

13.
LiFe1−x Mn x PO4 solid solutions in the whole concentration range (0 ≤ x ≤ 1) are obtained at 500 °C by a phosphate–formate precursor method. The method is based on the formation of homogeneous lithium–iron–manganese phosphate–formate precursors by freeze-drying of aqueous solutions containing Li(I), Fe(II), Mn(II), phosphate, and formate ions. Thermal treatment of the phosphate–formate precursors at temperatures at 500 °C yields nano-sized LiFe1−x Mn x PO4 coated with carbon. The structure and the morphology of the LiFe1−x Mn x PO4 compositions are studied by XRD, IR spectroscopy, and SEM analysis. The in situ formed carbon is analyzed by Raman spectroscopy. The electrochemical performance of LiFe1−x Mn x PO4 is tested in model lithium cells using a galvanostatic mode. All LiFe1−x Mn x PO4 compositions are characterized with an ordered olivine-type structure with a homogeneous Fe2+ and Mn2+ distribution in the 4c olivine sites. The morphology of LiFe1−x Mn x PO4 consists of plate-like aggregates which are covered by in situ formed carbon. Inside the aggregates nano-sized isometric particles with narrow particles size distribution (between 60 and 100 nm) are visible. The structure of the deposited carbon presents a considerable disordered graphitic phase and does not depend on the Fe-to-Mn ratio. The solid solutions LiFe1−x Mn x PO4 deliver a good reversible capacity due to the Fe2+/Fe3+ and Mn2+/Mn3+ redox-couples at 3.5 and 4.1 V, respectively.  相似文献   

14.
Nanocrystalline LiMn2O4 powders have been synthesized by combustion process in a single step using a novel fuel, l-alanine. Thermogravimetric analysis and differential thermal analysis of the gel indicate a sharp combustion at a temperature as low as 149 °C. Quantitative phase analysis of X-ray diffraction data shows about 97% of phase purity in the as-synthesized powder, which on further calcination at 700 °C becomes single phase LiMn2O4. High Brunauer, Emmett, and Teller surface area values obtained for ash (53 m2/g) and calcined powder (23 m2/g) indicate the ultrafine nature of the powder. Average crystallite size is found to be ∼60-70 nm from X-ray diffraction analysis and transmission electron microscopy. Fourier transformed infra-red spectrum shows two strong bands at 615 and 511 cm−1 originating from asymmetrical stretching of MnO6 octahedra. A nominal composition of Li0.88 Mn2O4 is calculated from the inductive coupled plasma analysis. From UV-vis spectroscopy, an optical band gap of 1.43 eV is estimated which is assigned to a transition between t2g and eg bands of Mn 3d. Electrochemical charge-discharge profiles show typical LiMn2O4 behavior with a specific capacity of 76 mAh/g.  相似文献   

15.
Quaternary spinel oxide LiMn1.825Cr0.175O4 powder was synthesized by using an ultrasonic spray pyrolysis method, without additional annealing. The crystal structure of the as-prepared powder was revealed by X-ray powder diffraction and identified as a single spinel phase with Fd3m space group. The powders had a spherical morphology with extremely smooth surface appearance and densely congested interior structure. Transmission electron microscopy confirmed that the particle consisted by the cohesion of the primary particles. Magnetic measurements performed in DC field in both zero-field-cooled and field-cooled regimes, as well as AC susceptibility experiments, show that system undergoes spin-glass transition at the freezing temperature Tf = 20 K. The value of the effective magnetic moment μeff = 4.34 μB obtained from the Curie-Weiss fit in the high temperature region confirms the substitution of Mn3+ ions with Cr3+ ions.  相似文献   

16.
Li3 − xFe2 − xTix(PO4)3/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li3Fe2(PO4)3/C (x = 0) and Li2.8Fe1.8Ti0.2(PO4)3/C (x = 0.2) possess two plateau potentials of Fe3+/Fe2+ couple (around 2.8 V and 2.7 V vs. Li+/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li2.8Fe1.8Ti0.2(PO4)3/C has higher reversibility and better capacity retention than that of the undoped Li3Fe2(PO4)3/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.  相似文献   

17.
A new iron(III) phosphate Na3Fe3(PO4)4 has been synthesized and characterized. It decomposes before melting at 860°C into FePO4 and Na3Fe2(PO4)3. The structure of the compound was determined by single-crystal X-ray diffraction. The unit cell is monoclinic with the following parameters: a=19.601(8) Å, b=6.387(1) Å, c=10.575(6) Å and β=91.81(4)°; Z=4; space group: C2/c. Na3Fe3(PO4)4 exhibits a layered structure involving corner-linkage between FeO6 octahedra, and corner- and edge-sharing between FeO6 octahedra and PO4 tetrahedra. The Na+ cations occupying the interlayer space are six- and seven-fold coordinated by oxygen atoms. The relationship between the structure of Na3Fe3(PO4)4 and the previous reported hydrate K3Fe3(PO4)4·H2O will be discussed.  相似文献   

18.
MgAl2O4:Mn2+ hexagonal nanoplates have been synthesized via a simple two-step method. The nanoplates have uniform hexagonal morphology with an average edge length of 1 μm and thickness of 30 nm. X-ray diffraction and various microscopic techniques indicate that MgAl2O4:Mn2+ nanoplates are single-crystal with multilayered morphology. The formation mechanism has also been discussed. Photoluminescence (PL) spectrum of the MgAl2O4:Mn2+ nanoplate shows a broad green emission band centered at 568 nm, which is assigned to the 4T1 → 6A1 transition of Mn2+ ion. The MgAl2O4:Mn2+ nanoplate is a promising candidate for efficient nanoscale optical material.  相似文献   

19.
The spinel compound LiCr0.1Ni0.4Mn1.5O4 was synthesized by a solid reaction method and a sol-gel method using citric acid as chelating agent. The pure phase LiCr0.1Ni0.4Mn1.5O4 was obtained by the wet method. The electrochemical performances of the pure phase sample were measured at different current rates. There were three voltage plateaus at about 4.9, 4.7 and 4.0 V in the charge-discharge curves, which were attributed to the oxidation/reduction of chromium, nickel and manganese respectively. In the range of 3.5-5.0 V, its first discharge capacity was 143, 118 and 111 mAh/g corresponding to current densities of 1.0, 4.0 and 5.0 mA/cm2, respectively. After 50 cycles, the capacity retention remained well at the current densities of 1.0, 4.0 and 5.0 mA/cm2. The electrochemical performances of pure phase LiCr0.1Ni0.4Mn1.5O4 at 55 °C was also measured, and the results were discussed.  相似文献   

20.
LiMn2O4 spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt.% of La2O3 by polymeric process, followed by calcinations at 850 °C for 6 h in air. The surface coated LiMn2O4 cathode materials were physically characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and XPS. XRD patterns of La2O3-coated LiMn2O4 revealed that the coating did not affect the crystal structure and space group Fd3m of the cathode materials, compared to the uncoated LiMn2O4. The surface morphology and particle agglomeration were investigated using scanning electron microscopy and the TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 100 nm. XPS data illustrated that the La2O3 was completely coated over the surface of the LiMn2O4 core cathode materials. The galvanostatic charge and discharge of the uncoated and La2O3-coated LiMn2O4 cathode materials were carried out in the potential range of 3.0 and 4.5 V at 30 °C and 60 °C. Among them, 2.0 wt.% of La2O3-coated spinel LiMn2O4 cathode has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries.  相似文献   

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