Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

半导体纳米材料非线性光学性质的研究进展

半导体纳米材料由于具有重要的理论研究意义和潜在的巨大应用前景而成为当今理论和材料研究的特点，该文综述了半导体纳米材料非线性光学性质的研究进展。     

Optical properties of Quantum Disks: Real density matrix approach

We show how to compute the optical response of a Quantum Disk (QDisk) to an electromagnetic wave as a function of the incident wave polarization, in the energetic region of interband transitions. Both the TM and TE polarization in guided-wave geometry are analyzed. The method uses the microscopic calculation of Quantum Disk eigenfunctions and the macroscopic real density matrix approach to compute the effective QDisk susceptibility, taking into account the valence band structure of the QDisk material and the Coulomb interaction between the electron and the hole. Analytical expressions for the QDisk susceptibility are obtained for a certain model electron — hole potential. Using these expressions, all optical functions can be computed. Results for the absorption coefficient are computed for InAs/GaAs QDisks. Fair agreement with experiments is obtained.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Optical properties of multilayer materials based on silicon and nanosized magnesium silicide crystallites

We have studied the optical properties of silicon with incorporated nanocrystallites of semiconducting magnesium silicide by optical spectroscopy and Raman spectroscopy. We have calculated the optical functions of samples grown with different numbers of layers of incorporated magnesium silicide nanocrystallites. We have determined the contribution of magnesium silicide to the electronic structure of multilayer samples in the photon energy range 1.5–3.0 eV. We have studied the phonon structure of the grown multilayer samples, based on analysis of two-phonon and three-phonon resonances in silicon and Mg₂Si. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 204–209, March–April, 2006.     

Structure distortion,optical and electrical properties of ZnO thin films co-doped with Al and Sb by sol-gel spin coating

ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl 3 to SbCl 3 at 1:2, are prepared by a sol-gel spin-coating method on glass annealed at 550°C for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×10 8 , 3.26×10 8 , 5.23×10 8 , and 6.97×10 8 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm.     

The structural and magnetic powders prepared by properties of barium ferrite the sol-gel method

In this paper,M-type hexagonal barium ferrite powders are synthesized using the sol-gel method.A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 C using thermo-gravimetric analysis and differential scanning calorimetry.The effects of the additives and the cacinating temperature on the magnetic properties are investigated,and the results show that single-phase barium ferrite powders can be formed.After heat-treating at 950 C for 4h with 3 wt% additive,the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g,respectively.     

Optical properties of silver selenium indate films obtained by the method of pulse laser vaporization

The spectra of transmission and reflection are measured in the region of 0.4–2.5 μm on thin silver selenium indate films obtained by means of pulse laser vaporization. The magnitudes of the refractive index and absorption coefficient are calculated. The energies of interband transitions and the values of crystalline and spin-orbit splitting are determined. The experimental results for the AgInSe₂ films agree with the data for bulk crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 512–514, July–August, 2000.     

利用金兹堡-朗道理论研究无序光晶格中超冷玻色系统的相变问题

在冷原子物理中,对无序和温度效应的研究一直是一个非常重要的课题。基于金兹堡-朗道理论,我们从解析上研究了无序和有限温度对光晶格中超冷玻色系统相变的影响。我们的计算结果显示,无序强度的增加会使得系统的Mott绝缘相区域减小;热涨落的存在将进一步破坏Mott绝缘相,同时使得系统中出现了正常流体相。这里的金兹堡-朗道理论在最低阶近似下得到的相界方程与平均场结果一致,原则上很容易将计算结果推广到高阶从而给出超越平均场的结果。     

Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by the Bridgman method

Optical absorption,excitation,and fluorescence were investigated in Eu ion-doped CdWO4 single crystal grown by a modified Bridgman method.The results indicate that Eu2+ and Eu3+ ions coexist in CdWO4 crystal and an energy transfer occurs between these Eu2+ and Eu3+ ions.When the crystal is excited by 266-nm light,the energy corresponding to the 4f65d to 8S7/2 transition of Eu2+ ions results in the excitation of the Eu3+ ions to the 5DJ level.The effect on fluorescence of annealing in oxygen at various temperatures was investigated.The excitation intensity of Eu2+ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K,but it remains at a certain equilibrium level when the annealing temperature is further increased.     

赤潮生消过程中的水体固有光学性质分析

在珠江口海域海洋光学浮标实验中获取一次聚生角毛藻赤潮生消过程的水体光学数据和相应的生化数据.利用该数据,分析了赤潮生消过程中水体光谱吸收和后向散射等光学性质的时间序列变化.研究发现,在赤潮生消过程中,浮游植物色素、非藻类颗粒物以及黄色物质等水体组分吸收变化显著,赤潮爆发期各组分光谱吸收增强并达到最大值,赤潮消亡期各组分...     

Structural and optical properties of WO<Subscript>3</Subscript> electrochromic layers prepared by the sol-gel method

Thin layers of tungsten trioxide have been prepared from an aqueous solution of peroxotungstic acid (PTA) using the sol-gel method. Compositional, structural and optical characteristics of WO₃ coated on indium tin oxide (ITO) conductive glass substrates were studied using X-ray diffractometery (XRD), cyclic voltammetery (CV), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Monoclinic and triclinic crystalline structures for thin film and powdered WO₃ were confirmed by XRD analysis. SEM micrograph of annealed samples revealed micro cracks due to a decrease in density and a contraction of layers. EDX analysis showed that 1∶2 ratio of oxygen and tungsten atoms in the prepared films is obtained at heat treatment temperatures higher than 200 °C. Furthermore, the annealed samples showed very good electrochromic behavior in cyclic voltammetery studies. Refractive index “n” and extinction coefficient “k” values were found to be reduced by increasing the wavelength and decreasing the temperature.     

双折射光纤中三阶色散对孤子脉冲传输的影响

研究了孤子脉冲在双折射光纤零色散点附近的传输特性,应用数值分析方法,讨论了在双折射光纤中,三阶色散对孤子脉冲传输的影响。在输入脉冲两个偏振分量强度相等的情况下,分析发现孤子捕获条件没有变化,但是,脉冲一个偏振分量迅速展宽,另一偏振分量展宽变慢。同时,脉冲的形状、光谱在两个偏振分量中都呈现出不对称性。在一定的条件下,孤子的辐射波主要集中在一个偏振分量中。     

Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by Bridgman method

Optical absorption, excitation, and fluorescence were investigated in Eu ion-doped CdWO₄ single crystal grown by a modified Bridgman method. The results indicate that Eu²⁺ and Eu³⁺ ions coexist in CdWO₄ crystal and an energy transfer occurs between these Eu²⁺ and Eu³⁺ ions. When the crystal is excited by 266-nm light, the energy corresponding to the 4f⁶5d to ⁸S_7/2 transition of Eu²⁺ ions results in the excitation of the Eu³⁺ ions to the ⁵D_J level. The effect on fluorescence of annealing in oxygen at various temperatures was investigated. The excitation intensity of Eu²⁺ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K, but it remains at a certain equilibrium level when the annealing temperature is further increased.     

Optical and transport properties of Cd0.8Zn0.2S:Cu compounds prepared by modified chemical co-precipitation method

Cd_0.8Zn_0.2S bulk compound doped with different concentrations of copper have been prepared by chemical co-precipitation (CCP-I) and modified CCP method (CCP-II). The structural, optical and electrical properties of Cd_0.8Zn_0.2S:Cu compounds grown by these methods have been investigated by using XRD, SEM, EDAX, UV spectroscope and DC electrical conductivity techniques. X-ray diffraction studies on Cd_0.8Zn_0.2S compounds doped with various mole% of copper revealed that they possessed polycrystalline nature with hexagonal structure. SEM micrographs taken on samples grown by CCP-I showed that the crystallites have needle like shape and no such regular shape was observed on CCP-II grown samples and in both of them the crystallite size varied differently with the variation in the concentration of copper. The energy gap of a sample grown by CCP-II, evaluated from optical absorption studies, are more than that of the sample grown by CCP-I. This may be attributed to the variation observed in the crystallite sizes of the respective sample grown by two methods. Further, the electrical conductivity variations in CCP-I and II samples were explained based on E_g value, crystallite size and grain boundary conduction in the samples. The activation energies of both CCP-I and II samples were explained on the basis of the differences in their preparation methods. Finally, it was concluded that the CCP-II method is more suitable to grow Cd_0.8Zn_0.2S:Cu compounds with uniform average crystallite size and energy gap for low doping concentration of Cu (∼4 mole%).     

Intersubband resonant enhancement of the nonlinear optical properties in asymmetric (CdS/ZnSe) based quantum wells

In this work, the linear and nonlinear optical properties are studied theoretically in asymmetric (CdS/ZnSe/BeTe)/(ZnSe/BeTe) quantum wells. The electronic states are calculated using the envelope wave function approximation and the intersubband transition energies are studied as a function of CdS and ZnSe well thicknesses as well as doping concentration. The optimum parameters carrying out the transition energy 0.8 eV (1.55 μm wavelength) are given. Results are presented for the linear, the third order nonlinear optical absorption and the refractive index changes in the studied heterostructure. Results show that the changes in the linear and the third order nonlinear optical absorption as well as refractive index change are as important as the temperature is high, the nonlinear terms must be taken into consideration especially near the resonance.     

Energy level of an electron in a saddle-potential quantum dot under a uniform magnetic field obtained by the invariant eigenoperator method

We show that the recently proposed invariant eigenoperator method can be successfully applied to solving the energy levels of an electron in a saddle-potential quantum dot under a uniform magnetic field. The Landau diamagnetism decreases with the value ω_y² - ω_x² due to the existence of the saddle potential.     

化学溶液法制备的Bi3.25La0.75Ti3O12和Bi3.25Nd0.75Ti3O12薄膜的光学特性

采用化学溶液方法在(111)Pt／Ti/SiO2/Si衬底上制备了Bi3.25La0.75Ti3O12(BLT)和Bi3.25Nd0.75Ti3O12(BNT)薄膜．x射线衍射测试表明，两种薄膜都为单一的层状钙钛矿结构．扫描电子显微镜分析显示，BNT薄膜由大而均匀的棒状晶粒组成，BLT薄膜的组成晶粒则较小．采用紫外一近红外椭圆偏振光谱仪测试了200-100nm波长范围的椭圆偏振光谱，拟合得到薄膜的光学常数(折射率和消光系数)和厚度，确定BLT薄膜的禁带宽度分别为4．30和3．61eV，并采用单电子振子模型分析了薄膜在带间跃迁区的折射率色散关系．     

Effect of RF power and sputtering pressure on the structural and optical properties of TiO2 thin films prepared by RF magnetron sputtering

TiO₂ thin films were deposited onto quartz substrates by RF magnetron sputtering. The samples deposited at various RF powers and sputtering pressures and post annealed at 873 K, were characterized using X-ray diffraction (XRD), micro Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL) spectroscopy. XRD spectrum indicates that the films are amorphous-like in nature. But micro-Raman analysis shows the presence of anatase phase in all the samples. At low sputtering pressure, increase in RF power favors the formation of rutile phase. Presence of oxygen defects, which can contribute to PL emission is evident in the XPS studies. Surface morphology is much affected by changes in sputtering pressure which is evident in the SEM images. A decrease in optical band gap from 3.65 to 3.58 eV is observed with increase in RF power whereas increase in sputtering pressure results in an increase in optical band gap from 3.58 to 3.75 eV. The blue shift of absorption edge in all the samples compared to that of solid anatase is attributed to quantum size effect. The very low value of extinction coefficient in the range 0.0544-0.1049 indicates the excellent optical quality of the samples. PL spectra of the films showed emissions in the UV and visible regions.