半导体量子点材料在Nd∶YAG激光辐照下的非线性光学效应(英文)

使用10 ns脉冲调QNd∶YAG激光器Z-scan技术测量了化学合成的无掺杂硫化锌量子点(QDs)以及掺Mn2+硫化锌量子点(QDs)的非线性光学特性,并使用透射电镜技术(TEM)以及X射线衍射法(XRD)表征合成材料的纳米结构。在室温下,分别利用UV-VIS分光光度计和分光荧光计测量了人工合成QDs胶体溶液的线性光学吸收特性以及光致发光的发射特性。样品的吸收特性表明,由于量子限制效应的影响,样品的截止吸收低于硫化锌的截止吸收。样品的光致发光特性显示,掺Mn2+的硫化锌样品显示出明显的光致发光现象,发射峰大约在580 nm;而无掺杂的硫化锌样品在紫外区辐射,发射峰大约在365 nm。对样品的UV-VIS吸收特性分析和TEMXRD分析表明,硫化锌样品的平均粒度(半径)大约为1.2 nm。分析开放光圈(OA)Z-scan技术得到的实验数据,发现在1 064 nm处两种试验样品都会发生四光子吸收(FPA)现象。拟合实验数据得到了两种试验样品的FPA系数以及FPA横截面,结果表明,ZnS QD的FPA横截面的计算值是4.9×10-106cm8.s3.photon-3,比硫化锌的FPA横截面大了5个数量级,而且人工合成的ZnS QD也有光学限制的性质。掺Mn2+离子的样品具有大的FPA横截面和在可见光区有高的发光效率这两个特点,使得该材料适合用于多光子荧光成像。

Structural,optical and antimicrobial properties of pure and Agdoped ZnO nanostructures

In the present work,zinc oxide(ZnO)and silver(Ag)doped ZnO nanostructures are synthesized using a hydrothermal method.Structural quality of the products is attested using X-ray diffraction,which confirms the hexagonal wurtzite struc-ture of pure ZnO and Ag-doped ZnO nanostructures.XRD further confirms the crystallite orientation along the c-axis,(101)plane.The field emission scanning electron microscope study reveals the change in shape of the synthesized ZnO particles from hexagonal nanoparticles to needle-shaped nanostructures for 3 wt%Ag-doped ZnO.The optical band gaps and lattice strain of nanostructures is increased significantly with the increase of doping concentration of Ag in ZnO nanostructure.The anti-microbial activity of synthesized nanostructures has been evaluated against the gram-positive human pathogenic bacteria,Staphylococcus aureus via an agarose gel diffusion test.The maximum value of zone of inhibition(22 mm)is achieved for 3 wt%Ag-doped ZnO nanostructure and it clearly demonstrates the remarkable antibacterial activity.

Synthesis, Characterization and Application of Mg/Al Layered Double Hydroxide for the Degradation of Congo Red in Aqueous Solution

The adsorption properties of layered double hydroxide (Mg/Al-CO3) for the removal of Congo Red (CR) dye from aqueous solution were studied. The layered double hydroxide was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopic (FTIR) and Energy-Dispersive X-ray Spectroscopic (EDX). The effects of various experimental parameters such as contact time, dye concentrations and temperature variation were investigated. The results show that the amount of Congo Red adsorbed increases with increase in temperature but decreases with increase in initial dye concentration and contact time. The data were also fitted to several kinetic models: zero-order kinetic model, first-order kinetic model, second-order kinetic model, pseudo-second-order kinetic model and third-order kinetic model respectively. The adsorption process was best defined by zero-order-kinetic model (R2 = 1). Langmuir, Freundich, Temkin and Dubinin-kaganer-Radushkevich (DPK) adsorption isotherm models were applied to analyze adsorption data with Temkin isotherm being the most applicable to the adsorption process. Thermodynamic parameters e.g. △Go, △So, △Ho and △Hx of the adsorption process were found to be endothermic, spontaneous and feasible.

Synthesis of Barium Nickel Titanium Oxide Stabilized by Citric Acid

Barium nickel titanium oxide particles (Ba2NiTi5O13) were synthesized in the presence of citric acid by using a two step sol-gel method followed by calcination. The addition of citric acid as a stabilizer (mole ratio of 0.5, 1.0, 2.0, 4.0) resulted in the formation of Ba2NiTi5O13 particles with various morphology (i.e. sphere, cube, rod). These various morphology changes were deduced to be caused by citric acid that tends to absorbed on certain dimension of the Ba2NiTi5O13 particles when different concentration of citric acid was added. Besides that, the growth of Ba2NiTi5O13 particles from incorporation of bulky micelles which act as a protective 'shell' that control particle sizes by attaching on the surfaces of particles.

New Decision-Making Technique Based on Hurwicz Criteria for Fuzzy Ranking

Efficient decision-making remains an open challenge in the research community,and many researchers are working to improve accuracy through the use of various computational techniques.In this case,the fuzzification and defuzzification processes can be very useful.Defuzzification is an effective process to get a single number from the output of a fuzzy set.Considering defuzzification as a center point of this research paper,to analyze and understand the effect of different types of vehicles according to their performance.In this paper,the multi-criteria decision-making(MCDM)process under uncertainty and defuzzification is discussed by using the center of the area(COA)or centroidmethod.Further,to find the best solution,Hurwicz criteria are used on the defuzzified data.Anewdecision-making technique is proposed using Hurwicz criteria for triangular and trapezoidal fuzzy numbers.The proposed technique considers all types of decision makers’perspectives such as optimistic,neutral,and pessimistic which is crucial in solving decisionmaking problems.A simple case study is used to demonstrate and discuss the Centroid Method and Hurwicz Criteria for measuring risk attitudes among decision-makers.The significance of the proposed defuzzification method is demonstrated by comparing it to previous defuzzification procedures with its application.

Synthesis and Characterization of Copper Doped Zinc Oxide Thin Films Deposited by RF/DC Sputtering Technique

Undoped and copper(Cu)doped zinc oxide(Zn_(1-x)Cu_(x)O,where x=0-0.065)nano crystal thin films have been deposited on glass substrate via RF/DC reactive co-sputtering technique.The aim of this work is to investigate the crystal structure of ZnO and Cu doped ZnO thin films and also study the effect of Cu doping on optical band gap of ZnO thin films.The identification and confirmation of the crystallinity,film thickness and surface morphology of the nano range thin films are confirmed by using X-ray diffractometer(XRD),scanning electron microscope and atomic force microscope.The XRD peak at a diffractive angle of 34.44°and Miller indices at(002)confirms the ZnO thin films.Crystallite size of undoped ZnO thin films is 27 nm and decreases from 27 nm to 22 nm with increasing the atomic fraction of Cu(x_(Cu))in the ZnO thin films from 0 to 6.5%respectively,which is calculated from XRD(002)peaks.The different bonding information of all deposited films was investigated by Fourier transform infrared spectrometer in the range of wave number between 400 cm^(-1) to 4000 cm^(-1).Optical band gap energy of all deposited thin films was analyzed by ultraviolet visible spectrophotometer,which varies from 3.35 eV to 3.19 eV with the increase of x_(Cu) from 0 to 6.5%respectively.Urbach energy of the deposited thin films increases from 115 meV to 228 meV with the increase of x_(Cu) from 0 to 6.5% respectively.

Equalization of a 10 Gbps IMDD signal by a small silicon photonics time delayed neural network

A small 4-channel time-delayed complex perceptron is used as a silicon photonic neural network(PNN)device to compensate for chromatic dispersion in optical fiber links.The PNN device is experimentally tested with nonreturn-to-zero optical signals at 10 Gbps after propagation through up to 125 km optical fiber link.During the learning phase,a separation-loss function is optimized in order to maximally separate the transmitted levels of 0s from the 1s,which implies an optimization of the bit-error-rate.Testing of the PNN device shows that the excess losses introduced by the PNN device are compensated by the gain in the transmitted signal equalization for a link longer than 100 km.The measured data are reproduced by a model that accounts for the optical link and the PNN device.This allows simulating the network performances for higher data rates,where the device shows improvement with respect to the benchmark both in terms of performance and ease of use.

Endogenous formaldehyde responsive fluorescent probe for bioimaging

Formaldehyde(FA),as the simplest endogenous carbonyl molecule,participates in many biosynthesis and metabolism in living organisms,such as nucleotides and adenosine triphosphate(ATP).FA concentrations are sub-millimolar in the normal healthy body,but can rise significantly in a number of disease pathologies.As a result,detecting endogenous FA is critical for illness diagnosis and rehabilitation therapy monitoring.Recent studies have focused on the FA-responsive turn-on fluorescence probe,which has huge promise in the detection and visualization of FA in living cells and organisms,as well as exceptional use in disease diagnosis and therapeutic monitoring.This review summarizes the fluorescence luminescence mechanism and design concepts of FA fluorescent probes,as well as their recent applications in bioimaging and illness diagnostics.Additionally,this article indicates the present dilemma of FA-responsive fluorescent probe,including selectivity,specificity,and detection mode,which may provide references for the development of FA-responsive fluorescent probes.

2D Ti_(3)C_(2)T_(x)MXene-derived self-assembled 3D TiO_(2)nanoflowers for nonvolatile memory and synaptic learning applications

Two-dimensional(2D)semiconducting materials and transition-metal oxides are promising materials for nonvolatile memory and brain-inspired neuromorphic computing applications.However,it remains chal-lenging to obtain high-quality stacked 2D films with low energy consumptions(or drive currents)be-cause of their high interfacial resistance.In this study,we synthesized 2D Ti_(3)C_(2)T_(x)MXene-derived three-dimensional(3D)TiO_(2)nanoflowers(NFs)as a feasible resistive switching(RS)material with outstanding electronic properties and synaptic learning capabilities.The electrical and optical characteristics of the synthesized material were determined through density functional theory calculations.Electrical measure-ments of the Al/Ti_(3)C_(2)T_(x)-TiO_(2)NF/Pt memory device indicated the occurrence of forming-free switching phenomena with extremely low switching voltages(0.68-0.53 V),stable ON/OFF ratio(2.3×103),and retention greater than 105 s.The Holt-Winters exponential smoothing technique was used for mod-eling and predicting the switching voltages of the RS device.The mechanism underlying the reliable RS was confirmed by observing the dense conductive filaments through conductive atomic force mi-croscopy.Interestingly,the 2D Ti_(3)C_(2)T_(x)MXene-derived 3D TiO_(2)NF-based RS device mimicked the po-tentiation/depression and spike-time-dependent plasticity of a biological synapse.Finally,a convolutional neural network was implemented based on the observed synaptic weights of Al/Ti_(3)C_(2)T_(x)-TiO_(2)NF/Pt for image-edge detection.

Removal and recovery of toxic nanosized Cerium Oxide using eco-friendly Iron Oxide Nanoparticles

Increasing applications of metal oxide nanoparticles and their release in the natural environment is a serious concern due to their toxic nature.Therefore,it is essential to have eco-friendly solutions for the remediation of toxic metal oxides in an aqueous environment.In the present study,eco-friendly Iron Oxide Nanoparticles(IONPs)are synthesized using solvothermal technique and successfully characterized using scanning and transmission electron microscopy(SEM and TEM respectively)and powder X-Ray diffraction(PXRD).These IONPs were further utilized for the remediation of toxic metal oxide nanoparticle,i.e.,Ce02.Sorption experiments were also performed in complex aqueous solutions and real water samples to check its applicability in the natural environment.Reusability study was performed to show cost-effectiveness.Results show that these 200 nm-sized spherical IONPs,as revealed by SEM and TEM analysis,were magnetite(Fe3O4)and contained short-range crystallinity as confirmed from XRD spectra.Sorption experiments show that the composite follows the pseudosecond-order kinetic model.Further k>0.99 for Langmuir sorption isotherm suggests chemisorption as probable removal mechanism with monolayer sorption of Ce02 NPs on IONP.More than 80%recovery of adsorbed Ce02 NPs through ultrasonication and magnetic separation of reaction precipitate confirms reusability of IONPs.Obtained removal%of Ce02 in various synthetic and real water samples was>90%signifying that IONPs are candidate adsorbent for the removal and recovery of toxic metal oxide nanoparticles from contaminated environmental water samples.

Complete crossing of Fano resonances in an optical microcavity via nonlinear tuning

We report on the modeling, simulation, and experimental demonstration of complete mode crossings of Fano resonances within chip-integrated microresonators. The continuous reshaping of resonant line shapes is achieved via nonlinear thermo-optical tuning when the cavity-coupled optical pump is partially absorbed by the material.The locally generated heat then produces a thermal field, which influences the spatially overlapping optical modes, allowing us to alter the relative spectral separation of resonances. Furthermore, we exploit such tunability to continuously probe the coupling between different families of quasi-degenerate modes that exhibit asymmetric Fano interactions. As a particular case, we demonstrate a complete disappearance of one of the modal features in the transmission spectrum as predicted by Fano [Phys. Rev. 124, 1866(1961)]. The phenomenon is modeled as a third-order nonlinearity with a spatial distribution that depends on the stored optical field and thermal diffusion within the resonator. The performed nonlinear numerical simulations are in excellent agreement with the experimental results, which confirm the validity of the developed theory.

Unidirectional reflection from an integrated“taiji”microresonator

We study light transmission and reflection from an integrated microresonator device,formed by a circular microresonator coupled to a bus waveguide,with an embedded S-shaped additional crossover waveguide element that selectively couples counter-propagating modes in a propagation-direction-dependent way.The overall shape of the device resembles a“taiji”symbol,hence its name.While Lorentz reciprocity is preserved in transmission,the peculiar geometry allows us to exploit the non-Hermitian nature of the system to obtain high-contrast unidirectional reflection with negligible reflection for light incident in one direction and a significant reflection in the opposite direction.

Interferometric method to estimate the eigenvalues of a non-Hermitian two-level optical system

Non-Hermitian physics has found a fertile ground in optics. Recently, the study of mode coalescence, i.e., exceptional points, has led to the discovery of intriguing and counterintuitive phenomena. Degeneracies are typically modeled through the coupled mode theory to determine the behavior of eigenstates and eigenvalues. However,the complex nature of the eigenvalues makes their characterization from the response spectrum difficult. Here,we demonstrate that a coherent interferometric excitation allows estimation of both the real and imaginary parts of the eigenvalues. We study the clockwise and counter-clockwise modes in optical microresonators both in the case of Hermitian and non-Hermitian intermodal coupling. We show the conditions by which a resonant doublet,due to the dissipative coupling of counter-propagating modes caused by surface roughness backscattering, merges to a single Lorentzian. This permits us to estimate the optimal quality factor of the microresonator in the absence of modal coupling caused by backscattering. Furthermore, we demonstrate that a taiji microresonator working at an exceptional point shows a degeneracy splitting only in one propagation direction and not in the other. This follows from the strongly non-Hermitian intermodal coupling caused by the inner S-shaped waveguide.

Silicon nanocrystals to enable silicon photonics

Low dimensional silicon, where quantum size effects play significant roles, enables silicon with new photonic functionalities. In this short review, we discuss the way that silicon nanocrystals are produced, their optoelectronic properties and a few device applications. We demonstrate that low dimensional silicon is an optimum material for developing silicon photonics.

Observation of enhanced two-photon absorption in ZnS quantum dots at an ultraviolet wavelength

Two-photon absorption （2PA） in zinc sulphide （ZnS） and Mn2＋-doped ZnS quantum dots is reported by the z-scan technique, with nanosecond pulsed laser radiation at 355 nm. The observed values of the 2PA cross section of all the samples are 105 times larger than that of bulk ZnS.

Fabrication,electrical and photovoltaic characteristics of CuInGeSe4/n-Si diode

The CuInGeSe_4 thin film was deposited onto n-type single crystal silicon wafers by the electron beam deposition technique. The Au/CuInGeSe_4/n-Si/Al heterojunction device has been fabricated. The structure of the CuInGeSe_4 thin film was characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), and energy dispersive X-ray analysis(EDX). The dark current-voltage characteristics of the Au/CuInGeSe_4/n-Si/Al heterojunction diode have been studied at a temperature range of 303-383 K. Also, the photovoltaic properties were examined at different illumination intensities. The capacitance-voltage characteristics of the CuInGeSe_4/n-Si heterojunction were studied at different temperatures in the dark.