Pb0.56Sr0.44Zr0.52Ti0.48O3 (PSZT) inverse opal photonic crystals (PCs) have been synthesized by a process of self-assembly in combination with a sol–gel
procedure. PSZT inverse opals show pure perovskite structure with good orders in three dimensions. The evident photonic band
gaps have been observed in the transmittance spectra with a blue-shift phenomenon due to the decrease of opal template periods.
PSZT inverse opals also exhibit the reflection peaks in basic agreement with the calculated results. This three-dimensional
(3D) ordered PSZT inverse opals have shown interesting optical characteristics and potential applications in optoelectronic
and photonic devices. 相似文献
Opals are self‐assembled fcc‐packed colloidal crystals with sphere diameters in the nanometer and submicrometer region. The periodic dielectric structure leads to the opening of photonic band gaps that suppress the propagation of light with wavelengths at the lattice constant scale. This explains e.g. the opals' brilliant color impression. Synthetic opals can be prepared from polymer or metaloxide spheres in a bottom‐up approach that allows for chemical functionalization and processing. Also, they can be used as templates to fabricate inverted structures. Fields of application reach from optical chips, color displays and effect pigments to biosensors. 相似文献
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. 相似文献
The beauty of opals results from a densely packed, highly ordered arrangement of silica spheres with a diameter of several hundred nanometers. Such ordered nanostructures are typical examples of materials called photonic crystals, which can be formed by known microstructuring methods and by self‐assembly. Opals represent a self‐assembly approach to these structured media; such an approach can lead to novel materials for photonics, photocatalysis, and other areas. Although self‐assembly leads to many types of defects, resulting in the surprising and very individual appearance of natural opals, it causes also difficulties in technological applications of opal systems. 相似文献
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. 相似文献
Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion
luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant
effect on upconversion luminescence of Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap
overlapped with the emission band of Tb3+ ions. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
Optically amplified photochemistry with slow photons has been realized in our previous work when a photoactive material such as TiO(2) was molded into a photonic crystal and the corresponding energy of photonic bands overlapped with the electronic excitation. While numerous applications of photonic crystals have been proposed, the real practicality depends on the extent of structural imperfection that can be tolerated before significant deterioration in the optical response deems it unrealistic to use. As a result, it is important to evaluate the amount of structural disorder that can be tolerated in inverse TiO(2) opals if they are to be used as amplified photocatalysts for photolytic degradation of organics in environmental remediation and water purification. We present a systematic study on the effect of disorder with relation to the photocatalytic efficiency of oxidizing methylene blue dye adsorbed on inverse TiO(2) opals by introducing different fractions and sizes of guest spheres into the opal template. Our results show that half of the enhancement originally achieved by the inverse opal made from monodispersed 150-nm spheres is conserved when the domain size of the host spheres remains above a critical threshold. The substitution fraction can be as high as 0.4 when the guest spheres are 1.2 times larger than the host spheres. Such a high tolerance to structural disorder provides strong support for the potential use of inverse TiO(2) opals in environmental cleanup and water treatment applications. 相似文献
Artificial opals are self‐assembled colloidal crystals, which consist of a cubic dense packing (fcc) of hard (not film‐forming) colloids with diameters ranging from 200 to 900 nm. Because of their periodic nanostructure the assemblies are able to reflect light that matches their periodicity, i.e., UV‐ to IR‐radiation depending on the size of the colloids. Thus, they present a subgroup of ‘photonic crystals’. While, originally, the chemistry inside the colloids and the resulting opals was of minor significance, nowadays the chemical variation of opals is becoming more and more important for the preparation of functional and patterned opals. The search for functional opals is, therefore, especially focused on four topics: I) coloring agents, II) incorporation of fluorescent materials, III) replication, and IV) the controlled incorporation of defects.
The kinetics of nickel electrodeposition through a template of ordered polystyrene spheres is addressed experimentally and applied to prepare a series of metallic inverse opals with a non-integer number of layers. The observed layer-by-layer growth is discussed in terms of subsequently increasing disorder of the growth front. Reflection and transmission spectra of the samples demonstrate that the key optical features of these photonic crystals are most pronounced when the thickness does not essentially exceed two layers. The intensities and band positions can be additionally tuned by varying the height of the metal coating continuously, not discretely. These findings are confirmed semi-quantitatively by means of computational modeling of the spectra. Specific deposition current transients for in situ control of geometric parameters are discussed. 相似文献
The mechanism of enhancing the light harvesting efficiency of dye-sensitized TiO(2) solar cells by coupling TiO(2) inverse opals or disordered scattering layers to conventional nanocrystalline TiO(2) films has been investigated. Monochromatic incident photon-to-current conversion efficiency (IPCE) at dye-sensitized TiO(2) inverse opals of varying stop band wavelengths and at disordered titania films was compared to the IPCE at bilayers of these structures coupled to nanocrystalline TiO(2) films and to the IPCE at nanocrystalline TiO(2) electrodes. The results showed that the bilayer architecture, rather than enhanced light harvesting within the inverse opal structures, is responsible for the bulk of the gain in IPCE. Several mechanisms of light interaction in these structures, including localization of heavy photons near the edges of a photonic gap, Bragg diffraction in the periodic lattice, and multiple scattering events at disordered regions in the photonic crystal or at disordered films, lead ultimately to enhanced backscattering. This largely accounts for the enhanced light conversion efficiency in the red spectral range (600-750 nm), where the sensitizer is a poor absorber. 相似文献
Summary: This paper describes the synthesis and properties of functional opal structures, so-called colloidal photonic crystals (CPCs), from a variety of reactive polymers. Photoprocessable opals are presented as well as opals with incorporated “smart” defect layers that can be actively addressed by external stimuli. In addition, opals with functional bio-macromolecular defects have been developed. They present a new class of materials for optical biomonitoring through shifts of the induced photonic defect mode. Strong modification of photoluminescence according to the photonic bandstructure is observed from opals with embedded exclusively luminescent defect layer. 相似文献
In this study, inverse opal TiO2‐x photonic crystals (IO‐TiO2‐x) have been successfully synthesized by a two‐step calcination. The whole synthesis is safe and feasible. Additionly, the reduction degree and the structure of IO‐TiO2‐x can be precisely controlled. A series of IO‐TiO2‐x samples with different reduction degree were prepared and characterized. The TEM images show that the obtained samples possess a 3D‐ordered macroporous inverse opal structure. The reduced Ti atoms/oxygen vacancies were confirmed by Raman and XPS spectroscopy. All IO‐TiO2‐x samples showed better photoelectric properties than those of common TiO2 which indicates their great potential to be applied to photoelectric fields. The improvement of photoelectric properties is attributed to the efficient electron‐hole separation efficiency induced by moderately reduced Ti atoms/oxygen vacancies. Meanwhile, the 3D‐ordered macroporous inverse opal structure and the band gap are regulated to “capture” more solar energy. This new approach is proven to be a meaningful method to synthesize high‐performance TiO2 materials. 相似文献
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. 相似文献
The concept and analysis method of photonic crystals and band gaps are introduced into one-dimenslonal (1D) ordered mesoporous materials. MCM-41 type of materials are treated theoretically as photonie crystals. The formation of band gaps is exhibited and confirmed by a calculation of transfer matrix technique. PBG was found around 9-42 nm in soft X-ray region. The photonie band-gap was predicted to be dependent on incident direction, pore size and lattice constant. The mesoporous materials with different pore sizes and different lattice constants have different band-gap widths. 相似文献