Upconversion Luminescence Properties and Mechanism of Er^(3+) Doped Ba_(0.65)Sr_(0.35)TiO_3 Ferroelectric Oxide Nanocrystals

Ba0.65Sr0.35TiO3(BST) nanocrystals doped with different concentrations of Er3+ ion were fabricated using sol-gel method. The structure and morphology of these BST nanocrystals were studied using X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM). The X-ray diffraction patterns of all the nanocrystals prepared in the study correspond to polycrystalline perovskite BST structure. The blue and green upconversion luminescence properties of Er3+ doped BST nanocrystals were investigated under excitation by a 785-nm laser. The upconversion emission bands centered at 407, 523, and 547 nm can be attributed to 2H9/2, 4I15/2, 2H11/2, 4I15/2, and 4S3/2, 4I15/2 transitions of Er3+ ion, respectively. The upconversion mechanism was studied in detail, based on the laser power dependence of the upconverted emissions. In addition, we examined the dependence of the intensity of green upconverted luminescence on the doping concentration of Er3+ ions, and discussed the mechanism underlying the process.

Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO_3 bulk:Effects of annealing temperatures

Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W–O–W stretching, W–O–W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450–800 nm are very different with changing annealing temperatures from the room temperature to 400℃. After annealing at 400℃, the film becomes almost transparent. Increasing annealing time at 400℃ can lead to a small blue shift of the optical gap of the film.

Characterization of low-resistance ohmic contacts to heavily carbon-doped n-type InGaAsBi films treated by rapid thermal annealing

Carbon-doped In Ga As Bi films on In P:Fe(100)substrates have been grown by gas source molecular beam epitaxy(GSMBE).The electrical properties and non-alloyed Ti/Pt/Au contact resistance of n-type carbon-doped In Ga As Bi films were characterized by Van der Pauw-Hall measurement and transmission line method(TLM)with and without rapid thermal annealing(RTA).It was found that the specific contact resistance decreases gradually with the increase of carrier concentration.The electron concentration exhibits a sharp increase,and the specific contact resistance shows a noticeable reduction after RTA.With RTA,the In Ga As Bi film grown under CBr4 supply pressure of 0.18 Torr exhibited a high electron concentration of 1.6×10^(21) cm^(-3) and achieved an ultra-low specific contact resistance of 1×10^(-8)Ω·cm^(2),revealing that contact resistance depends greatly on the tunneling effect.

Effects of Strain Channel on Electron Irradiation Tolerance of InP-based HEMT Structures

The introduction of strain In_(x)Ga_(1-x)As channel with high In content increases the confinement of the two-dimensional electron gas(2DEG)and further improves the high-frequency performance of InGaAs/InAlAs/InP HEMTs.The effect of In_(x)Ga_(1-x)As channel with different In contents on electron irradiation tolerance of InP-based HEMT structures in terms of 2DEG mobility and density has been investigated.The experiment results show that,after the same high electron irradiation dose,the 2DEG mobility and density in InP-based HEMT structures with strain In_(x)Ga_(1-x)As(x>0.53)channel decrease more dramatically than that without strain In_(0.53)Ga_(0.47)As channel.Moreover,the degradation of 2DEG mobility and density becomes more severe as the increase of In content and strain in the In_(x)Ga_(1-x)As channel.The research results can provide some suggestions for the design of radiation-resistant InP-based HEMTs.

Engineered interface of three-dimensional coralliform NiS/FeS_(2)heterostructures for robust electrocatalytic water cleavage

Heterojunction structures improve the intrinsic activity of electrocatalysts by enhancing the charge transfer between the catalyst and the electrode.In this paper,the NiS/FeS_(2)heterostructured electrocatalyst is fabricated by a simple sulfidation method using an interface engineering strategy to adjust the surface electron density of the electrocatalyst.As expected,NiS/FeS_(2)electrocatalyst exhibits superior activity and durable oxygen evolution reaction(OER)stability,requiring only a low overpotential of 183 mV to achieve a current density of 10 mA·cm^(−2)and can be stable for more than 80 h,superior to NiS,FeS_(2)electrocatalyst individually,and precious RuO_(2).Notably,NiS/FeS_(2)is also a good bifunctional electrocatalyst with good overall water splitting performance,and it only requires a voltage 1.56 V to obtain a current density of 10 mA·cm^(−2)for more than 12 h.Remarkably,the NiS/FeS_(2)hybridization facilitates the formation of coral-like structures,increasing the electrochemical surface area(ECSA)and enhancing the charge transfer efficiency,thus leading to excellent electrocatalytic performance.This work proposes a constructive strategy for designing efficient electrocatalysts based on interface engineering,and lays a foundation for designing a new class of electrocatalysts.

Computational studies on magnetism and ferroelectricity

Magnetics,ferroelectrics,and multiferroics have attracted great attentions because they are not only extremely im-portant for investigating fundamental physics,but also have important applications in information technology.Here,recent computational studies on magnetism and ferroelectricity are reviewed.We first give a brief introduction to magnets,fer-roelectrics,and multiferroics.Then,theoretical models and corresponding computational methods for investigating these materials are presented.In particular,a new method for computing the linear magnetoelectric coupling tensor without applying an external field in the first principle calculations is proposed for the first time.The functionalities of our home-made Property Analysis and Simulation Package for materials(PASP)and its applications in the field of magnetism and ferroelectricity are discussed.Finally,we summarize this review and give a perspective on possible directions of future computational studies on magnetism and ferroelectricity.

Self-supported porous copper oxide nanosheet arrays for efficient and selective electrochemical conversion of nitrate ions to nitrogen gas

Electrochemical techniques have shown advantages for the removal of low-concentration nitrate.Here,copper oxide nanosheets were grown on self-supporting nickel foam(NF)to prepare electrodes(CuO/NF),which realized the rapid and highly selective conversion of nitrate pollutants in sewage into nontoxic and harmless N_(2).The CuO/NF afforded 100%NO_(3)^(-)removal within 100 min and 99.53%selectivity for N_(2)at-50 mA without producing a lot of by-products(NO_(2)-,NH_(4)^(+),and N_(2)H_(4)).Furthermore,81.8%of NO_(3)^(-)was removed under the given conditions after six experimental repetitions.These results suggest that the cat-alyst has excellent electrochemical stability.The performance of CuO/NF for the electrocatalytic removal of NO_(3)^(-)in simulated wastewater(which contained Cl^(-) and SO_(4)^(2-))was almost unaffected.Because of the high efficiency,high stability,and low cost of CuO/NF,this catalyst is practical for the removal of nitrate for wastewater purification.

One-pot synthesis of Pd-Au-alloy-nanoparticle-decorated graphene oxide functionalized with dodecahydrododecaborate cluster for rapid and complete reduction of 4-nitrophenol at room temperature

The treatment of nitroaromatics in wastewater is a significant issue that must be addressed because of their high cytotoxicity.The catalytic reduction of 4-nitrophenol(4-NP)to the widely used 4-aminophenol(4-AP)is an excellent method for 4-NP removal.However,performing this reaction is difficult.In this study,two-dimensional(2D)graphene oxide(GO)with oxygen-containing surface groups was used as a substrate for the in situ anchoring ofPdAu alloy nanocrystals.

Recent advances in iron-based sulfides electrocatalysts for oxygen and hydrogen evolution reaction

Increasing environmental pollution and shortage of conventional fossil fuels have made it urgent to develop renewable and clean energy sources. Electrocatalytic water splitting, with its abundant raw materials, simple process, and zero carbon emission, is considered one of the most promising processes for producing carbon-neutral hydrogen which has excellent energy conversion efficiency and high gravimetric energy density. Among them, oxygen evolution reaction (OER) electrocatalysts and hydrogen evolution reaction (HER) electrocatalysts are critical to decreasing the intrinsic reaction energy barrier and boosting the hydrogen evolution efficiency. Therefore, it is imperative to develop and design low-cost, highly active, and stable OER and HER electrocatalysts to lower the overpotential and drive the electrocatalytic reactions. Transition metal sulfides, especially iron-based sulfides, have attracted extensive exploration by researchers as a result of its high abundance in the Earth's crust and near-metallic conductivity. Consequently, in this review, we systematically and comprehensively summarize the progress in the application of iron-based sulfides and their composites as OER and HER electrocatalysts in electrocatalysis. Detailed descriptions and illustrations of the special relationships among their composition, structure, and electrocatalytic performance are presented. Finally, this review points out the challenges and future prospects of iron-based sulfides in practical applications for designing and fabricating more promising iron-based sulfide OER and HER electrocatalysts. We believe that iron-based sulfide materials will have a wide range of application prospects as OER and HER electrocatalysts in the future.

ZnGa_(2)S_(4):an infrared nonlinear optical material with large second-harmonic generation response and wide band gap

High-performance nonlinear optical(NLO)crystals are crucial devices to convert wavelength of solid-state lasers.Chalcogenides play an indispensable role in the research of infrared NLO materials.In this work,ternary chalcogenide ZnGa_(2)S_(4) with defect diamond-like structure was screened out and synthesized by chemical vapor transport method.

Recovering Quadruple-cation Perovskite Films from Water Caused Permanent Degradations

To promote the stability and efficiency,quadruple-cation perovskite system(blending of MA,FA,Cs,I,Br,etc)was introduced to substitute the traditional MAPbI3 perovskite.Perovskite films degraded by water can be recovered by a simple method.The PbI2 residues decomposed from perovskite were transformed into perovskite again,which gave rise to remarkably boosted optical properties,drastically improved film morphology and largely suppressed pinholes.The efficiency of the repairing method was testified by fieldemission scanning electron microscopy,atomic force microscopy,X-ray photoelectron spectroscopy,and so on.The power conversion efficiency of fixed perovskite solar cells improved from around 3%to 15.78%(0.16 cm^2,mask area),and 12.56%at area of 1 cm^2,which prove that this method is very effective.

Groups-dependent phosphines as the organic redox for point defects elimination in hybrid perovskite solar cells

Lead(Pb)^(0) and iodine(I)^(0) point defects generated during perovskite solar cell(PSC)fabrication and photoconversion form deep band energy levels as the carriers’recombination centers.These defects not only deteriorate device efficiency,but also facilitate chemical degradation with ion migration,resulting in restricted device lifetime.Herein,we present a novel type of phosphines as the point defects stabilizer for hybrid perovskite solar cells with enhanced performances.Three phosphines with varied side groups of tributyl,trioctyl and triphenyl are exampled as the dopants in perovskite films.The group dependent redox properties were observed in the perovskite film,dependent on their molecular weights and steric hinderances of phosphines.The partially oxidized tributyl phosphine(TBUP)with additional tributyl phosphine oxides(TBPO)is efficient in reduction of lead(Pb)^(0) and iodine(I)^(0) concentrations during the device fabrication and operation.The device with TBUP-TBPO pair showed enhanced power conversion efficiency(PCE)to 20.48% and maintain 91.7% of their initial PCEs after 500 h at 65℃ thermal annealing.Thus,this work presents an efficient route of utilize the phosphine species to reduce point defects in the perovskite film,which promoting further development of novel phosphorous additives with defects stabilization,interface passivation and encapsulation for low-cost solution processed PSCs.

Aqueous Sn-S Complex Derived Electron Selective Layer for Perovskite Solar Cells

A novel aqueous Sn-S complex solution was applied as precursor to fabricate SnO2 electron selective layers (ESLs) for the hybrid perovskite solar cells (PSCs).The tin and sulfur powder were directly dissolved in a (NH4)2S water solution to form Sn-S precursor.After depositon and annealing,the SnO2 film was formed,presenting as a low cost and enviromental friendly method for preparation of ESL.The films showed excellent transmittance at visible wavelength range.Moreover,the method exhibited high compatibility for doping using Cu,Cd,Li,and Zn elements.Zn doping (0.05 M) in the as-prepared SnO2 ESL significantly improved perovskite solar cells (PSCs) performance.The highest PCE of 13.17% was achived with 15% enhancement compared to that of undoped SnO2 ESL samples.TiCl4 modifications on SnO2 film improved photovoltaic performance to 14.45%,but resulted in the poor long-term stability,around 80% more degredation than that of PSCs based on Zn-doped SnO2 films.

First-principles calculations of stability of graphene-like BC_(3) monolayer and its high-performance potassium storage

With increasing demand for renewable energy,graphene-like BC_(3) monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently.However,its structural stability,potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet.In this work,phonon spectra,AIMD simulations and elastic constants of graphene-like BC_(3) monolayer are investigated.Our results show that graphene-like BC_(3) monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653 mAh/g with the corresponding open circuit voltages 0.66 V.Due to potassium atom can be effectively adsorbed at the most energetically favorable h-CC site with obvious charge transfer,making adsorbed graphene-like BC_(3) monolayer change from semiconductor to metal which is really good for electrode utilization.Moreover,the migrations potassium atom on the graphene-like BC_(3) monolayer is rather fast with the diffusion barriers as low as 0.12 eV,comparing lithium atom with a relatively large diffusion barrier of 0.46 eV.Additionally,the tensile strains applied on the graphene-like BC3 monolayer have marginal effect on the adsorption and diffusion performances of lithium,sodium and potassium atoms.

Synthesis and Properties of Novel Polymers Based on PD Electron-withdrawing Unit

In this article, we designed and synthesized a series of 5-(2,6-dimethyl-4H-pyran-4-ylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H, 5H)-dione(PD) unit based polymers(PFTDT, CZTDT, PHTDT and THTDT) for the first time. In these polymers, fluorene, 2,7-carbazole, phenothiazine and thiophene are employed as electron-donating groups and PD as electron-withdrawing group. TGA measurements demonstrated that these polymers possess good thermal stability(all above 377 °C). Very broad absorption spectrum was also obtained from the polymer THTDT(300?850 nm). CV characterization found that these polymers owned low highest occupied molecular orbital(HOMO) energy levels(?5.39 e V for THTDT, ?5.49 e V for CZTDT and ?5.78 e V for PFTDT) except for PHTDT(?5.17 e V). The geometry and electronic properties of PFTDT, CZTDT, PHTDT and THTDT were investigated by means of theoretical calculation. All the above advantages demonstrate that PD based polymers could be candidates for electronic devices.

Sol-gel combustion synthesis and characterization of CoCr2O4 ceramic powder used as color solar absorber pigment

A facile citric acid assisted sol-gel combustion method was performed to synthesize cobalt chromite(CoCr2O4)ceramic pigment.The effect of the annealing temperature on structure,morphologies,and optical properties of the prepared CoCr2O4 pigments were systematically studied by thermogravimetry,differential thermal analysis,X-ray diffraction(XRD)and field emission scanning electron microscope(FESEM).The results show that CoCr2O4 spinel crystal was achieved after heat treatment of the as-burnt powder at a relatively low temperature(400°C)and the average crystallite size of the CoCr2O4 pigment increased with the annealing temperature.Furthermore,on the CIE parameters of CoCr2O4 pigment,a*and b*values became much more negative with the annealing temperature due to much more Co^2+ions located in tetrahedral sites and much more Cr^3+ions located in octahedral sites.Finally,the measured solar absorptance indicates that this ceramic pigment is expected to fabricate the color paint coating for solar absorber application.

Two-dimensional blue-phase CX(X=S,Se)monolayers with high carrier mobility and tunable photocatalytic water splitting capability

Photocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the ene rgy and environmental issues.Recently,two-dimensional(2 D)materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance.In this work,blue-phase monolayer carbon monochalcogenides(CX,X=S,Se)are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory.After confirming the great dynamical,thermal,and mechanical stability of CX monolayers,we observe that they possess moderate band gaps(2.41 eV for CS and 2.46 eV for CSe)and high carrier mobility(3.23×10^(4)cm^(2)V^(^(-1))s^(-1)for CS and 4.27×10^(3)cm^(2)V^(-1)s^(-1)for CSe),comparable to those of many recently reported 2 D photocatalysts.Moreover,these two monolayer materials are found to have large intrinsic dipole(0.43 D for CS and 0.51 D for CSe),thus the build-in internal electric field can be selfintroduced,which can effectively drive the separation of photongenerated carriers.More importantly,the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting.Additionally,the effects of external strain on the electronic,optical and photocatalytic properties of CX monolayers are also evaluated.These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.

Selective conformer detection of short-lived base pair tautomers: A computational study of the unusual guanine-cytosine pairs using ultrafast resonance Raman spectroscopy

Base pair mismatch has been regarded as the main source of DNA point mutations, where minor shortlived tautomers were usually involved. However, the detection and characterization of these unnatural species pose challenges to existing techniques. Here, by using systematic structural and ultrafast resonance Raman(RR) spectral analysis for the four possible conformers of guanine-cytosine base pairs, the prominent marker Raman bands were identified. We found that the hydrogen bonding vibrational region from 2300 cm^(-1) to 3700 cm^(-1) is ideal for the identification of these short live species. The marker bands provide direct evidence for the existence of the tautomer species, thus offering an effective strategy to detect the short-lived minor species. Ultrafast resonance Raman spectroscopy would be a powerful tool to provide direct evidence of critical dynamical details of complex systems involving protonation or tautomerization.

N-doped carbon nanotubes supported CoSe_(2) nanoparticles:A highly efficient and stable catalyst for H_(2)O_(2) electrosynthesis in acidic media

Electrocatalytic oxygen reduction reaction(ORR)provides an attractive alternative to anthraquinone process for H_(2)O_(2) synthesis.Rational design of earth-abundant electrocatalysts for H_(2)O_(2) synthesis via a two-electron ORR process in acids is attractive but still:very challenging.In this work,we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe_(2) nanoparticles well dispersed but alter the crystal structure,which in turn improves the overall catalYtic behaviors and thereby renders high O_(2)-to-H_(2)O_(2) conversion efficiency.In 0.1 M HClO_(4),such CoSe_(2)@NCNTs hybrid delivers a high H_(2)O_(2) selectivity of 93.2% and a large H_(2)0_(2) yield rate of 172 ppm·h^(-1) with excellent durability up to 24 h.Moreover,CoSe_(2)@NCNTs performs effectively for organic dye degradation via electro-Fenton process.

Interlayer-decoupled BiOX (X=Cl, Br, and I) sheets for photocatalytic water splitting:a computational study

In this work, we comprehensively study the electronic and photocatalytic properties of single-layer and multilayer bismuth oxyhalides Bi OX(X=Cl, Br, and I) sheets by means of extensive density functional theory, which have been successfully synthesized in the previous experimental studies. Our computational simulations show that single-layer Bi OX sheets possess indirect band gap, suitable band edge alignments, and pronounced optical properties, suggesting that they can be utilized as photocatalysts for splitting H_(2)O into H_(2) and O_(2) from theoretical aspects. In the case of multilayer Bi OX sheets, some primary physical properties determined the photocatalytic performance are rather robust, almost independent of the layer number. According to these calculated results, we are optimistic that Bi OX sheets, especially for single-layer Bi OI, have great chances to be used for photocatalytic water splitting.