功能型聚合物光子晶体的制备及应用

光子晶体因其特殊的光调控性能,在各类高性能光学器件方面具有重要的应用前景.本文主要阐述了功能型聚合物光子晶体的制备方法及其在防护涂层、高效发光、高灵敏检测和高性能光信息存储等方面的应用.     

Fabrication of Inorganic Inverse Opals by Hetero-Colloidal Self-Assembly

We demonstrate the fabrication of inorganic inverse opals of silica and titania by a colloidal templating method. Hetero-colloids of polymeric particles and inorganic nanoparticles are formed and, on subsequent heat treatment, were found to yield inverse opals. The presence of nanoparticles does not interfere with the packing of the polymeric particles. The inverse opals exhibit photonic bandgaps in the wavelength of visible light that can be tuned by changing the size of the polymeric particles and the calcination temperatures.     

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.     

Hydrogel photonic sensor for the detection of 3-pyridinecarboxamide

Molecular imprinting is recognized as a powerful technique for preparing polymeric structures that contains tailor-made recognition sites for certain molecules. By combining a responsive hydrogel photonic crystal and molecular imprinting of 3-pyridinecarboxamide, polyacrylamide (PAM) imprinted photonic crystals (IPCs) with an inverse opal structure were prepared. They showed a rapid, recoverable, and selective response to 3-pyridinecarboxamide, which was detected by measuring the diffraction peak. The position of the diffraction peak could be tuned by copolymerizing acrylamide (AM) with acrylic acid (AA), by changing the ratio of AM to AA, by adding N,N'-methylene bisacrylamide to the monomers, or by imprinting molecules to monomers. More interestingly, the change in the Bragg diffraction of the IPCs can be directly converted into a readable optical signal that is visible to the naked eye without any labeling treatment.     

Process optimization of sol–gel derived colloidal photonic crystals

Three-dimensional photonic bandgap structures have been synthesized by a colloidal/sol–gel route, starting with the self-organization of polystyrene microspheres into opals by dip-coating, sedimentation or vertical convective self-assembly, followed by sol–gel infiltration of the interstices with silica, titania or a silica-titania mixture, by dip-coating and removal of the polymeric template. The structural and optical properties of the opals and inverse opals prepared by this method have been studied by scanning electron microscopy and visible infra-red spectroscopies to assess the relationship between their structure and the photonic properties obtained. The optical transmission and reflection spectra of the opal and inverse opal structures have also been simulated by the Translight Software code, using the Transfer Matrix method, for different numbers of stacked layers, showing reasonable agreement with the experimental results. By optimizing the fabrication parameters, colloidal photonic crystals of good quality have been obtained, with reduced defect concentrations and increased mechanical strength.     

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.     

均一取向等离子体二聚体的制备及光学机理

以单层SiO₂胶体微球为模板, 利用Au/SiO₂/Au交替沉积结合后退火处理的方法, 制备了一种垂直堆叠且均一取向的等离子体二聚体结构. 该方法具有很大的自由度, 可以通过调节实验流程来制备大面积取向相同的同质或异质纳米粒子二聚体. 所制备的纳米粒子的等离子体杂化效应明显, 在消光光谱中可以观察到成键及反键共振峰. 由于所得纳米粒子二聚体具有垂直堆叠的特殊规整取向, 还可以观察到所得样品等离子体吸收峰的角度依赖特性. 此外, 还探讨了Au/SiO₂/Au同质二聚体和Au/SiO₂/Ag异质二聚体的光学特性差异, 发现与Au/SiO₂/Au同质二聚体相比, Au/SiO₂/Ag异质二聚体由于Ag偶极等离子体模式与Au带间吸收的耦合而呈现Fano共振峰. 所得结果提供了一个调节贵金属等离子体光学共振峰位、 强度和波形的策略, 在纳米光子学领域有着广阔的应用前景, 对今后的实验和理论研究具有重要参考价值.     

三维光子晶体的制备

三维光子晶体作为一种光子带隙材料在光学器件、化学生物传感以及信息传输和存储等方面具有广泛的潜在应用价值。自1987年三维光子晶体的概念被提出以来,科学家们一直致力于在实验室用不同的手段合成不同材料和不同结构的光子晶体。本文综述了近年来出现的一些三维光子晶体制备方法,大致分为3类：“自上而下法”（top-down method）、“自下而上法”（bottom-up method）和模板辅助法（template-assisted method）,并详细阐述了每种方法的代表性工作、适用范围以及各自的优缺点。     

The Naked‐Eye Detection of NH3–HCl by Polyaniline‐Infiltrated TiO2 Inverse Opal Photonic Crystals

A reversible color change of a polyaniline‐infiltrated TiO₂ inverse opal photonic crystal (PC) film can be obtained when the PC is switched from an acidic to alkali vapor environment. In a saturated NH₃ environment, the stopband of the as‐prepared PCs changes from 556 to 688 nm; such large shift of 132 nm could be observed, corresponding to a clear color change from green to red. After placing in HCl vapor, the stopband undergoes a blue‐shift and the color turns back to green. The result is ascribed to PANI being doped or dedoped by acid or base and the effective refractive index of the PC film varying accordingly. The naked‐eye detection of NH₃ and HCl vapors can be realized by the reversible color change of the PC film, which is of importance for chemical and biological sensors.     

Directional Study of the Optical Properties of Tb3+‐ and Eu3+‐Doped Nanoparticles Embedded in Silica Photonic Crystals

The effects of the stop band (SB) in colloidal photonic crystals composed of silica spheres containing Eu³⁺‐ and Tb³⁺‐doped yttria nanoparticles are analysed. Reflection and transmission spectra indicate movement of the stop band, due to the 111 series of planes, towards shorter wavelengths with increasing angle of observation. The profile of the emission spectra is modified by the presence of the SB depending on the angle of measurement. Such a modification is more effective for a narrow emission band and it is thus more evident in the case of Tb³⁺ than Eu³⁺. An angular effect is also observed in the lifetime, which presents two maxima and one minimum. In the case of Tb³⁺ the maxima are at observation angles of 35 and 50°, and the minimum at 45°. We attribute this behaviour to penetration of the excitation beam at 475 nm modulated by the stop band. The ions excited in this way emit from different depths in the crystal, and therefore their lifetime will be affected differently by the same stop band, depending on the thickness of the crystal that must be crossed. Eu³⁺ shows a similar but less pronounced effect for two reasons: first, the main stop band (due to the 111 planes) is not effective at the excitation wavelength of 392 nm; second, the broadness of the Eu³⁺ emission is comparable to the width of the SB, and a decrease in the transition rate at the wavelength of the SB maximum is compensated by an increase at the sides of the SB.     

Modulation of spontaneous emission characteristics of Alq3 in three‐dimensional PMMA photonic crystals

The effect of the photonic stop bands (PSBs) on the spontaneous emission from tris(8‐hydroxyquinolinato)aluminum (Alq3) doped in the beads of polymethylmethacrylate opal photonic crystals (PCs) is investigated in detail. The structure of PSBs in PCs has been analyzed. The steady emission data exhibits that the first‐ and second‐order PSB could effectively influence the spectral characteristics of Alq3 through changing the incident angles. The emission dynamic data is also investigated by using the Kohlrausch strengthened exponential model, which shows that the emission decay rate of Alq3 can be decelerated as the PSB of PC approaches the emission peak of Alq3. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 842–847     

Focused ion beam micromachining and computation of polymeric photonic band gap

This article introduces a new approach to the achievement of low cost devices for optical telecommunications. For this purpose, the implementation of polymer components and of the WDM method show several advantages. A polymeric photonic band gap lattice can effectively assume demultiplexing at the wavelength of 1.55 μm without energy dissipation. First, the computation of the geometrical parameters designing a polymer photonic crystal by means of the finite‐difference‐time‐domain method, implemented with Bloch functions, is presented here. Second, the achievement of 2D polymer lattices by a dry process, the focused ion beam milling, is exposed. The experimental conditions for the achievement of a master are discussed on the basis of the milling performances and of the polymers physical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2993–3002, 2007     

自组装方法与三维光子晶体制作

光子晶体,特别是三维光子晶体,可能成为信息处理和通信等领域的新型功能材料.光子晶体的制作方法可分为"自上而下"的物理方法和"自下而上"的化学自组装方法.化学自组装方法是制作三维光子晶体最为经济有效的方法.本文在阐述自组装方法的种类、一般过程、优点和不足等内容的基础上,分别分析和总结了带有各种功能缺陷的三维光子晶体的制作,这些缺陷主要包括线缺陷、面缺陷和点缺陷.从研究中可以看出,化学自组装方法通常需要结合其他方法才能实现缺陷的嵌入.近些年,三维光子晶体制作在材料选取、结构设计和方法改进等方面都有一些最新进展,本文对此进行了较为详尽的评述,并对我们课题组的研究进行了总结.最后对光子晶体的研究和制作方向进行了展望.     

Templated‐Assembly of CsPbBr3 Perovskite Nanocrystals into 2D Photonic Supercrystals with Amplified Spontaneous Emission

Perovskite nanocrystals (NCs) have revolutionized optoelectronic devices because of their versatile optical properties. However, controlling and extending these functionalities often requires a light‐management strategy involving additional processing steps. Herein, we introduce a simple approach to shape perovskite nanocrystals (NC) into photonic architectures that provide light management by directly shaping the active material. Pre‐patterned polydimethylsiloxane (PDMS) templates are used for the template‐induced self‐assembly of 10 nm CsPbBr₃ perovskite NC colloids into large area (1 cm²) 2D photonic crystals with tunable lattice spacing, ranging from 400 nm up to several microns. The photonic crystal arrangement facilitates efficient light coupling to the nanocrystal layer, thereby increasing the electric field intensity within the perovskite film. As a result, CsPbBr₃ 2D photonic crystals show amplified spontaneous emission (ASE) under lower optical excitation fluences in the near‐IR, in contrast to equivalent flat NC films prepared using the same colloidal ink. This improvement is attributed to the enhanced multi‐photon absorption caused by light trapping in the photonic crystal.     

Fabrication and characterization of core-shell photonic crystals via a dipping process

High-quality polystyrene (PS) colloidal photonic crystals in large area were fabricated in 24 h via a capillary-enhanced process. Then, the photonic crystals with core-shell structure were obtained by incorporating silica nanoparticles into the interstitial space of opal template via a dipping process. The filling ratio (V_silica) of interstitial space could be manipulated by dipping colloidal crystals into suspensions with different concentrations of silica nanoparticles, which in turn renders the obtained core-shell photonic crystals. The absorptive peak of opal without dipping process is at 445 nm as measured by UV–vis spectrometry. The filling ratios of 0.130, 0.167 and 0.253 can be calculated according to the modified Bragg's Law, which corresponds to the absorptive peaks for core-shell opals at 453, 463 and 469 nm obtained from suspensions with silica nanoparticles of 0.017, 0.122, and 0.244 wt%, respectively. Therefore, by using this dipping process, the characteristic absorption wavelength for photonic crystal will be varied easily, efficiently and cost effectively than that by traditional methods for constructing opal from monodispersed colloids of different diameters.     

Optical and physical properties of iridescent photonic crystals obtained by self‐assembled polymethyl methacrylate nanospheres within graphene oxide nanoplatelets

Opal photonic crystals prepared by vertical templating of polymethyl methacrylate (PMMA) nanospheres in aqueous graphene oxide (GO) solutions were successfully obtained. The results show that increasing the PMMA nanospheres' size leads to the modification of the d‐spacing in GO nanoplatelets, inducing brilliant iridescence colors that span the entire visible electromagnetic spectrum. Scanning electron microscopy study shows a uniform distribution of GO nanoplatelets on the surface and the bulk of the opal photonic crystals. The reflectance spectra exhibit a significant red shift from 385 to 660 nm when the nanospheres' size increases from 160 to 306 nm, respctively. The Raman spectra show a systematic decrease in the intensity ratio of the D to G bands of GO (I_D/I_G), suggesting a partial reduction of graphene oxide with decrasing the extent of defects in the partially reduced GO nanoplatelets. This finding is confirmed by the significant decrease observed in the intensity of the hydroxyl band in the attenuated total reflectance mode‐Fourier transform infrared spectra of the photonic crystals. The results provide the first demonstrated example of intercalated assemblies of polymer nanospheres within GO nanosheets, leading to photonic crystals with brilliant iridescence colors that span the entire visible electromagnetic spectrum and can be tuned only by varying the size of the PMMA nanospheres.     

Amphibious sensor of temperature and refractive index based on D-shaped photonic crystal fibre filled with liquid crystal

ABSTRACT

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is ?88.2RIU^?1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of ?0.311°C^?1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments.     

Electrodeposition of 3D Ordered Macroporous Germanium from Ionic Liquids: A Feasible Method to Make Photonic Crystals with a High Dielectric Constant

A promising method for the production of germanium photonic crystals consists of electrodeposition of Ge from GeCl₄‐containing ionic liquids inside templates of polystyrene colloidal crystals and subsequent removal of the template. This room‐temperature method gives rise to the fabrication of a three‐dimensional highly ordered macroporous germanium nanostructure (see picture; scale: 2 μm) as a prototype of a photonic crystal.