Fluoride materials for optical applications: Single crystals, ceramics, glasses, and glass–ceramics

Fluoride compounds have compelling advantages for many optical applications due to their unique combination of low phonon energy, high UV absorption edge energy, and relatively weak crystal field. In this article, we offer a concise review of the current state of the art in fluoride single crystals, ceramics, glasses, and glass–ceramics for optical applications.     

Copper-based nanowire materials: templated syntheses, characterizations, and applications

Well-aligned Cu(OH)2 nanoribbon and CuO nanorod arrays have been prepared on copper substrates by liquid-solid reactions. The effects of temperature, reaction time, solvent, and pH value on the morphology and composition of the products are systematically studied. Using the Cu(OH)2 nanoribbons array as a reactive and sacrificial template, we have successfully synthesized Cu2O, Cu9S8, and Cu nanoribbon/ nanowire arrays, demonstrating the versatility of the template. The extensive series of copper-based one-dimensional nanomaterials have been fully characterized by various structural, microscopic, and spectroscopic techniques. Moreover, the Cu nanowires are demonstrated to be an excellent surface-enhanced Raman scattering substrate with a sensitivity over an order of magnitude higher than that of a common roughened copper electrode.     

Transparent perfluoropolyethers for vacuum ultraviolet applications

After a broad scouting based on quantum chemical calculations, optical absorption measurements in the vacuum ultraviolet (VUV) wavelength region between 140 and 190 nm were performed on a narrower series of commercial and experimental liquids. By elimination of sources of external contamination, mainly due to atmospheric gases, the analysis of the contributions to the absorption related to the backbone structure and to the chain end composition allowed the synthesis of a novel family of linear perfluoropolyethers (PFPEs) with optical absorbance at 157 nm between 0.3 and 0.6 cm(-1) in a broad range of compositions and molecular weights. The dependence of the optical threshold on the PFPE composition demonstrates that -OCF2- is the most transparent segmental unit in the VUV region.     

Biosensing with polydiacetylene materials: structures, optical properties and applications

Polydiacetylene (PDA) materials are used as a platform for detection of biological analytes such as microorganisms, viruses and proteins. The environmentally responsive chromic and emissive properties of the polymer, combined with self-assembled material formats, make these materials particularly attractive for biosensing applications. A variety of approaches have been used in developing these materials and demonstrating their potential for biological detection. In this feature article we describe different PDA material formats, discuss the optical properties that are the basis for signal generation, and review the use of PDA for biosensing.     

Aurivillius-type ceramics, a class of high temperature piezoelectric materials: Drawbacks, advantages and trends

The obtention of reliable and high performance piezoelectric ceramics for uses at high temperatures is still an open issue in the field of electroceramics. The materials used nowadays for such applications present limitations due to different causes: low piezoelectric coefficients, difficulties in processing that lead to the necessary use of single crystals, high cost of raw materials and more. In this sense, an increasing interest in materials with the so-called Aurivillius-type structure has occurred during recent years, due to their relatively high piezoelectric coefficients and high ferro–paraelectric phase transition temperature. However, some difficulties must be overcome, such as processing for obtaining highly dense ceramics and determining their real piezoelectric behaviour at high temperature. In this work, a review of the processing and properties of ceramics with this structure is shown. Effects of the use of precursors obtained by an alternative route mechanical activation on the microstructure are explained. A complete piezoelectric characterization at working temperatures (>300 °C), barely found in the literature, is also shown. The effects of trapped charges in the dielectric permittivity and in the piezoelectric radial resonance are also discussed.     

Revisiting ceramics for medical applications

The most significant demand for biomaterials has emerged as a consequence of the need to provide clinical treatment to a large number of patients. The search for potential solutions produces a large demand for materials suitable for bone repair or replacement. Calcium phosphates, bio-glasses, bio-glass ceramics and ordered silica mesoporous materials, among other types of materials, will be reviewed and studied from the point of view of their potential applications as replacement materials in bone repair and regeneration, as potential substrates in tissue engineering, and also as drug delivery systems. An overview on the present achievements, but also on the "missing links" will be presented.     

Preparation of Transparent, Partially-Crystallized BaTiO3 Monolithic Xerogels by Sol-Gel Processing

Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90°C) have been successfully synthesized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentration range of 1.0 mol/l with addition of water with a molar ratio of H2O/Ba 6.3. Transparent monolithic xerogels obtained from a precursor solution of 1.0 mol/l remained transparent even after firing at 500°C in oxygen, although the degree of their transparency was considerably decreased. Firing at temperatures above 500°C yielded translucent ceramics of BaTiO3, and ultimately, firing above 600°C resulted in normal opaque ceramic bodies. Those obtained from a more concentrated precursor solution of 1.2 mol/l were, on the other hand, still transparent after firing at 600°C in oxygen, and turned opaque at 700°C. The results demonstrate that the materials retained their transparency even after pyrolysis of organic compounds involving exothermic oxidation at temperatures in the range of 200 to 400°C. The densification behavior of transparent BaTiO3 monolithic xerogels obtained was found to be excellent; for example, those derived from a 1.0 mol/l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of 1 m by firing at 1100°C for 2 h in oxygen.     

Tin-based halide perovskite materials: properties and applications

Organic–inorganic hybrid halide perovskite materials have attracted considerable research interest, especially for photovoltaics. In addition, their scope has been extended towards light-emitting devices, photodetectors, or detectors. However, the toxicity of lead (Pb) element in perovskite compositions limits their applications. Therefore, a tremendous research effort on replacing is underway. More specifically, tin-based perovskites have shown the highest potential for this purpose. However, many challenges remain before these materials reach the goals of stability, safety, and eventually commercial application. This perspective considers many aspects and the critical development possibilities of tin-based perovskites, including drawbacks and challenges based on their physical properties. Additionally, it provides insights for future device applications that go beyond solar cells. Finally, the existing challenges and opportunities in tin-based perovskites are discussed.

This perspective presents the current status and prospects of tin-perovskites and the relevant optoelectronic device applications.     

New carbon materials: biological applications of functionalized nanodiamond materials

Nanoscale diamond particles have become an interesting material. Due to their inertness, small size and surface structure, they are well-suited for biological applications, such as labelling and drug delivery. Here we discuss the surface structure and functionalisation of diamond nanoparticles. Non-covalent as well as covalent grafting of bioactive moieties is possible, and first applications of fluorescent diamond nanoparticles are described.     

Smart polymeric materials: emerging biochemical applications

Smart polymeric materials respond with a considerable change in their properties to small changes in their environment. Environmental stimuli include temperature, pH, chemicals, and light. "Smart" stimuli-sensitive materials can be either synthetic or natural. This review discusses the application of smart materials as tools to solve biological problems such as bioseparation, drug delivery, biosensor design, tissue engineering, protein folding, and microfluidics. The goal for these endeavors is to mimic the "smartness" of biological systems and ultimately moderate complex systems such as immune responses at desired levels. The versatility and untapped potential of smart polymeric materials makes them one of the most exciting interfaces of chemistry and biology.     

Transparent ceramics from sol–gel derived elpasolites by cold pressing

A new method to produce ceramics transparent in the visible range from sol–gel derived Al-elpasolites by cold pressing is presented and the pressure-induced changes in the samples are described by scanning electron microscopy and powder X-ray diffraction. The described results are unique in the area of metal fluorides and offer new possibilities in materials science and especially in optics, as this approach is transferable to numerous other systems.     

Advanced energetic materials: novel strategies and versatile applications

Novel efficient synthetic strategies, including green methodologies, to basic and perspective high-energy density compounds, bearing active oxygen sources (C-, N- and O-nitro groups and N-oxide fragments) and high-enthalpy polynitrogen heterocycles, are briefly overviewed. Recently developed synthetic approaches to nitro group-free hypergolic ionic liquids (HILs) and strained 1,5-diaza- bicyclo[3.1.0]hexane derivatives capable of ultrafast ignition upon mixing with an oxidizer, and to high-energy liquid hydrocarbons with strained cyclopropane fragments are also considered. Physicochemical properties, energetic performances and potential applications of energetic compounds and composites as key components of explosives, powders and solid or liquid rocket propellants are critically discussed with a focus on original reports published in the period 2016–2021.     

Transparent oxyfluoride glass ceramics co-doped with Er and Yb - Crystallization and upconversion spectroscopy

Transparent glass ceramics in the system SiO₂-B₂O₃-PbO-CdO-PbF₂-CdF₂-YbF₃-ErF₃ showing infrared to visible anti-Stokes (upconversion) luminescence are studied in the present work. The glass compositions have been optimized in order to reduce the melting temperature and, hence, to obtain laboratory scale samples with good optical quality. Erbium-doped nanoscale Pb₄Yb₃F₁₇ crystals are precipitated in the precursor glasses during annealing at temperatures 30-40 K above T_g. A kinetically self-constrained growth explains the nano sizes of the crystals. Both the Stokes and anti-Stokes luminescence spectra of glasses could be explained with clustering of the Yb³⁺ and Er³⁺ ions in fluorine-rich regions. At the annealing temperature these regions act as nucleation precursors. The crystal growth further enhances the local concentration of these ions. Consequently, a series of energy transfer and energy cross relaxation processes occurs between adjacent rare earth ions leading to the observed luminescence spectra of the glass ceramics studied.     

A state-of-the-art review on particulate wood polymer composites: Processing,properties and applications

In the present decade, the demands for recyclable, environmentally friendly and low-cost with good strength composites materials have been significantly increased. In this context, the particulate wood polymer composites have attracted the researchers owing to their eco-friendliness, low-cost as they are prepared using waste wood particles, and good mechanical and physical properties. These composites were prepared by filling the waste wood particles into the polymers using different fabrication methods such as extrusion, hand layup, compression moulding, injection moulding and additive manufacturing (3D printing). A good number of research works have been reported on the testing and characterization of wood composites for the various applications so far. This fact motivated to prepare a state-of-the-art review on the recent developments in processing, characterization, and applications of wood composites. This paper presents a discussion on the chemical structure and properties of different types of wood species. The mechanical, thermal and water absorption behaviour of thermosets, thermoplastics and biopolymers based wood composites have also been discussed. Further, characterization of the nano biocomposites prepared using nanocellulose/nanoparticles of wood are also presented. The outcomes of the present review provide a good understanding of wood composites that will encourage the researchers for further research works & developments of novel wood composites for the advanced applications.     

Dendritic macromers for hydrogel formation: Tailored materials for ophthalmic,orthopedic, and biotech applications

Dendritic macromolecules are well‐defined highly branched macromolecules synthesized via a divergent or convergent approach. A salient feature of the macromolecules described herein, and a goal of our research effort, is to prepare dendritic macromolecules suitable for in vitro and in vivo use by focusing on biocompatible building blocks and biodegradable linkages. These dendritic macromolecules can be subsequently crosslinked to form hydrogels using a photochemical acrylate‐based or a chemical ligation strategy. The properties—mechanical, swelling, degradation, and so forth—of the hydrogels can be tuned by altering the composition, crosslinking chemistry, wt %, generation number and so forth. The utility and diverse applicability is demonstrated through successful use of these hydrogels in three unique applications: hydrogel adhesives for repairing corneal wounds, hydrogel scaffolds for cartilage tissue engineering, and hydrogel reaction chambers for high throughput screening of molecular recognition events. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 383–400, 2008.