稀土氧化物纳米粒子调制聚合物分散液晶电光特性的研究

通过对聚合物分散液晶(PDLC)掺杂稀土氧化物纳米粒子Gd2O3,Eu2O3和Nd2O3,测试可见光范围内PDLC掺杂前后的透射率随驱动电压的变化,进而研究稀土氧化物对PDLC电光特性的调制作用。实验结果表明:掺杂Gd2O3的PDLC样品透射率在驱动电压低于10V时,随驱动电压升高而降低,当驱动电压达到为15V时,样品对光感应出现了弛豫现象,使得其透射率围绕10V时的透射率做微小的上下波动,当驱动电压达到20V时,样品透射率迅速升高,并出现了滤光现象;掺杂Eu2O3的PDLC样品透射率随驱动电压升高而下降,下降的幅度较小;掺杂Nd2O3的PDLC样品透射率随驱动电压的变化不明显。     

电控聚合物分散液晶变焦全息透镜制作

介绍了相位型全息聚合物分散液晶(PDLC)材料全息透镜,在电场作用下液晶微滴折射率逐渐与聚合物折射率匹配,实现透镜电控变焦。研究了微米尺寸和纳米尺寸液晶微滴聚合物分散液晶材料配方特性和微观结构。采用优化纳米尺寸材料配方制作5~6μm聚合物分散液晶盒,采用离轴式平面波和球面波干涉全息写入光路,成功制作电控变焦聚合物分散液晶全息透镜样品。该透镜样品焦距为20 mm,能够正一级衍射放大成像。实现“0”,“1”变焦的驱动电压阈值为60 V。并进一步提出了基于聚合物分散液晶电控变焦元件集成叠加技术实现电控变焦光学成像系统的技术思路。     

纳米银掺杂的高效率全息聚合物分散液晶光栅制备

报道了一种基于掺杂纳米银聚合物分散液晶(PDLC)材料的高衍射率全息电控光栅的制备及特性。通过在原有聚合物分散液晶材料体系中添加适量的纳米银颗粒以制备体全息光栅,实验研究了掺杂不同质量比的纳米银颗粒对全息聚合物分散液晶(H-PDLC)体光栅的衍射效率、驱动阈值电压、响应时间的影响。实验结果表明,通过掺杂纳米银材料,能够优化聚合物和液晶两相分离结构,使聚合物与液晶分离更加彻底,显著提高H-PDLC体光栅的一级衍射效率,同时能改善体光栅的电光特性,缩短响应时间。初步分析表明,由于纳米银颗粒的表面等离子体效应和体系折射率匹配的优化改善了H-PDLC光栅的特性。     

柔性PDLC的实验规律

以制作性能良好的柔性PDLC为目标,从材料的选取、制作过程和电光特性等方面进行了研究。电极和聚合物选用柔性的ITO导电膜和紫外固化光学胶NOA65,液晶为向列相液晶混合物P0616A,采用紫外光聚合法,制作出具有柔性的聚合物分散液晶PDLC;测试了不同膜厚和混合比下的PDLC的电光特性和其光谱响应;从而得出了关于柔性聚合物分散液晶PDLC的一些实验规律和结论     

TiO2纳米颗粒对染料掺杂聚合物分散液晶的随机激光辐射特性的影响

随机激光的阈值与体系内的散射强度存在密切关系。高折射率二氧化钛(TiO_2)纳米颗粒与染料掺杂聚合物分散液晶(DDPDLC)均匀混合后,由于液晶微滴与TiO_2纳米颗粒之间的强散射作用,DDPPLC的随机激光具有更低的激光发射阈值,并且随TiO_2纳米颗粒的掺杂浓度而变化;在优化TiO_2纳米颗粒掺杂浓度的基础上,DDPDLC的发射阈值为270μJ/cm~2,线宽下降至0.08nm;温度实验证明了PDLC结构的散射是产生随机激光的主要工作机制,在TiO_2纳米颗粒掺杂后,DDPDLC样品依然保证了良好的可调性。     

聚合物分散液晶的制备及拉曼光谱分析

用溶致相分离的方法制备了以PMMA为基体的四种不同配比的聚合物分散液晶(PDLC),四氢呋喃为引发剂,并且通过傅立叶拉曼光谱仪对其进行检测,分析其光谱,观察各单体混合前后性质的变化,鉴别聚合物分散液晶的物质构成。此外,在指定的组分前提下,根据液晶最强峰与PMMA特征峰的相对强度拟合曲线得出PDLC中液晶与PMMA的质量百分比,为下一步研究聚合物分散液晶系统的光折变特性提供指导。     

便携式电控聚合物分散液晶全息透镜的电源及结构设计

根据聚合物分散液晶材料的光电特性及需要,在研究基于聚合物分散液晶光电器件时必须设计合适的电源驱动系统。介绍了在电控聚合物分散液晶全息透镜器件研制中,将电池输出的直流低压升高变频到70～100V、1000Hz频率交流高电压的电路系统设计。并介绍了变焦透镜装置总体结构的机械设计。实验结果表明,该电源设计能够满足聚合物分散液晶全息透镜器件中的液晶分子光轴驱动的需要,并能实现器件的小型化和便捷式。     

聚合物分散液晶膜的压光效应

报道了一种聚合物分散液晶(PDLC)膜在压力作用下从散射膜变为透明膜的实验现象,建议称之为PDLC膜的压光效应.介绍了与压光效应相关的PDLC的应变液晶、剪切液晶和拉伸液晶等概念;给出PDLC压光效应膜样品照片,偏光显微镜照片,电光特性光谱分析和压光效应光谱分析.提出PDLC膜压光效应的原理猜想,给出对PDLC膜光学性...     

光诱导液晶中偶氮聚合物形成相光栅的研究

报道了一种新型偶氮聚合物掺杂液晶的复合体系.该体系中的偶氮聚合物在光诱导下发生顺反式异构形成与液晶分离的相光栅.通过建立多指数模型研究该相光栅在He-Ne光的辐照下折射率的变化情况,并且通过对聚合物掺杂液晶的样品加上连续变化的电压来研究其对电场的响应过程.同时研究了聚合物的单体掺杂液晶后随光场和电场的变化情况.结果表明,光诱导下聚合物掺杂液晶的样品折射率改变值经45s达到饱和,弛豫时间为10min;单体掺杂时,饱和时间与弛豫时间分别为0.17s和0.9s.外加电场在1.0V、1.4V、2.6V和4.0V时光栅的衍射效率会突然下降,而单体在变化的外电场下衍射无明显变化.     

基于透射式液晶/聚合物光栅的分布反馈式激光器的研究

本文研究了染料掺杂透射式液晶/聚合物光栅的制备以及基于透射式液晶/聚合物光栅的分布反馈式激光器的激光特性.实验选取DCM作为激光染料,制备了周期为586 nm的掺杂DCM的透射式液晶/聚合物光栅;使用532 nm输出的Nd ∶YAG倍频脉冲激光器作为抽运光源对染料掺杂液晶/聚合物光栅进行侧面抽运,得到了中心波长为603 nm的窄线宽、低阈值激光输出.激光线宽为1.4 nm、阈值能量约为17.3 μJ,与之前国外的报道相比,阈值能量有了很大幅度的降低. 关键词： 液晶/聚合物光栅 分布反馈式激光器 阈值 线宽     

Optical spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12 doped with Pr

The silicates Ca₃Sc₂Si₃O₁₂, Ca₃Y₂Si₃O₁₂ and Ca₃Lu₂Si₃O₁₂, both undoped and doped with Pr³⁺ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca₃Sc₂Si₃O₁₂:Pr³⁺ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca₃Y₂Si₃O₁₂:Pr³⁺ and Ca₃Lu₂Si₃O₁₂:Pr³⁺ show features attributed to emission from two distinct sites accommodating the Pr³⁺ dopant. The decay kinetics of the Pr³⁺ 5d-4f emission in Ca₃Sc₂Si₃O₁₂:Pr³⁺ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.     

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi_1.5Zn_1.0Nb_1.5O₇/Ba_0.6Sr_0.4TiO₃/Bi_1.5Zn_1.0Nb_1.5O₇ tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2 nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO₂/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 °C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications.     

La0.67Ca0.33MnO3薄膜皮秒光电效应

在1064 nm波长脉冲激光（脉宽25 ps）的照射下，钙钛矿氧化物薄膜La0.67Ca0.33MnO3/SrTiO3具有超快光电效应，对激光脉冲显示ps量级的响应时间，上升沿响应时间300 ps，半高宽700 ps，同时，对激光能量的响应灵敏度为500 mV/mJ。     

Structure and magnetic order in La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 perovskites

In this paper we report the study of the perovskites La_0.7Ca_0.3Mn_0.5Co_0.5O₃ and La_0.8Sr_0.2Mn_0.5Co_0.5O₃ by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La_0.7Ca_0.3MnO₃ and La_0.8Sr_0.2MnO₃ destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites.     

合成反铁磁Ni81Fe19/Co90Fe10/Ru/Co90Fe10/Ni81Fe19的研究

采用直流磁控溅射方法制备了一系列的合成反铁磁及以其为自由层的自旋阀.研究发现,在Ni₈₁Fe₁₉与Ru层之间插入适当厚度的Co₉₀Fe₁₀层后,可有效地提高合成反铁磁两磁性层间的反铁磁耦合强度,得到具有饱和场H_s更高、饱和磁化强度M_s更低、热稳定性更好的合成反铁磁.另外,以这种合成反铁磁作自旋阀的自由层时,可有效提高自旋阀的稳定性. 关键词： 合成反铁磁 退火 自旋阀     

Depolarization currents in the Na0.5Bi8.5Ti2Nb4O27 and Na0.5Bi8.5Ti2Ta4O27 layered ferroelectrics

The influence of the prehistory on the electrical properties of layered ferroelectrics is investigated. It is established that the heating of short-circuited samples of the nonpolarized ceramic material Na_0.5Bi_8.5Ti₂Nb₄O₂₇ leads to the appearance of maxima of the current at temperatures below the Curie point only in the case of preliminary ageing of the samples. Original Russian Text ? A.I. Burkhanov, Yu.V. Kochergin, K. Bormanis, A. Kalvane, M. Dambekalne, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 7, pp. 1393–1394.     

Appearance of an inhomogeneous superconducting state in La0.67Sr0.33MnO3-YBa2Cu3O7-La0.67Sr0.33MnO3 trilayers

An experimental study of proximity effect in La_0.67Sr_0.33MnO₃-YBa₂CU₃O₇-La_0.67Sr_0.33MnO₃ trilayers is reported. Transport measurements on these samples show clear oscillations in critical current (I _c) as the thickness of La_0.67Sr_0.33MnO₃ layers (d _F) is scanned from ∼50 ? to ∼ 1100 ?. In the light of existing theories of ferromagnet-superconductor (FM-SC) heterostructures, this observation suggests a long range proximity effect in the manganite, modulated by its weak exchange energy (∼2 meV). The observed modulation of the magnetic coupling between the ferromagnetic LSMO layers as a function of d _F, also suggests an oscillatory behavior of the SC order parameter near the FM-SC interface.      

X-ray study of phase transitions in the system of solid solutions K2Pb4Nb10O30-Na2Pb4Nb10O30-K6W4Nb6O30

Boundaries of morphotropic phase transitions region in the system of solid solutions K₂Pb₄Nb₁₀O₃₀-Na₂Pb₄Nb₁₀O₃₀-K₆W₄Nb₆O₃₀ with the structure of the tetragonal tungsten bronze have been specified. Presence of the second morphotropic phase transition, perpendicular to the first one has been revealed. The temperature dependences of the structural parameters of some compounds have been investigated. The compounds with high values of Curie temperatures and working temperatures have been obtained.     

Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8

Incommensurate modulations in Ba₂TiSi₂O₈, Sr₂TiSi₂O₈, and Ba₂TiGe₂O₈ are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures.     

Phase formation and characterization of Sr3Y2Ge3O12, Sr3In2Ge3O12, and Ca3Ga2Ge3O12 doped by trivalent europium

This work reports on the phase formation during a solid-state reaction of Eu³⁺-doped garnets with the general formula A₃B₂Ge₃O₁₂ (A=Ca, Sr and B=Ga, In, Y) and their luminescent properties. It is shown by XRD and DTA/TG experiments that the garnet-phase formation is completed at 1100-1200 °C. Moreover, it turned out that the position of the oxygen to europium charge-transfer band and the intensity of the forbidden 4f-4f transitions of Eu³⁺ is dependent on the covalent interaction between the Eu³⁺ activator and the surrounding oxygen anions. The investigated red-emitting luminescent materials show high lumen equivalents and deep red emission at the same time, which makes them attractive for the application in LEDs (light emitting diodes), in particular for near UV-emitting LEDs.