Rare Earth Luminescent Materials for White LED Solid State Lighting

Solid-state white LED will be a new generation of energy-saving light source in 21 century. In order to emitting white light, one of important approaches is using luminescence conversion technology with rare earth phosphors, which can be excited by the 460 nm blue light or 400 nm near violet light emitted from the InGaN chip and then emit white light. The rare earths doped phosphors prepared by us such as YAG ： Ce^3＋, Ca1-xSrxS ： Eu^2＋, Ga2S3 ： Eu^2＋, MGa2S4：Eu^2＋ （M = Ca, Sr, Ba）, SrGa2＋xS4＋y ：Eu^2＋,（Ca1 - xSrx ） Se ： Eu^2 ＋ , SrLaGaaS6O ： Eu^2 ＋ , （ M1, M2 ） 10 （PO4）6XE（M1 = Ca, Sr, Ba; Ms = Eu, Mn; X = F, Cl, Br） and NaEu0.92 Sm0.08 （MoO4）5 were reported. They emit blue, green, yellow or red color light. Some white LEDs were made by these phosphors with blue or near violet InGaN chips and their chromaticity coordinate （x, y）, correlated color temperature Tc, and color rendering index Ra are reported.

Characteristics of Sb6Te4/VO2 Multilayer Thin Films for Good Stability and Ultrafast Speed Applied in Phase Change Memory

The Sb6 Te4/VO2 multilayer thin films are prepared by magnetron sputtering and the potential application in phase change memory is investigated in detail. Compared with Sb6 Te4, Sb6 Te4/VO2 multilayer composite thin films have higher phase change temperature and crystallization resistance, indicating better thermal stability and less power consumption. Also, Sb6 Te4/VO2 has a broader energy band of 1.58 eV and better data retention （125℃ for 103/）. The crystallization is suppressed by the multilayer interfaces in Sbf Te4/VO2 thin film with a smaller rms surface roughness for Sbf Te4/VO2 than monolayer Sb4Te6. The picosecond laser technology is applied to study the phase change speed. A short crystallization time of 5.21 ns is realized for the Sb6Te4 （2nm）/VO2 （8nm） thin film. The Sb6 Te4/VO2 multilayer thin film is a potential and competitive phase change material for its good thermal stability and fast phase change speed.

A Simple Time-Resolved Optical Measurement of Diffusion Transport Dynamics of Photoexcited Carriers and Its Demonstration in Intrinsic GaAs Films

We develop a tightly focused pump-probe absorption technique to study diffusion dynamics of photoexcited carriers.It has many advantages including the simple setup and operations,higher detection sensitivity,an analytic descriptive model and fast data samplings.Diffusion dynamics are measured twice,separately using two different-sized probe spots,instead of many time-delayed diffusion profiles of a carrier pocket measured using spatially probe-spot scanning.An analytic model is derived to describe diffusion dynamics.Diffusion dynamics in GaAs are measured to demonstrate the feasibility of this technique.The diffusion coefficient is obtained and agrees well with the reported experimental and theoretical results.

Elemental analysis of copper alloy by high repetition rate LA-SIBS using compact fiber spectrometer

High repetition rate laser-ablation spark-induced breakdown spectroscopy(HRR LA-SIBS) was first used to analyze trace elements in copper alloy samples. The 1064 nm output of an acoustooptically Q-switched Nd:YAG laser operated at a pulse repetition rate of 1 kHz was utilized to ablate copper alloy and to form original plasma, spark-discharge was applied to further breakdown the ablated samples and enhance the emission of the laser-induced plasma. A compact multichannel fiber spectrometer was used to analyze the plasma emission under nongated operation mode. Under the assistance of high repetition rate spark discharge, the plasma emission was able to be improved significantly. The determined limits of the detection of lead and aluminum were 15.5 ppm and 1.9 ppm by HRR LA-SIBS, respectively, which were 11 and 6 folds better than that determined by HRR LIBS under the same laser-ablation condition. This work demonstrates the feasibility of using fiber spectrometer to analyze plasma emission under non-gated operation mode and the possibility of building a portable HRR LA-SIBS system for rapid elemental analysis of copper alloys and other solid samples.

Spin, charge, and orbital orderings in iron-based superconductors

In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity.

Superhydrophobicity of LaMnO3 Coatings with Hierarchical Microstructures

As proposed by Herminghaus, a hierarchical structure could render any surface nonwettable as long as the roughness amplitude at small scales is sufficient to suspend a free liquid surface. Recently we reported that the wettability of La0.7Sr0.3MnO3, an intrinsic hydrophilic oxide, can be tuned from superhydrophilicity to superhydrophobicity by hierarchical microstructures generated by annealing the coatings of La0.7Sr0.3MnO3 powder in nanometric scale at different temperatures. Here we further demonstrate the similar phenomenon observed on LaMaO3 coatings, which conforms THAT the surface geometrical structure is a key factor to determine the wettability.

Thermoluminescence characteristics of NaSr_4(BO_3)_3:Ce^(3+) under β-ray irradiation

The thermoluminescence （TL） properties of Ce3＋ doped NaSr4（BO3）3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4（BO3）3：Ce3＋ phosphor was composed of only one peak. TL kinetic parameters of NaSr4（BO3）3：Ce3＋ were deduced by the peak shape method, the activation energy （E） was 0.590 eV and the frequency factor was 1.008×10^6S^-1. TL dose response was linear in the range of measurement. The 3-dimensional （3D） TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f^05d^1→2F（5/2,7/2） transitions of the Ce3＋ ion. The fading behavior of the NaSr4（BO3）3：Ce3＋ phosphor over a period of 15 d was also studied.

Effect of Samarium on Mn Activated Zinc Borosilicate Storage Glasses

Samarium and manganese co-doped zinc borosilicate state method. The effect of doping samarium on the defect of Mn storage glasses were prepared by high temperature solid activated sample was studied by means of thermoluminescence spectra. It was found that the shallower traps of the sample predominate with the addition of samarium, as a result, the phosphorescence and storage properties of the manganese doped zinc borosilicate glasses were greatly changed.

Thermoluminescence Characteristics of SrB_6O_(10)∶Tb

SrB6010：Tb phosphor was synthesized by high-temperature solid state reaction. The influences of Ce or Li as a co-dopant, Tb concentration and irradiation dose exposure on TL of SrB6010 ： Tb were investigated. Results show that Ce or Li as a co-dopant can not improve the sensitivity of SrB6010：Tb phosphor. TL response depends on Tb concentration and 0.02 is the optimum in the concentration range from 0.01 to 0.10. Using the optimum Tb concentration, we calculated the kinetic parameters of SrB6010：Tb employing the peak shape method, and suggested the phosphor obeying the second order kinetics. TL emission intensity is linearly dependent on the irradiation dose within the dose range of 50 - 200 Gy. The characteristic Tb^3＋ ion emission was observed in TL emission spectrum.

Conductance of metallic nanoribbons with defects

The conductances of two typical metallic graphene nanoribbons with one and two defects are studied using the tight binding model with the surface Green＇s function method. The weak scattering impurities, U - 1 eV, induce a dip in the conductance near the Fermi energy for the narrow zigzag graphene nanoribbons. As the impurity scattering strength increases, the conductance behavior at the Fermi energy becomes more complicated and depends on the impurity location, the AA and AB sites. The impurity effect then becomes weak and vanishes with the increase in the width of the zigzag graphene nanoribbons （150 nm）. For the narrow armchair graphene nanoribbons, the conductance at tile Fermi energy is suppressed by the impurities and becomes zero with the increase in impurity scattering strength, U 〉 100 eV, for two impurities at the AA sites, but becomes constant for the two impurities at the AB sites. As the width of the graphene nanoribbons increases, the impurity effect on the conductance at the Fermi energy depends sensitively on the vacancy location at the AA or AB sites.

Red Long Lasting Phosphorescence of Mn^(2+) Doped Zinc Phosphate Glasses

Mn^2＋ doped ZnO-P2O5 glasses emit red fluorescence, which shows that Mn^2＋ ion doped in zinc phosphate glass is octahedrally coordinated. Moreover, glass samples exhibit bright red long lasting phosphorescence （LLP） when the mole percent of ZnO are more than 60%. After turnoff the irradiation source of UV lamp peaking at 254 nm, the red phosphorescence can be observed for about 6 h in the limit of light perception for naked eyes （0.32 mcd/m^2）. Photoluminescence （PL） spectra, LLP emission spectra and decay curves were detected. Increasing MnO or ZnO content, the phosphorescence intensity can be improved distinctly and the emission wavelength can be also adjusted from 595 nm to 628 nm. According to the structural characteristic of zinc phosphates glasses, we suggest that non-bridge oxygen （NBO） is probably related with the arising of LLE Meantime, the variation of crystal field intensity induced that the LLP emission wavelength red shifts.

Optical Switch Formation in Antimony Super-Resolution Mask Layers Induced by Picosecond Laser Pulses

Sb is a classic material of a super-resolution near field structure （super-RENS） mask layer in which the optical switch formation is often realized by nanosecond laser pulse stimulation. We achieve fast and repeatable optical switching driven by picosecond laser pulses in a proper fluence range on Sb thin films. The optical properties of Sb thin films before and after switching are studied by surface-sensitive micro-area ellipsometry. The change of optical constants after switching is less than 2% in the whole visible range. The Sb mask layer is shown to be very promising for ultrafast super-resolution optical storage applications.

Optical generation of tunable and narrow linewidth radio frequency signal based on mutual locking between integrated semiconductor lasers

An integrated on-chip optical device consisting of two distributed feedback(DFB)lasers and one multimode semiconductor ring laser(SRL)has been numerically investigated.In this optical circuit,the two DFB lasers are injected into the SRL,and with the presence of the four-wave mixing effect and optical feedback,the three semiconductor lasers achieve mutual-locking state.The beating between the output optical spectral lines can generate readily tunable radio frequency signals with high spectral purity.

Microstructure and properties of Si-TaSi_2 eutectic in situ composite for field emission

The Si-TaSi2 eutectic in situ composite for field emission is prepared by electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) crystal growth technique. The directional solidification microstructure and the field emission properties of the Si-TaSi2 eutectic in situ composite prepared by two kinds of crystal growth techniques have been systematically tested and compared. Researches demonstrated that the solidification microstructure of EBFZM can be fined obviously be-cause of the relatively high solidification rate and very high temperature gradient, i.e. both the diameter and inter-rod spacing of the TaSi2 fibers prepared by EBFZM technique were decreased, and the density and the volume fraction of the TaSi2 fibers prepared by EBFZM technique were increased in comparison with that of the TaSi2 fibers prepared by CZ method. Therefore the field emission property of the Si-TaSi2 eutectic in situ composite prepared by EBFZM can be improved greatly, which exhibits better field emission uniformity and straighter F-N curve.

Option Pricing beyond Black-Scholes Model:Quantum Mechanics Approach

Based on the analog between the stochastic dynamics and quantum harmonic oscillator,we propose a market force driving model to generalize the Black-Scholes model in finance market.We give new schemes of option pricing,in which we can take various unexpected market behaviors into account to modify the option pricing.As examples,we present several market forces to analyze their effects on the option pricing.These results provide us two practical applications.One is to be used as a new scheme of option pricing when we can predict some hidden market forces or behaviors emerging.The other implies the existence of some risk premium when some unexpected forces emerge.

Study of intensity-dependent nonlinear optical coefficients of GaP optical crystal at 800 nm by femtosecond pump-probe experiment

The intensity-dependent two-photon absorption and nonlinear refraction coefficients of GaP optical crystal at 800 nm were measured with time-resolved femtosecond pump-probe technique. A nonlinear refraction coefficient of 1.7×10^-17 m^2/W and a two-photon absorption coefficient of 1.5×10^-12 m/W of GaP crystal were obtained at a pump intensity of 3.5 × 10^12 W/m^2. The nonlinear refraction coefficient saturates at 3.5 × 10^12 W/m^2, while the two-photon absorption coefficient keeps linear increase at 6 × 10^12 W/m^2. Furthermore, fifth-order nonlinear refraction of the GaP optical crystal was revealed to occur above pump intensity of 3.5 × 10^12 W/m^2.

Complex energy plane and topological invariant in non-Hermitian system

Non-Hermitian systems as theoretical models of open or dissipative systems exhibit rich novel physical properties and fundamental issues in condensed matter physics.We propose a generalized local–global correspondence between the pseudo-boundary states in the complex energy plane and topological invariants of quantum states.We find that the patterns of the pseudo-boundary states in the complex energy plane mapped to the Brillouin zone are topological invariants against the parameter deformation.We demonstrate this approach by the non-Hermitian Chern insulator model.We give the consistent topological phases obtained from the Chern number and vorticity.We also find some novel topological invariants embedded in the topological phases of the Chern insulator model,which enrich the phase diagram of the non-Hermitian Chern insulators model beyond that predicted by the Chern number and vorticity.We also propose a generalized vorticity and its flipping index to understand physics behind this novel local–global correspondence and discuss the relationships between the local–global correspondence and the Chern number as well as the transformation between the Brillouin zone and the complex energy plane.These novel approaches provide insights to how topological invariants may be obtained from local information as well as the global property of quantum states,which is expected to be applicable in more generic non-Hermitian systems.

[0001]-Oriented InN Nanoleaves and Nanowires: Synthesis,Growth Mechanism and Optical Properties

Novel indium nitride （INN） leaf-like nanosheets and nanowires have been grown on Si substrate by chemical vapor deposition method. The characterization results indicate that the samples are single-crystalline, and the growth direction of the nanowires and nanoleaves is [0001]. The growth mechanism of the InN nanoleaves is following the pattern of vapor-liquid-solid process with a three-step growth process. In addition, the room temperature photoluminescence spectra of two nanostructures show band-to-band emissions around 0.706 eV, where the emission from single nanoleaf is stronger than nanowire, showing potential for applications in optoelectronic devices.

Iron-based superconductors： A new family to find the origin of high Tc superconductivity

Since the discovery of iron-based superconductors in 2008 [1], a new tide of study on high Tc superconductors spreads worldwide quickly. After a few years＇ intensive study, many new compounds of iron-based superconductors have been found and their properties have been disclosed. The great achievement is attributed to the modern experimental techniques, fast developing numerical methods and improved theories during the study of cuprate superconductors or more generally strongly correlated electron systems. For instance, the Fermi surface,

A Global-Optimal Portfolio Theory beyond the R-σModel

Deviations from the efficient market hypothesis allow us to benefit from risk premium in financial markets.We propose a three-pronged(R,σ,H)theory to generalize the(R,σ)model and present the formulation of a three-pronged(R,σ,H)model and its Pareto-optimal solution.We define the local-optimal weights(wR,wσ,WH)that construct the triangle of the quasi-optimal investing subspace and further define the centroid or incenter of the triangle as the optimal investing weights that optimize the mean return,risk premium,and volatility risk.By numerically investigating the Chinese stock market,we demonstrate the validity of this formulation method.The proposed theory provides investors of different styles(conservative or aggressive)an efficient way to design portfolios in financial markets to maximize the mean return while minimizing the volatility risk.