A series of Yb3+/Ho3+/Cr3+ tridoped K2ErF5 microcrystals were synthesized by a facile solvothermal method for the first time. The morphology and upconversion luminescence of the K2ErF5 microcrystals were systematically studied. It was found that the red emission (654 nm) of K2ErF5 microcrystals was selectively enhanced by introducing Ho3+ ion. In order to further improve red luminescence intensity, Cr3+ ion was doped in K2ErF5 microcrystals. The red luminescence intensity reached maximum value when Cr3+ ion concentration was 7 mol%. The mechanisms of the luminescence enhancement were attributed to the synergistic effect among the energy transfer process, the improvement of the microcrystals' crystallinity and the distortion of the local crystal structure with lower symmetry when the Ho3+ and Cr3+ ions were introduced.

利用均相共沉淀法,通过调节前驱体溶液的pH值和尿素浓度,经700℃烧结后合成一系列Y2 O3:Er3+,Yb3+上转换微纳米晶颗粒.用X射线衍射(XRD)、透射电子显微镜(TEM)、Fourier变换红外光谱(FITR)和荧光光谱对样品的物相结构、微观形貌和发光性能进行表征,并分析上转换机理.实验结果表明:前驱体溶液中的pH值对Y2 O3:Er3+,Yb3+粒径影响较大,随着pH值的升高,粒径明显增大,样品在绿色(500～600 nm)和红色(650～700 nm)的上转换荧光强度明显增强,红绿比逐渐减小;尿素浓度对Y2 O3:Er3+,Yb3+纳米颗粒的影响较小.

In this work, the effect of grain size and uniformity of the precursor powder on the electrical property of ceria based electrolytes was investigated. Gadolinia-doped ceria (GDC) samples were treated under different calcination temperatures (600 ;C and 1300 ;C), where their grain size and uniformity were adjusted by varying the ratio of 1300 ;C powder in precursors. The phase composition, morphology and conductivities of mixed GDC samples were characterized by x-ray diffraction (XRD), scanning electron spectroscopy (SEM) and AC impedance, respectively. XRD results revealed that all GDC samples are single cubic fluorite-type structures. As the content of 1300 ;C powder increased, the grain boundary conductivity first dropped markedly to the minimum at the ratio x;=;5% and then basically unchanged, whereas no significant change was observed in bulk conductivity. Our study demonstrated that the ratio of the higher calcination temperature powder in the mixed precursor powder gave rise to the variation of grain size uniformity and the electrical properties of GDC samples.

The pH value and urea concentration of precursor dramatically impact on the particle size, morphology and upconversion luminescence of Y2O3:Yb3+, Er3+ nanophosphors. The lower pH leads to the smaller granula size of the final product, for instance, the crystalline size reduces from similar to 30 nm to similar to 16 nm as pH value varies from 9.3 to 6.7. The intensity of green (21111/2, 453/2 -> 4115/2) and red emission (4F9/2 -> 4115/2) can be effectively and readily tuned by adjusting the pH value and urea content of precursor solution. The sample derived at pH of 6.7 and urea content of 384 mg/mL exhibits the highest red to green ratio, as a result of more surface defects and hydroxyl residues. Besides, the upconversion lifetime investigation further proved that the quenching and nonradiative relaxation from 21111/2 and 453/2 to 4F9/2 caused by the surface defects could be responsible for the relative enhancement of the red emission.

Upconversion NaErF4:Yb,Gd nanocrystals with bright red emissions were prepared via a facile solvothermal method.The crystalline phase,size and the relative intensity of upconversion luminescence can be simultaneously manipulated by adjusting Gd3+ ions contents.The introduction of Gd3+ can effectively promote the cubic to hexagonal phase transformation,size reduction and obviously upconversion luminescence (UCL) intensity improvement of NaErF4:Yb,Gd nanocrystals.XRD,TEM and UCL spectra results reveal that the sample co-doped with 25% Gd3+ ions (mole fraction) of NaErF4:Yb system exhibits the optimized structural and optical properties.Meanwhile,the mechanism involving upconverting photon excitation and energy transfer between Yb3+ ions and Er3+ ions were investigated under the excitation of 980 nm diode laser.

Upconverting NaErF4:Yb3+,Gd3+ nanoparticles (NPs) and nanorods (NRs) with improved red emission have been successfully achieved via a facile hydrothermal route using oleic acid as the assistant surfactant. The crystalline phase, morphology even the size are simultaneously tuned by controlling the reaction temperatures and Gd3+ doping contents. The higher synthesis temperature leads to the morphology evolution from NPs to NRs. The integrated intensity ratio of red to green emissions is much improved for Gd3+ codoping nanostructures. The microstructure characterizations along with the steady and transient spectroscopy are performed to better understand the underlying mechanisms of phase evolution and emission enhancement. For the different states of Er3+, i.e. H-2(11/2) and F-4(9/2), the radiative/non-radiative transition probabilities could be affected by Gd3+ doping in different ways as for NPs and NRs, based on the lifetime and emission intensity data. NaErF4:Yb3+,Gd3+ nanosctructures are expected to have promising applications in multimodal bioimaging for deeper tissue penetration.

We present a first-principles study of electronic structures and magnetic properties in Ni-doped BiFeO3 using the density functional theory + U methods. The BiNixFe1-xO3 (x = 0.125, 0.25, 0.5) multiferroic ceramics represent ferromagnetic properties due to the ferrimagnetic order in Ni-O-Fe, and the magnetic moment rises with increase in Ni doping concentration agreeing well with experimental results. Ni atoms prefer to occupy the diagonal positions in the quasi-plane Ni-O-Fe eight-membered ring. Charge transfer from Bi 6s state to Ni 3d state through O 2p orbital lead to the 2+ oxidation state of Ni, indicating high Neel temperatures of BiNixFe1-xO3, and the electronic state of the system can be described as Bix4+Bi1-x3+Nix2+Fe1-x3+O3. The spin polarization of Bi 6s state and O 2p state near the Fermi level contributes to the total magnetic moment. A spin-polarized acceptor level of about 0.4 eV constituted by Bi 6s state and O 2p state is found, which is responsible for the increase in leakage current of Ni-doped BiFeO3. (C) 2017 Elsevier B.V. All rights reserved.

We calculated the electronic properties of the crystal structures of multiferroic materials BiNixFe1-x O3 (x=0,0.125,0.167,0.25,0.5)using the first-principles based on density functional theory.Calculation results of band structures,Mulliken charges and spin magnetic moments show that partial doping of Fe ions by Ni ions can make the system change from antiferromagnetic order to local ferrimagnetic order, and the total spin magnetic moments increase with the increase of concentration of Ni doping.Ni doping significantly inhibits the magnetic moment of Fe ions at specific sites,this is due to the electronics states of minority spin of Ni-eg orbitals occupied by 50% and the superexchange interaction between Fe and Ni ions.

The intense red up-conversion luminescence in Sc2O3:Yb3+,Er3+ synthesized using a biphasic solvothermal (ST) method was observed upon laser diode pumping at 980 nm. Compared with that found in the bulk sample synthesized using a solid state (SS) reaction at the same sintering temperature (700 °C), the green and red up-conversion luminescence are enhanced by a factor of 19.7 and 23.4, respectively. The relative red intensity of the sample prepared using the ST method at 700 °C for 2 h was enhanced up to 6.6 times compared to that obtained by the SS reaction method at 1600 °C for 6 h. On analyzing the spectral distribution, power dependence and decay curves of Yb3+, we revealed that the red emission of the Er3+:4F9/2 level in Sc2O3:Yb3+,Er3+ was populated via three possible routes, i.e. excited-state absorption (ESA), two-step energy transfer up-conversion (ET) and non-multiphonon relaxation mechanism from the (2H11/2, 4S3/2) via cross-relaxation and energy back transfer (CRB). For the green up-conversion of the Er3+:(2H11/2, 4S3/2) level, a three-photon process described as Yb3+:2F5/2 + Er3+:4F9/2 → Yb3+:2F7/2 + Er3+:2H9/2 occurs in the Sc2O3:Yb3+,Er3+ material. The results indicate that ST-Sc2O3:Yb3+,Er3+ can act as an efficient up-converting red light emitter and ST-Sc2O3 is an appropriate oxide host for up-conversion luminescence.

The effect of Co content and hydrostatic pressure on the electronic structure and absorption properties of wurtzite ZnO has been investigated by first principles calculations. The results reveal that the splitting between the energy levels of Co 3d states increased with pressures, which indicate the enhanced action of the crystalline field. In comparison to pure ZnO, a new peak appears in the low-energy region of the optical absorption spectrum in the system doped with Co and hydrostatic pressure is found to have great influence on the electronic transition of d–d orbital of Co atom in this system.

Using the first-principles calculation, we studied the 180° domain in the ferroelectric material of KNbO 3 and calculated the thickness,energy and barrier height for the coherent motion of the domain wall of both K centered and Nb centered domain walls.Our calculation reveals that the thickness of 180° domain wall is only one to two lattice constants.The K centered domain wall is preferred because its formation energy (7.58 mJ/m2 )is half of that of the Nb centered domain wall (15.1 6 mJ/m2 ).The Nb centered domain wall is unstable and will gradually change to the K centered domain wall.The barrier height for the coherent motion of the domain wall to its neighboring lattice position is 7.58 mJ/m2 .

A new laboratory method has been suggested for synthesizing coesite in the Earth's crust by considering the similar characteristics of local collisions and shearing strength between the earth's plates and the high-energy mechanical ball milling (MBM),combining the high static pressure and high temperature technique，and using the mixtures of α-quartz and graphite as the initial materials, in which Silicon is mixed by the best quality ratio.The lowest pressure and temperature condition for synthesizing coesite is 3.8GPa and 873K.

The scope of this paper is focused on analyzing the chemical degradation of LSCF cathode induced from many sources by GCI technique both from theoretical and experimental sides. As you know, electrochemical reaction occurring in the SOFC cathode is the reduction of oxygen, therefore cathode materials for SOFC have to posses many properties. It is necessary to evaluate the performance and degradation of SOFC cathode since improvement of long-term stability is one of the major issues during SOFC commercialization process. This research is important toward the commercialization of SOFC because efforts are being made to clarify the mechanisms of cell performance degradation and to improve durability effectively.

Improvement of long-term stability is one of the major issues of SOFC. Research efforts are being made to clarify the mechanisms of cell performance degradation and to improve durability effectively. It is necessary to quest for potential degradation sources of all sorts. In this work, influence of sulfur concentration on the performance and durability of SOFC cathode has been studied, and degradation behavior was analyzed for conventional cathode material, (La 0.8 Sr 0.2 )MnO 3 (LSM) by GCI technique.

Using the α-SiO2 and conducted by high-energy mechanical milling as the initial material, we investigated the synthesis of coesite under high temperature and high pressure in the condition of adding a certain amount of hard Fe fillings. The synthetic samples are measured by XRD and Raman, and the results show that a small amount of small-sized coesite can be obtained under 2.5 GPa. Based on these results, it is considered that the forming depth of natural coesite under the earth is likely to be obviously shallower than that of plate exhumation in the traditional subduction-exhumation hypothesis.

Sulfur poisoning effect on the electrochemical performance and long-term durability of SOFC cathode has been investigated for La0.6Sr0.4Co0.2Fe0.8O3(LSCF) by Galvanic Current Interruption (GCI) technology. Cell performance was measured supplying with SO2-containing air to the cathode under a constant current density of 200 mA cm-2. At 800 °C, LSCF cathode showed low tolerance to the sulfur poisoning. SO2tends to react with strontium in LSCF material resulting in the formation of SrSO4in the cathode. This reaction gave rise to microstructural change in the cathode and caused gradual degradation of cell performance.

Electrochemical reaction occurring in the SOFC cathode is the reduction of oxygen, therefore cathode materials for SOFC have to posses many properties. It is necessary to evaluate the performance and degradation of SOFC cathode since improvement of long-term stability is one of the major issues during SOFC commercialization process. The scope of this paper is focused on analyzing the chemical degradation of LSM cathode induced from many sources by GCI technique both from theoretical and experimental sides. This research is important toward the commercialization of SOFC because it could offer valuable information to overview chemical degradations from the SOFC cathode and develop strategy to realize high-durable SOFC.

Cermet anode material NiO-ScSZ and cathode material (La0.8 Sr0.2 )0.98 MnO3 (LSM)were prepared via solid state reaction method. The performance electrolyte-supported single cell of NiO-ScSZ-LSM exibited an output voltage of 0.9 V at 0.2 A described by current-voltage characterized curve.The investigation on the endurance of the single cell indicates that the whole voltage decay is 0.02 V per 1 000 h (at a current density of 0.2 A/cm2 )by electro-chemical measurement.The main resource of it comes from cathodic over-voltage by galvanic current interruption method.

Sulfur poisoning effect on the electrochemical performance and long-term durability of SOFC cathode has been investigated for La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) by Galvanic Current Interruption (GCI) technology. Cell performance was measured supplying with SO 2 -containing air to the cathode under a constant current density of 200 mA cm -2 . At 800 °C, LSCF cathode showed low tolerance to the sulfur poisoning. SO 2 tends to react with strontium in LSCF material resulting in the formation of SrSO 4 in the cathode. This reaction gave rise to microstructural change in the cathode and caused gradual degradation of cell performance.