光子晶体的制备与应用进展

光子晶体概念的提出到现在已有20多年,由于其特有的带隙和缺陷结构可实现对光子传播的控制,与传统的基于半导体晶体的电子技术相比更具优势,是未来光子计算机和光子通讯技术研发的核心。近年来,基于新材料、新方法制备的具有复杂结构的光子晶体不断涌现,其应用范围也从较早的波导、光开关、反射镜拓展到传感器、超棱镜、微透镜、太阳能电池、增强LED发光、光存储、生物芯片、仿生等新兴领域。本文结合了最新的研究状况,探讨了光子晶体的制备与应用进展。     

蛋白石及反蛋白石結構光子晶體

光子晶体是由不同介电常数的材料构成的一种空间周期性结构，它能够在特定方向上禁阻、控制和操纵光子的运动。目前，已制备的光子晶体具有几种不同的结构类型，本文主要综述了蛋白石、反蛋白石结构光子晶体的制备方法及其光子带隙的影响因素。     

Doped colloidal photonic crystal structure with refractive index chirping to the [111] crystallographic axis

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.     

化学响应性光子晶体

光子晶体是一种具有光子带隙结构的周期性电介质材料,如果将响应性材料组装到光子晶体结构中,所形成的光子晶体的带隙结构则对外界环境的变化具有响应性,而被称为响应性光子晶体。响应性光子晶体作为光子晶体的一个新领域,由于其在传感器,生物医学,临床检测等方面的潜在应用,近几年受到广泛关注。根据外界环境的不同,响应性光子晶体可简单分为化学响应性光子晶体、物理响应性光子晶体和生物响应性光子晶体等。本文将对化学响应性光子晶体的国内外研究动态做一简要介绍,重点介绍以下五种化学响应性光子晶体:金属离子响应光子晶体、pH响应光子晶体、氧化还原响应光子晶体、葡萄糖响应光子晶体和光化学响应光子晶体。     

光子晶体的制备及应用

光子晶体（PC）是具有光子带隙的周期性电介质结构，频率落在光子带隙中的光将被禁止传播。本文对光子晶体的能带结构、带隙的产生、制备方法及应用作了简要的介绍，重点介绍了光子晶体的制备技术及其在光电领域中的应用前景。     

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.     

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.     

具有然陷模的氧化铝光子晶体的光学传感性能

采用在周期性氧化电压信号中插入恒压波形的方法成功制备了具有缺陷模的一维氧化铝光子晶体. 这种晶体的透射光谱研究表明,缺陷的厚度对缺陷模的透过率具有显著影响,当缺陷厚度在180 nm时,光子禁带内部出现透过率为55%、半峰宽约为18 nm的缺陷模. 该缺陷模能够对进入到氧化铝孔道内部的液体物质做出响应,其位置与液体的折射率线性相关.     

Thermoresponsive inverse opal films fabricated with liquid-crystal elastomers and nematic liquid crystals

Liquid-crystal elastomers together with nematic liquid crystals have been used as inverse opal materials to fabricate thermoresponsive photonic crystal directly. In the vicinity of the phase-transition point of the mixture, the photonic band gaps of such inverse opal films exhibited a strong temperature dependence. As the molar ratio of liquid-crystal elastomers and nematic liquid crystals changed, the character of their PBGs also changed with increasing temperature. Such a temperature-tuning effect in the photonic band gap should be of great interest in thermal switches and thermal sensors.     

Polystyrene@TiO2 core-shell microsphere colloidal crystals and nonspherical macro-porous materials

High-quality and stable PS@TiO(2) core-shell microsphere colloidal crystals were prepared by electrostatic colloid stabilization combined with two-substrate vertical deposition method. The polyelectrolyte stabilized colloids self-assembled into face-centered cubic arrays with the (111) face perpendicular to the substrate. These colloidal crystals are gifted with high mechanical stability toward the flow of solution. Structure-property correlations were made using scanning electron microscopy and UV-vis-NIR spectroscopy. Optical spectra showed the presence of an L-stopband peak in the photonic band structure. Besides, these PS@TiO(2) colloidal crystals can be used as templates to fabricate the nonspherical macro-porous materials, and complete band gaps can be more easily obtained from such structure than from their spherical counterparts due to their lower symmetries. This work will hold the promise of enhanced photonic band gap materials.     

Opal and inverse opal photonic crystals: Fabrication and characterization

Three-dimensional photonic crystals made of close-packed polymethylmethacrylate (PMMA) spheres or air spheres in silica, titania and ceria matrices have been fabricated and characterized using SEM, XRD, Raman spectroscopy and UV–Vis transmittance measurements. The PMMA colloidal crystals (opals) were grown by self-assembly from aqueous suspensions of monodisperse PMMA spheres with diameters between 280 and 415 nm. SEM confirmed the PMMA spheres crystallized uniformly in a face-centred cubic (fcc) array, and UV–Vis measurements show that the colloidal crystals possess pseudo photonic band gaps in the visible and near-IR regions. Inverse opals were prepared by depositing silica (SiO₂), titania (TiO₂) or ceria (CeO₂) in the voids of the PMMA colloidal crystals using sol-gel procedures, then calcining the resulting structure at 550 °C to remove the polymer template. The resulting macroporous materials showed fcc ordering of air spheres separated by thin frameworks of amorphous silica, nanocrystalline titania or nanocrystalline ceria particles, respectively. Optical measurements confirmed the photonic nature of the inverse opal arrays. UV–Vis data collected for the opals and inverse opals obeyed a modified Bragg’s law expression that considers both diffraction and refraction of light by the photonic crystal architectures. The versatility of the colloidal crystal template approach for the fabrication of macroporous oxide structures is demonstrated.     

Recent advances in spherical photonic crystals: Generation and applications in optics

Spherical photonic crystals (PCs), generated by assembly of monodisperse colloidal nanospheres in a spherical confined geometry, attract great attention recently owing to their potential applications in the fields of displays, sensors, optoelectronic devices, and others. Compared to their conventional film or bulk counterparts, the optical stop band of the spherical PCs is independent of the rotation under illumination of the surface of a fixed incident angle of the light, broadening their applications. In this paper, we will review recent advances in the field of spherical PCs including design, preparation and potential applications. Various preparation strategies for spherical PCs, including solvent-evaporation induced crystallization method, microfluidic-assisted approach, and others are outlined. Their applications based on the unique optical properties (such as photonic band gaps and structural colors) for sensing and displaying are then presented, followed by the perspective of this emerging field.     

Directional fluorescence spectra of laser dye in opal and inverse opal photonic crystals

We have investigated the fluorescence from R6G dye molecules embedded in fcc photonic crystals with a large range of lattice parameters. Both polystyrene opals and alumina inverse opals are studied, allowing us to compare direct and inverted structures. We observe clear stop bands in the fluorescence spectra, whose center positions, widths, and depths are analyzed and compared to stop bands from reflectivity measurements. In the frequency range of first-order stop gaps, the measured stop band centers and widths agree well with theoretical predictions. The depths are interpreted in terms of the mean free path (disorder) and the Bragg attenuation length (order). We observe intriguing enhanced emission at the blue side of the stop bands, which is attributed to the escape of diffuse light from the photonic crystal (related to both order and disorder). We perform the first experiments in the range of second-order stop gaps, which is the regime where the photonic band gap is anticipated. We observe complex multiple-Bragg features that correlate favorably with reflectivity peaks.     

Photo-induced Birefringence of Azo-dye Based on Three-dimensional Opal Photonic Crystals

A series of three-dimensional opal photonic crystals based on the polymer was synthesized and applied in the field of photo-induced birefringence. The data show that the photo-induced birefringence(PIB) of pure Sudan III film could be enhanced by increasing the thickness of azo films. When Sudan III was distributed on the three-dimensional opal photonic crystals, the photo-induced birefringence process could be modulated. In addition, the data also exhibit that the PIB processes with different pumping polarization directions are sensitive to the role of photonic crystals. The results could be beneficial to further understanding the photo-induced birefringence and utilizing the photonic crystals.     

三维SiO2欧泊模板溶剂热法制备硫化锌光子晶体

以单分散二氧化硅微球在重力场下自组装得到的三维有序欧泊(opal)为模板，采用溶剂热法在模板空隙内生长ZnS晶体，从而制备高质量的硫化锌基光子晶体. 通过X射线衍射(XRD)和Raman光谱证明ZnS晶体为闪锌矿结构且晶体质量较好，并对其生长机理进行了讨论. 通过场发射扫描电子显微镜(FESEM)和紫外-可见分光光度计对所合成的ZnS/opal复合物与ZnS反欧泊结构进行了表征，结果表明两种结构都保持了欧泊三维有序性，并且在Г-L方向(垂直于(111)方向)上出现了布拉格衍射峰，说明其具有良好的光子晶体特性.     

Engineering Nanoarchitectures for Photonic Crystals

The detailed shape of the dense material network of inverse opals has a significant influence on the appearance of band gaps in these photonic crystals. One example of these topologically very similar networks is the skeleton structure, which can show two complete band gaps. Like all inverse opals, these structures are self‐standing and can be fabricated via self‐assembly strategies. The first step for obtaining these novel kind of photonic crystals has been achieved by synthesizing a titania skeleton structure.     

Photoswitching properties of photonic band gap material containing azo-polymer liquid crystal

A photochemically tunable photonic crystal was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO₂ inverse opal structure. The SiO₂ inverse opal film infiltrated with the polymer LC reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the reflection band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anisotropic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable not only for various optical materials, but also for introduction of defects in the photonic crystals.     

Responsive photonic crystal for the sensing of environmental pollutants

This review covers the concepts of photonic crystal (PhC) and its usage for the sensing of environmental pollutants. PhCs are composed of periodic and ordered nanostructures which can manipulate the diffraction or reflection of light propagation through the structures. If the light spectra locate in the visible range, the color of materials can be observed by naked eye. The optical properties of PhCs are determined by the lattice constant of the crystal or by the refractive index contrast between the colloids and the surrounding medium. Based on these features, responsive PhCs can be designed to detect the environmental pollutants. In this review, we primarily described the photonic crystals for the sensing of volatile organic compounds (VOCs), organophosphates (OPs), heavy metal ions and endocrine disrupting chemicals (EDCs), and these sensors exhibited excellent sensitivity and are promising for the on-site monitoring of pollutants.     

Electrochromic photonic crystal displays with versatile color tunability

An electrochromic photonic crystal (EPC) display device that combines chemical (electrochromic) and physical (photonic) coloring mechanisms is reported for the first time. This EPC exhibits superior and versatile color tunability. The TiO₂ inverse opals fabricated by atomic layer deposition are adopted as EPC material. Results show that the photonic band gaps selectively modified the optical properties of the EPC and enabled facile tuning of electrochromic colors. In addition, the reversible photonic and photonic modified electrochromic coloring states with insertion/extraction of lithium ions enable novel and promising approaches for future display applications.     

FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

A novel technique was used to fabricate three-dimensional photonic crystals with superlattices. The super structure was fabricated by assembling monodispersed microspheres in the grooves of the scales of morpho butterfly, which makes the photonic crystal being composed of two kinds of different photonic structures (natural groove structure of butterfly wing and artificial microspherical colloids arrangement). The superstructural photonic crystal exhibits some unique optical properties different from both the butterfly wing and the colloidal crystal. The approach exhibited here provides a new way for fabricate photonic crystals with superlattices.