We demonstrate a facile method for introducing planar defects into colloidal photonic crystals. Firstly, a 2D monolayer of SiO2 microspheres (guest spheres) was fabricated at the air/water interface by compressing the individual microspheres with a surfactant into long-range hexagonal arrays. The floating monolayer, which served as our defect layer, was then transferred onto a pre-deposited colloidal crystal slab consisting of PS@SiO2 microspheres (host spheres). Subsequently, a second colloidal crystal slab of host spheres was deposited on the surface of the defect layer. In comparison to previous methods to introduce planar defects into colloidal photonic crystals, this fabrication results in pronounced passbands in the band gaps of the colloidal photonic crystals. More importantly, the FWHM of the passband in our experiment is just 16 nm, which is narrower than the previously reported results to the best of our knowledge. Furthermore, the defect modes can be engineered by changing the diameter of the guest spheres and/or transforming the host spheres from PS@SiO2 spheres to hollow SiO2 spheres by calcination. The measured defect modes in the spectra match well with the simulated results.

Colloidal photonic crystals (CPCs) are a type of photonic crystals that are made of periodically arranged submicron spheres. Because of the unique advantages of cost-effectiveness, easiness and relatively large scalability for their fabrication, they have attracted a great deal of research interest for a wide range of applications. However, most of the CPCs are made of spherical building blocks with face-centred-cubic lattice, which bears only a pseudo photonic bandgap between the second and third bands. Theoretical simulation has suggested that lowering the symmetry of the building blocks or the dielectrics of the materials can potentially open a full bandgap, namely, the complete photonic bandgap. In this paper, recent efforts towards this end were thoroughly reviewed and summarised from three aspects: the symmetries of the building blocks, the crystalline lattices and the dielectrics of materials. In the end, a conclusion was given to the recent research in this field and related challenges were outlined. A promising outlook was proposed for the future direction along with its impact to the scientific community.

Centimetre-sized single crystalline calcite inverse opals (IOs) were fabricated by the combination of vapour diffusion and epitaxial growth methods in the template of colloidal crystals. The crystallinity of the IOs is closely related to the surface chemistry of the templates.

Hollow silica microspheres with holes of tunable numbers and sizes on the shell wall were prepared in this study. Clusters with positively charged polystyrene (PS) microspheres as the central spheres (CSs) and negatively charged PS spheres as the “halo” spheres (HSs) were formed via electrostatic interactions and utilized as a template. In the subsequent silica coating process, only CS was selectively coated; hence, after calcination, porous hollow silica microspheres were obtained.

We demonstrate photonic crystal lasing with a low threshold power of ∼10 μJ per pulse from a dye with a high luminescence quantum yield and weak self-quenching effect. The effects of the stop bands of photonic crystals and concentration of doped dye on the threshold of lasing were systematically investigated.

Patterning colloidal photonic crystals are a first step to the realization of integrated photonic circuits. In this paper, we introduce a new way to pattern colloidal photonic crystals by applying ultrasonication to selectively remove certain parts of the colloidal photonic crystal film from the substrate. These patterns with hydrophobicity can further function as templates to direct the growth of another layer of colloidal photonic crystal in order to reach dual-patterned photonic crystals with distinct hydrophilic and hydrophobic domains. The dual-patterns are responsive to water vapor, which can reversibly switch the reflection color of the hydrophilic regions on and off many times, while the hydrophobic parts are almost unaffected.

Oxygen plasma etching of electrospun polymer fibers containing spherical colloids is presented as a new approach towards anisotropic colloidal nanoparticles. The detailed morphology of the resulting nanoparticles can be precisely controlled in a continuous way. The same approach is also amenable to prepare inorganic nanoparticles with double-sided patches.

This communication describes the transformation of a colloidal crystalline lattice that was realized via oxygen plasma etching of colloidal crystals made of SiO2@PMMA core−shell microspheres. The plasma etching of the colloidal crystals proceeded nonuniformly from the top to the bottom of the colloidal crystals. The PMMA shell was etched away by the oxygen plasma in a layer-by-layer manner, and the silica core was drawn into the pit formed by the neighboring spheres in the layer below. Consequently, the crystalline lattice was transformed while the order was maintained. Scanning electron microscopy images and reflection spectra further confirmed the change in the crystalline structures. Colloidal crystals with sc and bcc lattices can be fabricated if the ratio of the polymer shell thickness to the silica core diameter is equal to certain values. More importantly, this approach may be applicable to the fabrication of various assembly structures with different inorganic particles.

We combine the most efficient (chemical) approach toward three-dimensional photonic crystals with the most convenient (physical) technique for creating non-close-packed crystalline structures. Self-assembly of colloidal particles in artificial opals is followed by a carefully tuned plasma etching treatment. By covering the resulting top layer of more open structure with original dense opal, embedded defect layers and heterostructures can be conveniently designed for advanced photonic band gap and band edge engineering.

We present a self-assembly approach for monolayer and multilayer deposition of ellipsoids with a controllable direction. The direction of the ellipsoids in the assembly can be conveniently tuned by external applied magnetic field. This level of control on positional and directional order suggests a way to build monolayer templates for lithography with two-dimensional patterns and three-dimensional anisotropic photonic crystals, which may open the way toward the complete photonic band gap in the visible.

Monodisperse ellipsoids were synthesized by continuous coating of silica on hematite spindle cores. Spindle cores with decreasing aspect ratio were obtained by decreasing the molar ratio of Fe3+ and H2PO4−. Using PVP molecules as the surface stabilizer for silica coating, the aspect ratio of the ellipsoids can also be tuned by altering the amount of added TEOS. These monodisperse ellipsoids with well controlled sizes and aspect ratios can be regarded as the potential building blocks for self-assembly.

Three-dimensional photonic crystals (or photonic band gap materials) have been fabricated with oblate spheroids as the photonic building block. The nonspherical shape was realized by the blown film extrusion process of a prefabricated colloidal photonic crystal of spherical polystyrene particles, with its voids infiltrated by polyvinyl alcohol. The extrusion was applied on the composite film at a temperature above the glass transition temperature of both polymers. The uniformly applied two-dimensional stretching retains the positional order in the prefabricated colloidal crystal; transforms the spheres into oblate spheroids; and results in orientational order between the spheroids. The morphology of the particles can be predictably changed from a sphere into an oblate spheroid with a specified aspect ratio by the extent of the blown film extrusion. Therefore, the concomitant photonic band gap properties can be tuned in a convenient way.

A ternary system, consisting of air, an air-core/dense-silica-shell core−shell particle, and liquids has been used to fabricate an inverse opal structure with low fill factor, high refractive index contrast, and reversible tuning capabilities of the bandgap spectral position. The original close-packed opal structure is a ternary self-assembled photonic crystal from monodisperse and spherical polystyrene-core/silica-shell colloidal particles with air as the void material. Calcination removed the polystyrene and converted the core−shell particles to hollow spheres with a dense shell. In a final step, liquid is infiltrated only in the voids between the hollow spheres, but does not penetrate in the shell. This allows facile and reversible tuning of the bandgap properties in an inverse opal structure.

We demonstrate a facile method for introducing planar defects into colloidal photonic crystals. Firstly, a 2D monolayer of SiO2 microspheres (guest spheres) was fabricated at the air/water interface by compressing the individual microspheres with a surfactant into long-range hexagonal arrays. The floating monolayer, which served as our defect layer, was then transferred onto a pre-deposited colloidal crystal slab consisting of PS@SiO2 microspheres (host spheres). Subsequently, a second colloidal crystal slab of host spheres was deposited on the surface of the defect layer. In comparison to previous methods to introduce planar defects into colloidal photonic crystals, this fabrication results in pronounced passbands in the band gaps of the colloidal photonic crystals. More importantly, the FWHM of the passband in our experiment is just 16 nm, which is narrower than the previously reported results to the best of our knowledge. Furthermore, the defect modes can be engineered by changing the diameter of the guest spheres and/or transforming the host spheres from PS@SiO2 spheres to hollow SiO2 spheres by calcination. The measured defect modes in the spectra match well with the simulated results.

Colloidal photonic crystals (CPCs) are a type of photonic crystals that are made of periodically arranged submicron spheres. Because of the unique advantages of cost-effectiveness, easiness and relatively large scalability for their fabrication, they have attracted a great deal of research interest for a wide range of applications. However, most of the CPCs are made of spherical building blocks with face-centred-cubic lattice, which bears only a pseudo photonic bandgap between the second and third bands. Theoretical simulation has suggested that lowering the symmetry of the building blocks or the dielectrics of the materials can potentially open a full bandgap, namely, the complete photonic bandgap. In this paper, recent efforts towards this end were thoroughly reviewed and summarised from three aspects: the symmetries of the building blocks, the crystalline lattices and the dielectrics of materials. In the end, a conclusion was given to the recent research in this field and related challenges were outlined. A promising outlook was proposed for the future direction along with its impact to the scientific community.

Oxygen plasma etching of electrospun polymer fibers containing spherical colloids is presented as a new approach towards anisotropic colloidal nanoparticles. The detailed morphology of the resulting nanoparticles can be precisely controlled in a continuous way. The same approach is also amenable to prepare inorganic nanoparticles with double-sided patches.

Patterning colloidal photonic crystals are a first step to the realization of integrated photonic circuits. In this paper, we introduce a new way to pattern colloidal photonic crystals by applying ultrasonication to selectively remove certain parts of the colloidal photonic crystal film from the substrate. These patterns with hydrophobicity can further function as templates to direct the growth of another layer of colloidal photonic crystal in order to reach dual-patterned photonic crystals with distinct hydrophilic and hydrophobic domains. The dual-patterns are responsive to water vapor, which can reversibly switch the reflection color of the hydrophilic regions on and off many times, while the hydrophobic parts are almost unaffected.

We demonstrate photonic crystal lasing with a low threshold power of ∼10 μJ per pulse from a dye with a high luminescence quantum yield and weak self-quenching effect. The effects of the stop bands of photonic crystals and concentration of doped dye on the threshold of lasing were systematically investigated.