ZnS掺Mn的电子结构研究

 用自旋极化的LSD-LMTO（Local-Spin-Density Linear Muffin-Tin-Orbital Method）方法，对ZnS掺入Mn发光中心的电子结构进行了大型超原胞模拟计算。在自洽收敛的条件下，先对纯ZnS调节计算参数（原子球、空球占空比），使计算的带隙E_g=3.23 eV；然后用原子球替代方式自洽计算杂质密度在E_g中的相对位置，模拟计算了在六角结构ZnS中掺入不同浓度的Mn杂质后有关的杂质能级在E_g中的相对位置。计算结果表明：（1）单个缺陷的杂质能级性质与配位场理论结果相符合，直接用杂质态密度来表示；（2）掺入杂质的浓度对杂质能级位置的影响不大，这与实验结果相一致。     

掺杂对液晶磁场弗里德里克斯转变影响的探讨

采用相位延迟法，通过对分别掺入微量卟啉类物质、纤维蛋白质和双偶氮苯沿面排列5CB液晶磁场弗里德里克斯转变的实验和数值计算，从实验和原理上探讨了微量掺杂对沿面排列5CB液晶磁场弗里德里克斯转变的影响.数值计算结果与实验相符，呈现两种转变过程.研究表明，掺杂物的磁学性质不同、分子的形状和大小不同对液晶弗里德里克斯转变和弗里德里克斯转变阈值的影响不同.进一步的掺杂2-benzothiazolethiol-linked porphyrinatozinc(Ⅱ)实验说明了这种情况. 关键词： 液晶 掺杂 弗里德里克斯转变     

LCD高温显示缺划研究及改善

LCD工业仪表、汽车仪表等对高温工作性能要求越来越严格,高温工作缺划现象严重影响产品显示效果。结合LCD应用环节中遇到的实际情况,对高温缺划产生的原因展开了研究。通过理论分析和实验验证,找到了高温缺划产生原因在驱动频率和N-LINE设置、液晶电压、盒内杂质离子三个方面。频率和N-LINE设置可以减少直流分量电场的作用,液晶电压可以减少强极性分子,盒内杂质离子少可以减少离子聚集。实验结果表明产品可以解决70℃工作500 h高温缺划现象。参数调整优化有效改善了高温缺划现象,通过改善提高了产品品质,取得了很好的经济效益。     

液晶磁致旋光的研究

利用矩阵方法分析了液晶的旋光效应，导出了液晶旋光的矩阵表示. 利用JG-3型连续可调谐磁场仪搭建实验装置，红外1350 nm激光器做光源，测量了偏振光通过磁场作用下BL-009型向列相液晶的旋光角，详细分析了磁场对液晶旋光性能的影响. 通过实验测试，对液晶的阈值磁场强度进行了讨论，同时对实验结果进行了理论上的分析，得出了液晶旋光角随磁场与液晶盒表面夹角而变化的结论，验证了液晶分子轴的旋转方向与磁场的方向无关，这为更好的研究液晶的特性以及液晶器件的设计具有重要的参考价值. 关键词： 液晶 矩阵 磁致旋光     

强激光条件下5CB液晶中的激光诱导衍射环现象

强激光经5CB液晶传播时会产生非线性自相位调制现象,利用532 nm和1 064 nmCW激光研究了强激光条件下5CB液晶中的激光诱导衍射环现象,并对强激光在5CB液晶中产生自相位调制的现象和机理进行了讨论.当532 nm激光和1 064 nm激光功率密度分别大于10 kW/cm2和300 W/cm2时,接收白屏上有较明显的衍射环现象|当激光分别持续作用数十毫秒和数百毫秒量级时间时,接收屏上的衍射环现象消失.分别利用基尔霍夫衍射积分公式的菲涅耳近似和夫朗和费近似形式对5CB中激光自相位调制和激光诱导衍射环进行了数值模拟,数值结果与实验结果符合的较好.基于热传导理论定性分析了5CB液晶在不同波长和入射条件下的三阶非线性系数.结果表明：在强激光入射条件下,热效应是自相位调制的主要原因,这种三阶非线性系数除了与液晶的吸收系数和作用时间相关,还与激光作用面积甚至激光诱导指向矢转动过程相关.     

三模共振光学参变振荡腔中热效应与热自锁定的实验研究

通过在压电陶瓷上加不同扫描速度的三角波电压,对光学参变振荡腔进行腔长扫描,发现内腔非线性晶体的热效应会严重影响共振峰值功率,从而可能用以建立光学参变振荡腔频率的热自锁定,对热效应进行了细致的实验观察并对实验现象作了合理的分析。     

共轭高聚物链中极化子生成的掺杂效应

在紧束缚近似下,用绝热动力学演化的方法研究了共轭高聚物链中低浓度掺杂对极化子生成位置的影响.研究发现,掺入杂质与注入电子的先后次序不同,极化子生成的位置会有很大差别,先注入电子后掺入杂质的情况下,在链端自由区与过渡区,极化子生成位置受杂质影响较小;而先杂质后电子的次序下,极化子的生成位置明显受到杂质的控制.该研究表明共轭高聚物链中极化子的生成位置可通过调节掺杂与电荷注入的次序加以控制,从而可达到间接改变载流子迁移率的目的.     

共轭高聚物链中极化子生成的掺杂效应

在紧束缚近似下,用绝热动力学演化的方法研究了共轭高聚物链中低浓度掺杂对极化子生成位置的影响。研究发现,掺入杂质与注入电子的先后次序不同,极化子生成的位置会有很大差别,先注入电子后掺入杂质的情况下,在链端自由区与过渡区,极化子生成位置受杂质影响较小;而先杂质后电子的次序下,极化子的生成位置明显受到杂质的控制。该研究表明共轭高聚物链中极化子的生成位置可通过调节掺杂与电荷注入的次序加以控制,从而可达到间接改变载流子迁移率的目的。     

向列相液晶中光学相位共轭技术的研究进展

对向列相液晶中光学相位共轭技术的研究进展进行了介绍,分析总结了向列相液晶中光学相位共轭过程的机理与实验方法,并对向列相液晶中的光学相位共轭技术的应用前景进行了展望。     

基于杂质光伏效应的镍掺杂对砷化镓太阳电池性能的影响

利用杂质光伏效应能够使太阳电池充分利用那些能量小于禁带宽度的太阳光子,从而提高电池的转换效率.为了更好地利用杂质光伏效应提高砷化镓太阳电池的转换效率,本文利用数值方法研究在砷化镓太阳电池中掺入镍杂质以形成杂质光伏太阳电池,分析掺镍对电池的短路电流密度、开路电压以及转换效率的影响;同时,探讨电池的陷光结构对杂质光伏太阳电池器件性能的影响.结果表明:利用杂质光伏效应掺入镍杂质能够增加子带光子的吸收,使得电池转换效率提高3.32%;转换效率的提高在于杂质光伏效应使电池的红外光谱响应得到扩展;另外,拥有良好的陷光结构是取得好的杂质光伏效应的关键.由此得出:在砷化镓太阳电池中掺镍形成杂质光伏太阳电池是一种能够提高砷化镓太阳电池转换效率的新方法.     

Orientation phenomena in nematic liquid crystals under a periodic compressional deformation

The orientation behavior of homogeneous planar layers of nematic liquid crystals with open and closed ends in the field of compressional deformations caused by an acoustic effect is studied. The mechanisms determining the connection of the optical response of a nematic liquid crystal (the variable component of an optical signal and its spectrum) with the acoustic parameters (the oscillation amplitude and frequency, and the amplitude of sound pressure) and the layer thickness are revealed. The factors responsible for the mechanism and modes of acoustooptic conversion are considered. It is demonstrated that, by varying the layer thickness, it is possible to implement different modes of signal conversion. The possibility of designing a new modification of a sound receiver based on a nematic liquid crystal and the specific features of this design are discussed. Its advantages over conventional sound pressure receivers based on nematic liquid crystals are indicated, in particular, the absence of limitation of the frequency of the received signal in the low-frequency range.     

Thermodielectric bistability in dual frequency nematic liquid crystal

We report on a thermodielectric bistability in dual frequency nematic liquid crystals (LCs) caused by the anisotropic nature of dielectric heating and director reorientation in an electric field. The bistability is a result of the positive feedback loop: director reorientation --> anisotropic dielectric heating --> dielectric anisotrophy --> director reorientation. We demonstrate both experimentally and theoretically that two states with different temperature and director orientation, namely, a cold planar state and a hot homeotropic state coexist in a LC cell for a certain frequency and amplitude range of the applied voltage.     

Changes of thermo-morphologic and thermotropic properties of liquid crystals at direct and reverse nematic mesophase ↔ isotropic liquid phase transitions: surface-induced effect

In this work, the effect of thin films on the thermo-morphologic and thermotropic properties of the phase transitions between the nematic mesophase and isotropic liquid has been investigated. Investigations have been carried out for both the heating and cooling processes. The temperature and linear widths of the biphasic regions of the direct and reverse phase transitions in nematic liquid crystals versus thickness of the thin films have been calculated with a high accuracy. The shift of the nematic mesophase–isotropic liquid and the isotropic liquid–nematic mesophase phase transition temperatures to higher temperatures and the enlargement of the temperature and linear widths of the biphasic regions as the effect of surfaces have been found.     

Fluctuations in liquid crystals in the presence of a flexoelectric effect

We examine director fluctuations in nematic liquid crystals in an electric field in the presence of a flexoelectric effect. For the planar and homeotropic orientations we calculate the correlation functions and analyze these functions near the Freedericksz transition and the flexoelectric instability threshold. For both geometries we calculate the angular dependence of the intensity of light scattered by director fluctuations and examine its behavior at electric field strengths close to critical. Zh. éksp. Teor. Fiz. 112, 1675–1693 (November 1997)     

Specific features of structural defects in twisted nematic liquid crystals under conditions of electrohydrodynamic instability

The influence of inhomogeneous boundary conditions (director orientation) on the specific features of the formation and evolution of structural defects in 90·-twisted nematic liquid crystals (twisted structures) is investigated in the regime of electrohydrodynamic instability. It is found that, unlike the domain structure of nematic liquid crystals with a planar orientation, in which defects with topological indices of ±1 are formed under conditions of electrohydrodynamic instability, the domain structure of twisted nematic liquid crystals contains both the above defects and defects with a topological index of 0. It is shown that structural defects with a topological index of 0 are stable and that the existence of these defects is associated with the axial velocity u_a of nematic liquid-crystal flow in the domains.     

The domain structure of a nematic liquid crystal layer in an oscillating poiseuille flow

A spatially periodic structure arising in a nematic liquid crystal layer with planar orientation under the effect of an oscillating Poiseuille flow is described theoretically. The effect is analyzed on the basis of hydrodynamic equations of nematic liquid crystals, from which a self-consistent set of equations for perturbations of hydrodynamic variables is separated. It is demonstrated that the structure type and the threshold parameters of the effect depend on the frequency and the layer thickness through the scaling combination ωh ². The dependence of the configuration of arising distortions on the value of viscosity α₃ is analyzed.     

Planar nematic anchoring on SiO-coated substrates

Summary The nematic planar anchoring is usually explained by using simple elastic models: the surface easy axis corresponds to the surface direction that minimizes the excess of nematic elastic energy. When anisotropic rough substrates are used to align nematic liquid crystals, due to the complex surface morphology, usual elastic models are not directly applicable. This paper presents quantitative topographical data of rough substrates, obtained with oblique SiO evaporation under vacuum for nematic planar anchoring. Experimental data are obtained by means of Atomic Force Microscopy and they are used to demonstrate the self-affine nature of these substrates and to relate the nematic anchoring with the anisotropy of the local fractal properties of the substrate itself. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Study of intrinsic anchoring in nematic liquid crystals based on modified Gruhn-Hess pair potential

A nematic liquid crystal slab composed of N molecular layers is investigated using a simple cubic lattice model, based upon the molecular pair potential which is spatially anisotropic and dependent on elastic constants of liquid crystals. A perfect nematic order is assumed in the theoretical treatment, which means the orientation of the molecular long axis coincides with the director of liquid crystal and the total free energy equals to the total interaction energy. We present a modified Gruhn-Hess model, which is relative to the splay-bend elastic constant K₁₃. Furthermore, we have studied the free nematic interfacial behavior (intrinsic anchoring) by this model in the assumption of the perfect nematic order. We find that the preferred orientation at the free interface and the intrinsic anchoring strength change with the value of modification, and that the director profile can be determined by the competition of the intrinsic anchoring with external forces present in the system. Also we simulate the intrinsic anchoring at different temperatures using Monte Carlo method and the simulation results show that the intrinsic anchoring favors planar alignment and the free interface is more disordered than the bulk.     

Study of the photocurrent in liquid crystal cells exhibiting the photorefractive effect

Photocurrents in liquid crystal cells of different structures were experimentally studied. The results of the study confirm the photorefractive mechanism of the light beam self-action in nematic liquid crystals, which consists in a decrease in the density of surface charges screening an external electric field upon light exposure. The data obtained from photoelectric and optical measurements suggest that the photorefractive effect appears in cells with different orientants and in the absence of orientant. In a planar cell oriented by rubbed polyimide, the crucial role is played by the interface between the liquid crystal and polyimide deposited on the anode.     

Optical multisoliton generation in nematic liquid crystals

The nonlocal nonlinearity stemming from molecular reorientation in nematic liquid crystals supports the formation of multiple solitary waves, following the onset of spatial modulational instability from both wide and focused input beams. We report experimental observations of such phenomena at power levels of hundreds of milliwatts in planar cells with a voltage bias.