Optical intensity gradient by colloidal photonic crystals with a graded thickness distribution

Gradient colloidal crystals with a thickness gradient were prepared by the vertical deposition technique with vertically graded concentration suspensions. The thickness of the gradient colloidal crystal gradually changes at different positions along the specific gradient direction of the crystal. The thickness gradient was determined by the concentration gradient, depending on the initial colloidal concentration and the settling time. The optical transmission intensity at the dip wavelength can be tuned by changing the thickness of the colloidal crystals. The gradient colloidal crystals lead to a gradient of optical intensity at the dip in transmission light. The gradient of optical intensity at the dip increases as the thickness gradient of the colloidal crystal increases.     

梯度结构胶体光子晶体的制备及光子禁带调节

以改进的对流自组装方法制备层数可控的胶体光子晶体, 并通过各向同性氧等离子体(O₂ Plasma)刻蚀构造出梯度结构, 进一步通过金(Au)及无定形硅(Si)的可控沉积调节梯度结构胶体光子晶体的光子禁带, 并将该梯度结构用于罗丹明B的荧光发射增强.     

基于胆甾相液晶的可调制光子晶体

将胆甾相液晶填充进胶体晶体内部空隙, 通过胆甾相液晶与胶体晶体的耦合, 构建了一种新型可调制液晶光子晶体. 填充于胶体晶体内部的胆甾相液晶织构呈现典型的手性近晶相(S)特征. 由于胆甾相液晶具有特定的选择性反射, 当胶体晶体的带隙处于胆甾相液晶的反射波长范围之内, 则随着温度的改变, 胶体晶体的带隙与胆甾相液晶的带隙同时发生蓝移. 在一定温度条件下, 胆甾相液晶的带隙将与胶体晶体的带隙发生耦合, 实现了光子晶体带隙在单峰与双峰之间的可逆切换.     

P(HEMA-co-AM)胶体晶体膜的制备及其性能

将聚苯乙烯胶体晶体嵌入丙烯酰胺(AM)与甲基丙烯酸羟乙酯(HEMA)的交联共聚膜中,制备了共聚物P(AM-co-HEMA)胶体晶体膜.研究了单体配比及交联剂N,N'-亚甲基双(丙烯酰胺)(MBA)对胶体晶体膜的光子带隙峰位置、拉伸强度和断裂伸长率的影响.结果表明:当n(HEMA)/n(AM)≤2.33时,光子带隙峰较明...     

上转换激光基质晶体BaY2F8的结晶习性

由BaY2F8晶体的结构特点和粉晶X射线衍射（XRD）数据,分析了该晶体的结晶习性。晶体结构中的强键为Y-F2-Y键,该键沿[001]方向伸展成链状,是晶体的优势生长方向。晶体的平衡稳定形态由斜方柱{130},{021}组成,晶体呈沿[001]方向发育的轴状习性。温度梯度法生长所得晶体的切片分析,证实了以上结论。BaY2F8晶体系采用提拉法等强制方法获得。     

聚合结晶化胶体阵列结构的压敏光响应性质

制备了由单分散聚苯乙烯微球构成的结晶化胶体阵列结构, 并制备了结晶化胶体阵列聚丙烯酰胺水凝胶薄膜. 通过微区反射光谱研究了其光子带隙位置随外加压力的变化规律. 实验结果表明, 该薄膜在垂直表面方向存在光子带隙, 并在一定载荷范围内带隙波长随外加压力呈可逆线性变化.     

Double telecom band thermo-optic switch based on dual-line filled photonic liquid crystal fibres

We demonstrate a thermo-optic switch based on photonic liquid crystal fibres (PLCFs) in which two lines of air hole are selective filled with liquid crystal (LC), with a high extinction ratio of more than 20 dB around 1310 nm and 1550 nm. Only in the range of 2.0°C it can perform a turn off and on operation of transmitted light in the second telecom band around 1550 nm while the first telecom bands around 1310 nm is still on. Due to the splitting of the bandgap, the switching function is achieved in this kind of PLCFs. Before the cleaning point (CP) of LC, a broad bandgap from about 1120 nm to 1320 nm splits into two ones, which are continuing inducing huge bandgap extension to shorter wavelength and longer wavelength after the CP of LC, respectively. Moreover, the temperature responses around the CP of LC is also investigated. Its sensitivity is about ?92.32 nm/°C around the CP of LC. Therefore, such kind of selective-filled PLCFs could find potential applications as thermo-optic switch and temperature sensor in the telecom band.     

基于温敏水凝胶的可调胶体晶体制备

基于单分散胶体粒子悬浊液在温敏水凝胶表面可以形成湿润型胶体晶体的现象, 利用温敏水凝胶对水的控释作用制备了温度敏感的可调制胶体晶体. 在室温下利用提拉法在温敏水凝胶聚N-异丙基丙烯酰胺(PNIPAAm)表面制备湿润型胶体晶体膜. 由于胶体粒子的有序排列, 胶体晶体显示出一个尖锐的反射峰. 当温度上升到34 ℃以上时, 由于PNIPAAm水凝胶中的水被释放, 导致胶体晶体中粒子浓度降低, 粒子间距增加; 反射峰发生红移. 这些特性可以通过温度变化进行调制.     

Control over the Wettability of Colloidal Crystal Films by Assembly Temperature

Summary: A facile method to fabricate colloidal crystal films with tunable wettability from an amphiphilic material polystyrene‐block‐poly(methyl methacrylate)‐block‐poly(acrylic acid) is presented. The wettability of the film can be tuned from superhydrophilic (CA, 0°) to superhydrophobic (CA, 150.2°) by varying the assembly temperature, while the position of the photonic bandgap of the colloidal crystal films remains virtually unchanged. The method could open new application fields of colloidal crystals in diverse environments.

The relationship of assembly temperature with water CA (inset is the water droplet profile of the relative water CA).     

Broadband reflection characteristic of polymer-stabilised cholesteric liquid crystal with pitch gradient induced by a hydrogen bond

A polymer-stabilised cholesteric liquid crystal (PSChLC) was fabricated by ultraviolet (UV) induced polymerisation of photopolymerisable acrylate monomers mixed in a cholesteric liquid crystal (ChLC). A polymer network with a concentration gradient, which was induced by UV light absorption of dye along the propagation direction, was formed. A hydrogen bond, arising between the polymer network with a concentration gradient containing carboxyl as proton donors and chiral dopant (CD) as proton acceptors, induced a pitch gradient in PSChLC and then, as a consequence, broadband reflection. The broadband reflection is associated with the concentration and the composition of photopolymerisable acrylate monomers, the concentration of CD and the polymerisation temperature. Examining the morphologies of the polymer network by scanning electron microscopy, the helix structure and pitch gradient were verified, confirming the pitch gradient of the PSChLC and revealing the essence of the formation of broadband reflection.     

Inward-growing self-assembly of colloidal crystal films on horizontal substrates

Colloidal crystal films have been fabricated on solid substrates with a horizontal deposition method. Scanning electron microscope images showed that the colloidal crystal films exhibit ordered face-centered cubic structures in large domains. Optical measurements demonstrated the presence of photonic band gap along the crystallographic [111] direction. The fabrication method described in this paper allows one to rapidly fabricate colloidal crystal films of different thicknesses, which can be controlled by varying colloidal suspension concentration or volume. In addition, the method also works well for growing colloidal crystal films on a hydrophilic solid substrate with a rough surface. Furthermore, the fabrication of colloidal crystal heterostructures has been demonstrated. An inward-growing mechanism responsible for self-assembly of colloidal spheres on horizontal substrates has been proposed to interpret the observed experimental results.     

Modulating Bandgap and HOCO/LUCO Energy of Semiconducting Polymer by Copolymerization or Incorporation of Electron Withdrawing/Releasing Groups

The modulation of bandgap and HOCO/LUCO energies of conjugated polymers by copolymerization or by incorporation of electron withdrawing/releasing groups is studied.The study was conducted by band structure calculation applying density functional theory with generalized gradient approximation.The polymers and copolymers were modeled as 1D infinite system with periodical boundary condition along the molecular direction.It is concluded that the bandgap and HOCO/LUCO energies of conjugated polymers depend on both electron withdrawing/releasing effects and non-bonding interaction between a side group and the conjugated systems.     

分子印迹胶体阵列检测对硝基苯酚

以对硝基苯酚(p-NP)为印迹模板,丙烯酰胺为功能单体,制备单分散的对硝基苯酚分子印迹胶体微球。通过垂直沉降法将分子印迹胶体微球自组装为分子印迹胶体阵列,采用胶带将分子印迹胶体阵列粘贴固定。固定于胶带上的分子印迹胶体阵列膜显示出良好的稳定性,而且对目标分子p-NP具有明显的光学响应。分子印迹微球吸附目标分子发生溶胀,引起胶体阵列溶涨,分子印迹胶体阵列(MICA)反射峰位置发生移动。实验结果显示,MICA随着p-NP浓度增加,反射峰红移近60 nm,MICA表面颜色由红色逐渐变为蓝紫色;而非印迹胶体阵列红移量只约40 nm。MICA简化了光子晶体凝胶传感材料的制备步骤,为开发新型高性能生化传感器材料提供了新思路。     

Spatial bandgap engineering along single alloy nanowires

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.     

Photon trapping by the internal Bragg reflection of colloidal crystals

Fluorescence light emitted from photoexcited rhodamine 6G (R6G) doped in colloidal crystals of exhaustively deionized colloidal silica suspension is partially trapped within a crystal cage. This photon trapping is caused by Bragg reflection in crystal lattices. The photon trapping efficiencies were quantitatively examined as a function of the thickness of measurement cell. The efficiency increased from about 40 to 60% as the cell thickness increased from 1 to 10 mm for an R6G concentration of 5×10⁻⁶ mol/L. This result is attributed to an increase in the number of crystal layers perpendicular to the observation direction; these are formed in the cell with a large optical path length. On the other hand, the trapping efficiencies were constant irrespective of the angle between the incident and observed light of the cylindrical cells. The constant efficiencies are attributed to the fact that the heterogeneous crystal layers around the inner cell wall have the same thickness.     

Dry etching of colloidal crystal films

Two types of non-close-packed colloidal crystal films were prepared by etching the films made of polystyrene nanospheres using a hyperthermal neutral beam of oxygen gas. Etching without sintering above glass transition temperature of the polymer particles resulted in the non-close-packed structure of the nanospheres, in which polystyrene nanospheres in different lattice planes touched each other due to the reduction in the size of the nanospheres that occurred during the etching process. In contrast, a different non-close-packed structure with inter-connecting networks between etched nanospheres was generated by annealing of the colloidal crystal and a subsequent etching process. The photonic bandgap could be tuned during this dry etching of colloidal photonic crystals. This connected open structure could be used as a template for a silica inverse opal by chemical vapor deposition. An alternative dry etching process, reactive ion etching, mainly affected the morphology of particles near the top surface, and only a slight change in the stop band position of the colloidal crystal film was observed.     

胶粒晶体模板法制备三维有序大孔材料

使用胶粒模板法制备三维有序大孔材料（three-dimensional ordered macroporous material,3DOM）是一个快速发展的领域。本文综述了3DOM的合成技术,包括各种填充模板的方法、模板的去除方法以及它们在光子晶体、催化材料、生物传感器以及医学等方面的应用前景。     

Photonic band structures of colloidal crystals measured with angle-resolved reflection spectroscopy

We acquired angle- and polarization-resolved reflection spectra from a colloidal crystal made of polystyrene spheres along the two perpendicular directions corresponding to the LU and LW directions in the first Brillouin zone of an fcc lattice. Dispersion relations between the reflection peak positions and the wave vectors of the incident light were obtained from the measured spectra and compared with calculated photonic band structures. For the first stop band region in the spectra, the behavior of the reflection peak due to Bragg diffraction agreed with the calculated band structure and revealed some differences induced by the polarization and crystalline orientations. The spectral features observed in the higher energy regions also revealed these differences. In addition, dispersion relationships between the peak positions and the wave vectors were obtained from the results of fitting each spectrum with several Gaussian curves, compared with the calculated photonic band structures. The relationships obtained for the LU direction almost matched the calculated band structure, while the relationships obtained for the LW direction revealed the features of the mixed band structure calculated for the two perpendicular directions. These results indicate that angle- and polarization-resolved reflection spectroscopy has the potential to experimentally analyze the photonic band structures of actual photonic crystals.     

A Mesoporous Superlattice Consisting of Alternately Stacking Interstitial Nanospace within Binary Silica Colloidal Crystals

A novel class of nonclassical structures of mesoporous silica, namely a binary nanoparticle mesoporous superlattice (BNMS), is obtained by the assembly of silica nanospheres of different sizes into a binary colloidal crystal. The colloidal crystal has a CrB‐type structure and consists of alternate stacks of unary fcc and binary AlB₂‐type structures along the b axis and has four types of interstitial mesopores. The BNMS can be deposited on a substrate by dip coating to form an oriented thin film in which the direction of the superstructure (b axis) is perpendicular to the substrate.     

Voltage-induced pseudo-dielectric heating and its application for color tuning in a thermally sensitive cholesteric liquid crystal

ABSTRACT

We previously proposed an electrical approach enabling the tuning of the center wavelength λ_c of the cholesteric liquid crystal (CLC) bandgap in the full-color visible spectrum based on the electro-thermal effect. The idea involved the design of a negative CLC with a thermally sensitive bandgap feature and the use of a sandwich-type cell with finite electrode conductivity, allowing the control of cell temperature by applied voltage via pseudo-dielectric heating. It has been demonstrated experimentally that the induced pseudo-dielectric heating is predominated by the pseudo-dielectric relaxation originating from the designated cell geometry. On the basis of this technique, key factors determining the tuning efficacy of the temperature and thus λ_c are primarily investigated in this study. Our results suggest that lowering the electrode resistivity and the specific heat conductivity of the cell can promote the maximum tunable temperature range. Expectedly, optimizing the electrode area, cell gap and dielectric permittivity of the CLC favors a decreased relaxation frequency and, in turn, reducing the voltage as well as the frequency required for λ_c tuning.