Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 microm, produced by growing silicon inside the voids of an opal template of dose-packed silica spheres that are connected by small 'necks' formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to implement this technology self-assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self-assembly is also probably the approach entailing more materials aspects owing to the fact that they lend themselves to be fabricated by a great many, very different methods on a vast variety of materials and to multiple purposes. To these well-known material systems a new sibling has been born (photonic glass) expanding the paradigm of optical materials inspired by solid state physics crystal concept. It is expected that they may become an important player in the near future not only because they complement the properties of photonic crystals but because they entice the researchers' curiosity. In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.

In this work we propose and demonstrate a solution to the problems which arise when SiO2 monodisperse nanospheres of diameters under 300 nm or over 550 nm are used to obtain opal-based photonic crystals. If the nanospheres are too small, the sedimentation rate is very slow or even may not occur; if they are large enough, no significant order can be achieved because the velocity is too high. This method, based on the electrophoretic phenomenon, allows us to control the sedimentation velocity. Furthermore, other species of importance in this field, such as SiO2 spheres covered with a thick layer of TiO2, do profit from this method.

This article provides an overview of some recent developments related to the synthesis and functionalization of monodisperse colloidal spheres, a class of colloidal materials that has found widespread use in applications such as the fabrication of photonic crystals, optical sensing, and drug delivery. Traditionally, the choice of materials has been limited to polystyrene and silica. We and other groups have recently expanded the scope of materials by developing a number of methods for producing monodisperse colloidal spheres from various semiconductors and metals. This article is confined to our own work; it covers three different synthetic strategies: the bottom–up approach, the top–down approach, and template‐directed synthesis. The colloidal spheres may have a solid, hollow, or core–shell structure, and the chemical compositions can include Se, Bi, Pb, In, Sn, Cd, Pt, Ag2Se, CdSe, PbS, or TiO2. As an example to illustrate the attractive features of these colloidal spheres, we demonstrate the fabrication of Ag2Se‐based photonic crystals whose stop bands can be thermally switched between two spectral positions.

New ferrocenyl dendritic macromolecules based on flexible poly(propylenimine) dendrimer cores, built up to the fifth generation, containing 4, 8, 16, 32, and 64 peripheral ferrocenyl moieties, have been prepared and characterized. Solution electrochemical studies showed that all the ferrocenyl redox centers attached to the dendritic surface are electrochemically independent and that, in CH2Cl2 and THF as solvents, the neutral dendrimers undergo oxidative precipitation onto the electrode surfaces.

Germanium inverse opals with a full photonic bandgap in the NIR region are accessible by CVD. Deposition of digermane on sintered opals made of silica microspheres, followed by removal of the silica by etching, yields inverted Ge opals (see Figure for an SEM image of a cleaved edge, revealing the Ge layer) whose lattice parameters, network topology, and Ge coating thickness determine the optical properties of the inverse Ge opal.

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There is no doubt that silica study has had enormous interest for a long time since it is a material easy to obtain with a very inert chemical behavior. Among many relatively modern applications of silica such as optic fibers or its use as electrical isolator in microelectronics, we would like to emphasize its utilization to obtain artificial opals with very interesting optical properties. Submicron spheres of amorphous silica are fabricated by the Stöber-FinkBohn 1 (SFB) method; afterward these particles may be arranged by means of several techniques 2 which will produce a face centered cubic 3 (fcc) structure. A few years ago, it was proposed that periodical structures under special conditions could present photonic band gaps 4 (PBG), that is, energy ranges within which photons would not propagate regardless of the direction in which light is introduced. Unfortunately, artificial opals do not possess all the requirements to present a full PGB. Nevertheless, if opals are used as hosts where a high dielectric material is synthesized and the dielectric constant ( ) contrast between the guest material and spheres is high enough 5 (above 7.85), the conditions to obtain a full PBG are fulfilled, the refractive index of the medium being larger than that of the spheres. This means that the range of available materials is not very large as it must be taken into consideration that the high refractive index (n) material must be transparent in the frequencies where the photonic crystal works. The chances for a material to fulfill the conditions are increased if the opal is inverted 6 (removing silica spheres with a mild etching process once the opal has been loaded). In this way, the minimum value for the dielectric constant of the adequate guest material can be decreased. In this context, physical characterization of silica is fundamental to explain optical properties of bare opals and also important for optically monitoring the infiltration of opals with a dielectric. To date, silica refractive index 7 has been often assumed to be 1.45 for Stöber particles. Here it is proven this is the case only for very specific conditions of preparation.The refractive index of Stöber silica particles is studied, for the first time, to the best of our knowledge, as a function of calcination temperature. The motivation is that opals usually experience thermal treatments: sintering at 950°C to strengthen them or guest material synthesis, which often involves high temperatures.Five samples of spheres of different diameters (379, 575, 800, 870, and 1175 nm) were calcined at 11 temperatures in the following manner: each sample was divided in 11 parts of 100 mg of sample that were heated at 70°C for 3 h, then the temperature was increased (1°C /min) up to the desired point and maintained for 3 h, finally it was decreased down to room temperature (10°C /min). The refractive index of each sample was carefully measured with the Index Matching 8 (IM) method that consists of measuring the forward scattering intensity for 589 nm wavelength radia...