Synthetic Opals Research Articles

Radiation-Induced Paramagnetic Centers in Meso- and Macroporous Synthetic Opals from EPR and ENDOR Data

The paramagnetic defects and radiation-induced paramagnetic centers (PCs) in silica opals can play a crucial role in determining the magnetic and electronic behavior of materials and serve as local probes of their electronic structure. Systematic investigations of paramagnetic defects are essential for advancing both theoretical and practical aspects of material science. A series of silica opal samples with different geometrical parameters were synthesized and radiation-induced PCs were investigated by means of the conventional and pulsed X- and W-band electron paramagnetic resonance, and 1H/2H Mims electron-nuclear double resonance. Two groups of PCs were distinguished based on their spectroscopic parameters, electron relaxation characteristics, temperature and time stability, localization relative to the surface of silica spheres, and their origin. The obtained data demonstrate that stable radiation-induced E’ PCs can be used as sensitive probes for the hydrogen-containing fillers of the opal pores, for the development of compact radiation monitoring equipment, and for quantum technologies.

Extending Polymer Opal Structural Color Properties into the Near-Infrared

We report the fabrication and characterisation of near-IR reflecting films and coatings based on shear-assembled crystalline ensembles of polymer composite microspheres, also known as “polymer opals”. Extension of the emulsion polymerisation techniques for synthesis of tractable larger core-interlayer-shell (CIS) particles, of up to half a micron diameter, facilitates the engineering and processing of thin-film synthetic opals, with a tunable photonic stopband spanning an extended spectral range of λ ≈ 700–1600 nm. Samples exhibit strong “scattering cone” interactions, with considerable angular dependence and angle tuning possible, as measured with a goniometric technique. These intense optical resonances in the near-IR, particularly within the important region around λ ~ 800 nm, combined with an appreciable translucency within the visible light spectrum, is indicative of the potential applications in coatings technologies and solar cells.

LIBS Efficiency Increase via Plasmonic Nanoparticles in the Study of Synthetic Opal Matrices

LIBS Efficiency Increase via Plasmonic Nanoparticles in the Study of Synthetic Opal Matrices

Characterization of synthetic opals filled with copper

Photonic crystals based on synthetic opals filled with copper were produced by using the electrochemical deposition technique. Copper nanocrystal formation together with some quantity of their oxides inside opal pores was proved by the X-ray diffraction pattern. An angular behavior of reflectance maximum for opals with different copper content was satisfactorily described in the framework of theBragg light diffraction model. Effective dielectric constant of the opal-copper structures was determined.

Synthetic Opals or Versatile Nanotools-A One-Step Synthesis of Uniform Spherical Silica Particles.

Synthetic opals, a composition of homogeneous silica spheres in the mesoscale size range, have attracted the attention of scientists due to their favorable chemical and physical properties. Their chemical inertness and stability, biocompatibility, homogeneity, elevated specific surface area, and ease of functionalization of their surfaces make them a versatile nanotool. In the present study, the Stöber process was used to investigate the effect of parameters, such as reagent concentration and synthesis temperature, on the resulting silica particle size and structure. The optimal conditions for successfully obtaining homogeneous particles in the mesoscale range with high reproducibility were investigated. Several synthesis procedures and their dependence on the reaction temperature were presented to allow the selection of the assumed diameter of silica spheres. The numerous samples obtained were examined for size, homogeneity, structure, and specific surface area. On the basis of specific surface area measurements and nuclear magnetic resonance studies, the internal hierarchical structure of the spherical silica was confirmed as consisting of a solid core and layers of secondary spheres covered by a solid shell. Structural studies (X-ray Spectroscopy, X-ray Absorption Near-Edge Structure, and nuclear magnetic resonance), together with infrared vibrational spectroscopy, showed no dependence of the structure of the obtained mesospheres on the concentration of reagents and the size of the obtained particles.

Effect of the Pore Structure of Nanosilicas Decorated with Cobalt and Cerium Oxides on Catalytic Activity in the Selective Oxidation of Carbon Monoxide

Two types of nanosilicas with different pore structures are synthesized and decorated via impregnation with cobalt and cerium oxides. Meso–microporous spherical silica particles with thin walls of SiO2 nanochannels having specific surface area and pore volume of up to 1400 m2/g and 0.8 cm3/g, respectively, are used. Macroporous three-dimensionally ordered structures based on SiO2 (so-called synthetic opals) consisting of close-packed submicron spherical silica particles with respective porosity characteristics of 11 m2/g and 0.2 cm3/g are also used. The synthesized materials are characterized via low-temperature nitrogen adsorption, X-ray diffraction, SEM, XPS, and Fourier transform IR spectroscopy, and tested as catalysts for the selective oxidation of CO in excess H2 (CO-PROX). The effect of silica, the ratio of introduced oxides, and the order of their introduction on the structure and catalytic properties of Co–Ce/SiO2 are revealed. The catalytic behavior of the synthesized materials is determined from the specificity of interactions among the metal oxides and with the silica surface.

Synthetic Opals in Laser-Induced Breakdown Spectroscopy Problems

Synthetic Opals in Laser-Induced Breakdown Spectroscopy Problems

Shortwave UV Blue Luminescence of Some Minerals and Gems Due to Titanate Groups

This article reviews blue shortwave-excited luminescence (BSL) in natural minerals and synthetic materials. It also describes in detail the emission of seven minerals and gems displaying BSL, as well as three references in which BSL is caused by titanate groups (TiO6): benitoite, Ti-doped synthetic sapphire and spinel. Emission (under 254 nm shortwave excitation) and excitation spectra are provided, and fluorescence decay times are measured. It is proposed that BSL in beryl (morganite), dumortierite, hydrozincite, pezzotaite, tourmaline (elbaite), some silicates glasses, and synthetic opals is due to titanate groups present at a concentration of 20 ppmw Ti or above. They all share a broad emission with a maximum between 420 and 480 nm (2.95 to 2.58 eV) (thus perceived as blue), and an excitation spectrum peaking in the short-wave range, between 230 and 290 nm (5.39 to 4.27 eV). Furthermore, their luminescence decay time is about 20 microseconds (from 2 to 40). These three parameters are consistent with a titanate emission, and to our knowledge, no other activator.

Application of silica opals to ceramic pottery

ABSTRACT This paper reports the first study on using synthetic silica opals to make ceramic pottery with structural colors. The silica opals were adhered to the pottery substrate by heating at 900°C with a glass phase connecting them. The influence of the heating on the color appearance of the silica opals was investigated in depth. In the study, they were successfully adhered to the pottery substrate with no additives by using the silica opals synthesized with a small amount of catalyst reagent. This finding allows us to control iridescent/non-iridescent coloring of the silica. Additionally, we found unique color changes when the product was wetted. The detailed strategies provided in this paper for synthesizing of silica opals, coating, and heating on pottery are expected to offer useful references for the applications in the field of ceramic art.

Mechanochromic and Thermochromic Sensors Based on Graphene Infused Polymer Opals.

High quality opal‐like photonic crystals containing graphene are fabricated using evaporation‐driven self‐assembly of soft polymer colloids. A miniscule amount of pristine graphene within a colloidal crystal lattice results in the formation of colloidal crystals with a strong angle‐dependent structural color and a stop band that can be reversibly shifted across the visible spectrum. The crystals can be mechanically deformed or can reversibly change color as a function of their temperature, hence their sensitive mechanochromic and thermochromic response make them attractive candidates for a wide range of visual sensing applications. In particular, it is shown that the crystals are excellent candidates for visual strain sensors or integrated time‐temperature indicators which act over large temperature windows. Given the versatility of these crystals, this method represents a simple, inexpensive, and scalable approach to produce multifunctional graphene infused synthetic opals and opens up exciting applications for novel solution‐processable nanomaterial based photonics.

Core-shell silica-rhodamine B nanosphere for synthetic opals: from fluorescence spectral redistribution to sensing.

Photonic crystals are a unique tool to modify the photoluminescence of light-emitting materials. A variety of optical effects have been demonstrated by infiltrating opaline structures with photoactive media. On the other hand, the fabrication of such structures includes complex infiltration steps, that often affect the opal lattice and decrease the efficiency of light emission control. In this work, silica nanospheres were directly functionalized with rhodamine B to create an emitting shell around the dielectric core. Simple tuning of the microsphere preparation conditions allows selecting the appropriate sphere diameter and polydispersity index approaching 5%. These characteristics allow facile self-assembling of the nanospheres into three-dimensional photonic crystals whose peculiar density of photonic states at the band-gap edges induces spectral redistribution of the rhodamine B photoluminescence. The possibility to employ the new stable structure as sensor is also investigated. As a proof of principle, we report the variation of light emission obtained by exposure of the opal to vapor of chlorobenzene.

Synthesis and Structural Properties of Nanocomposites Based on Synthetic Opals and Active Dielectrics

This work is devoted to generalize and analyze the previouse results of new photonic-crystalline nanomaterials based on synthetic opals and active dielectrics. Data were characterized by X-ray diffraction and Raman spectroscopy. Active dielectrics infiltrated into the pores of the opal from the melt. The phase structure composition of the infiltrated materials into the pores of the opal matrix were analyzed. The results of x-ray diffraction and Raman spectra allowed to establish the crystal state of active dielectrics in the pores of the opal. The Raman spectra of some opal-active dielectric nanocomposites revealed new bands and changes in band intensities compared to the spectra of single crystals of active dielectrics. Further more, differences in band intensities in the spectra were measured at different spots of the sample‘s surface were observed. The revealed changes were attributed to the formation of new crystalline phases due to the injected dielectrics in opal pores.

Irreversible phase transitions in structural elements of synthetic opal

The globular photonic crystal of artificial opal was synthesized by Stœber process in order to study its internal structure. Two methods were used to measure density and to determine porosity, which was 0.368. A fractal model of pores formation was considered for different silica phases, including the amorphous one. Assumptions were made on the type of pores inside globules. The differential scanning calorimetry method was used to reveal the fine multisection structure of the heat flow thermogram through the sample. The second-order phase transition was revealed. The experimental substantiation was given that phase transition is connected with the creation of β-cristobalite. A model was proposed for calculation of the number of component molecules leaving a sample at heating. Independent confirmation of calculation as per the proposed model was obtained by the gravimetric analysis.

Synthesis and Photocatalytic Properties of Tantalum Nitride with an Inverse Opal Structure

Certain oxynitrides (LaTiO2N and TaON) and nitrides (Ta3N5) demonstrate potential as visible-light-driven photocatalysts1. These materials are typically synthesized from oxide precursors by thermal ammonolysis at temperatures up to 950 oC. Accordingly, these oxynitrides and nitrides intrinsically possess an abundance of anion vacancies or defects which act as electron-hole pair recombination centers, thereby limiting photocatalytic performance. In this work, we introduce photonic band gap engineering as a strategy for suppressing electron-hole pair recombination in tantalum nitride thin films, thereby achieving improved photocatalytic performance. Briefly, a series of inverse opal (IO) Ta3N5 thin films with different macropore sizes were fabricated by the colloidal crystal template approach. This kind of approach has been successfully made on TiO2 photocatalysts2. Three batches of monodisperse polymethylmethacrylate (PMMA) colloids of diameters ranging from 230 to 430 nm were first synthesized by the surfactant-free emulsion polymerization of methyl methacrylate. PMMA colloidal crystal thin films were then grown on silica glass slides using a flow-controlled vertical deposition technique. As the meniscus of the suspension moved down the glass slide by pumping up a peristaltic pump, colloidal crystal layer of several microns were deposited. Several drops of TaCl5 solution were placed softly on the edge of the colloidal crystal and immersed into the crystal by capillary phenomena. Subsequently, the interstitial voids in the colloidal crystal films (synthetic opals) were filled with a tantalum hydroxide sol. Ammonolysis of the resulting composite films under an ammonia stream of 200 ml/min at 700ºC yielded IO Ta3N5 thin films, shown in Fig.1. The IO Ta3N5 films possess a 3-dimensionally ordered macroporous structure with periodicity on the scale of visible-light wavelengths, resulting in pseudo photonic band gaps at visible wavelengths. By matching the red-edge of the PBG location with the absorption edge of Ta3N5, electron-hole pair recombination is suppressed and the photocatalytic activity dramatically improved. In this experiment, strong reflection due to [111] photonic bandgap was clearly observed at 543nm for the IO amorphous Ta2O5 film and at 581nm for the IO Ta3N5 film, respectively. Appearance of the IO Ta3N5 film was reddish orange in color but it gave a strong yellow reflection in a certain angle, seen in Fig. 2. Since the optical bandgap of Ta3N5 was estimated to be 2.1eV (=590nm), the IO tantalum nitrides with both optical and bandgaps properly matched could be fabricated. Photocatalystic H2 evolution activity of the IO Ta3N5 under UV or visible ray irradiation will be appeared at the presentation, togather with a comparison with that of Ta3N5 powder. References Tsuyoshi Takata, Chengsi Pan and Kazunari Domen; Sci. Technol. Adv. Mater., 16 (2015) 033506 (18pp).Waterhouse et al., Sci. Rep., 3 (2013) 2849 (5pp). Figure 1

Transparency induced in opals via nanometer thick conformal coating

Self-assembled periodic structures out of monodisperse spherical particles, so-called opals, are a versatile approach to obtain 3D photonic crystals. We show that a thin conformal coating of only several nanometers can completely alter the reflection properties of such an opal. Specifically, a coating with a refractive index larger than that of the spherical particles can eliminate the first photonic band gap of opals. To explain this non-intuitive effect, where a nm-scaled coating results in a drastic change of optical properties at wavelengths a hundred times bigger, we split the permittivity distribution of the opal into a lattice function convoluted with that of core-shell particles as a motif. In reciprocal space, the Bragg peaks that define the first Brillouin zone can be eliminated if the motif function, which is multiplied, assumes zero at the Bragg peak positions. Therefore, we designed a non-monotonic refractive index distribution from the center of the particle through the shell into the background and adjusted the coating thickness. The theory is supported by simulations and experiments that a nanometer thin TiO2 coating via atomic layer deposition (ALD) on synthetic opals made from polystyrene particles induces nearly full transparency at a wavelength range where the uncoated opal strongly reflects. This effect paves the way for sensing applications such as monitoring the thicknesses growth in ALD in-situ and in real time as well as measuring a refractive index change without spectral interrogation.

Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Inclusions in Natural, Treated, Synthetic, and Imitation Opal

Fabrication and characterization of crystalline Bi2TeO5 - Bi4Si3O12 - SiO2 nanocomposite

The matrix nanocomposite described here is fabricated using a reactive melt infiltration process exploiting crystalline bismuth tellurite (Bi2TeO5) powder and porous silica dioxide (SiO2) matrix as original components. The original matrix, that is composed of regularly arranged amorphous SiO2 spheres, and is known as synthetic opal, reacts with the molten Bi2TeO5, forming three components (Bi2TeO5, bismuth orthosilicate (Bi4Si3O12), and $ \alpha$ -cristobalite) when cooled down to room temperature. The first two components can be considered as a set of nanocrystals with an average linear size more than 30nm and lattice parameters changed in comparison with those in a single crystal lattice. The $ \alpha$ -cristobalite component is formed rather as a network at the sites of amorphous SiO2 spheres whose presence in the obtained composite is not detected. A dominant role of bismuth ions in breaking the Si-O-Si bonds in a bridge-like structure of amorphous SiO2 spheres is proposed.

Probing the surface of synthetic opals with the vanadyl containing crude oil by using EPR and ENDOR techniques

Probing the surface of synthetic opals with the vanadyl containing crude oil by using EPR and ENDOR techniques

Raman Scattering in Nanocomposites Based on Synthetic Opal and Nanocrystalline Bi2TeO5

This paper presents a systematic Raman scattering study of novel nanostructured materials based on synthetic opal and Bi2TeO5 nanocrystals, which offer high photorefractive sensitivity. Bismuth tellurite was introduced into opal pores in a molten state. The crystal structure of the material in the opal pores was determined by Raman spectroscopy. Comparison of the measured Raman spectra of the opal–Bi2TeO5 nanocomposite and those of polycrystalline powders and single crystals made it possible to reveal a number of new bands and analyze their origin. The observed variation in the intensity of Raman bands from point to point on the sample surface can be interpreted as due to structural light focusing and excitation field localization at surface and volume defects of the photonic crystal structure of the material.

Different regimes of the Purcell effect in disordered photonic crystals

We demonstrate that disorder in photonic crystals could lead to pronounced modification of spontaneous emission rate in the frequency region corresponding to the photonic band gap (PBG). Depending on the amount of disorder, two different regimes of the Purcell effect occurs. We provide statistical analysis of Purcell coefficient on the frequency of the emitter and its position within the sample. For the moderate disorder, an enhancement of spontaneous emission occurs at the edge of PBG due to the modification of properties of the edge state. This effect is responsible for recently observed mirrorless lasing in photonic crystals at the edge of PBG. When the level of disorder increases, the spontaneous emission rate enhances within the PBG due to the appearance of the high quality factor states. This effect is likely responsible for a superlinear dependence of emissions on pumping observed in synthetic opals.