Synthetic Opals Research Articles

Achieving Color and Function with Structure: Optical and Catalytic Support Properties of ZrO2 Inverse Opal Thin Films.

Taking inspiration from natural photonic crystal architectures, we report herein the successful fabrication of zirconia inverse opal (ZrO2 IO) thin-film photonic crystals possessing striking iridescence at visible wavelengths. Poly(methyl methacrylate) (PMMA) colloidal crystal thin films (synthetic opals) were first deposited on glass microscope slides, after which the interstitial voids in the films were filled with a Zr(IV) sol. Controlled calcination of the resulting composite films yielded iridescent ZrO2 IO thin films with pseudo photonic band gaps (PBGs) along the surface normal at visible wavelengths. The PBG position was dependent on the macropore diameter (D) in the inverse opals (and thus proportional to the diameter of the PMMA colloids in the sacrificial templates), the incident angle of light with respect to the surface normal (θ), and also the refractive index of the medium filling the macropores, all of which were accurately described by a modified Bragg’s law expression. Au/ZrO2 IO catalysts prepared using the ZrO2 IO films demonstrated outstanding performance for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4, which can be attributed to the interconnected macroporosity in the films, which afforded a high Au nanoparticle dispersion and also facile diffusion of 4-nitrophenol to the catalytically active Au sites.

Opal Adsorbs and Stabilizes RNA – A Hierarchy of Prebiotic Silica Minerals

A widely held ‘RNA first’ model proposes that RNA gave organic matter on Earth its first access to Darwinism. Such a proposal, which requires a mechanism to generate RNA from a prebiotic ‘soup’, must also manage the intrinsic instability of any RNA so formed. Here, we show that silicon dioxide (silica, SiO2), in the form of synthetic opal, adsorbs and stabilizes RNA from aqueous solution. The extent of adsorption on fully amorphous silica is less, as is the extent of adsorption on the surface of crystalline quartz. We show that the RNA adsorbed on opal is considerably more stable than the same RNA molecule free in aqueous solution at pH 9.5. This provides a mechanism by which any RNA formed in a prebiotic environment could have been concentrated and stabilized so that it could have later participated in the first Darwinian biology.

Heavy oil oxidation in the nano-porous medium of synthetic opal.

Increasing interest to study hydrocarbon behavior in fine porous media, awakened by the shale revolution, requires the application of suitable model porous media. In the current study we prepared nano-porous synthetic opal, profoundly investigated its morphological and textural properties, and studied the kinetics of combustion of heavy oil impregnated into nanopores. Comparison of kinetic parameters of the oil oxidation process for nano-porous and coarse-porous media revealed that nanoconfinement affects the reactivity of oil.

Multimode theory of plasmon excitation at a metal – photonic crystal interface

Surface plasmon excitation at a photonic crystal – metal interface is studied taking into account multiple scattering of an initial light wave on a periodical crystal structure. The analysis is focused on calculating characteristics of the eigenwaves in a one-dimensional crystal, which comprise a set of harmonics with the wavevectors separated from each other by the value of the crystal lattice wavevector. Reflection from the crystal – metal interface binds the amplitudes of propagating and evanescent modes. Calculations show that for the dielectric characteristics of a synthetic opal and a substrate made of a real metal with a ruby laser radiation used as the initial wave, the fulfilment of plasmon resonance conditions leads to a local increase in the surface plasmon amplitude by a factor of 6.4 – 9 as compared to the average amplitude of the initial wave. As a rule, the effect can only be obtained for a single surface wave, all other waves being substantially weaker than the main plasmon. There is a specific case where the resonance condition holds for two modes simultaneously. In this case, two oppositely directed fluxes of equal intensity are generated at the interface. The resonance condition breaks at a small deviation of the incident angle of the initial wave θ from the normal direction (|θ| ⩾ 10−4 rad). In the latter case, the picture is asymmetric: at angles |θ| ⩾ 5 × 10−3 rad, only one plasmon remains intensive. The local density of electromagnetic energy at the photonic crystal – metal interface may exceed the corresponding value of the initial wave by a factor of 40 – 80.

Phase transformations in opals under thermal and thermobaric actions

The ultrasmall- and wide-angle neutron diffraction methods are used to study multiscale structures and phase transformations in synthetic opals at different temperatures and pressures (as high as 1500°C and 10 GPa, respectively). Monodisperse colloidal particles of amorphous silica dioxide (a-SiO2) with an average diameter of 150‒1700 nm whose deviation from the mean is less than 5% are synthesized to fabricate the samples. Opal matrices up to 3 cm thick are obtained via the natural sedimentation of a SiO2-globule suspension followed by drying and heat treatment. Neutron-diffraction processes are investigated using a DISK multidetector superposition diffractometer mounted at the IR-8 reactor of the National Research Centre Kurchatov Institute at a neutron wavelength of 1.668 A. Ultrasmall-angle diffraction experiments are performed in the two-crystal mode of a STOIK spectrometer.

PA15 人工オパールに浸透させた液晶の光第二高調波発生(物理・物性)

PA15 人工オパールに浸透させた液晶の光第二高調波発生(物理・物性)

Formation of three-dimensional arrays of magnetic clusters NiO, Co3O4, and NiCo2O4 by the matrix method

A method has been proposed for the formation of three-dimensional arrays of isolated magnetic clusters NiO, Co3O4, and NiCo2O4 in the sublattice of pores in the matrix of bulk synthetic opals through a single impregnation of the pores with melts of nickel and cobalt nitrate crystal hydrates and their thermal degradation. The method makes it possible to controllably vary the degree of filling of pores in the matrix with oxides within 10–70 vol %. The composition and structure of the synthesized materials, as well as the dependences of their static magnetic susceptibility on the magnetic field strength, have been investigated.

Peculiarities of the irisation in precious opals in view of their mosaic–cluster (frustumation) inner fabric

A direct correlation was shown for the first time between mosaic irisation patterns in synthetic and natural precious opals (from Australia, Ethiopia, Honduras, Slovakia, and Russia) and their frustumational (lump or mosaic–cluster) inner structure by means of photoluminescence, X-ray phase analysis, IR and Raman spectroscopy, and scanning electron microscopy.

Efficiency of surface plasmon excitation at the photonic crystal – metal interface

We report the results of a theoretical investigation of light wave transformation in a one-dimensional photonic crystal. The scheme considered comprises an incident wave directed in parallel with layers of the photonic crystal under an assumption that the wave vector is far from a forbidden zone. Expressions for propagating and evanescent electromagnetic waves in a periodic medium of the photonic crystal are obtained. It is found that the transverse structure of the propagating wave comprises a strong constant component and a weak oscillating component with a period determined by that of the photonic crystal. On the contrary, the dependence of evanescent waves on transverse coordinates is presented by a strong oscillating component and a weak constant component. The process of transformation of propagating waves to evanescent waves at a crystal – metal interface is investigated. Parameters of the photonic crystal typical for synthetic opals are used in all numerical simulations. The theoretical approach elaborated yields in an explicit form the dependence of the amplitude of a generated surface wave on the period of the dielectric function modulation in the photonic crystal. The results obtained show that in the conditions close to plasmon resonance the amplitude of the surface wave may be on the order of or even exceed that of the initial incident wave.

Angle-dependent luminescence and reflection spectra of synthetic opal

We have studied the influence of the first- and second-order stop bands on the luminescence and reflection spectra of synthetic opal (SiO2) photonic crystals in the visible range. It has been shown that the position of the photonic stop bands in the luminescence and reflection spectra of opal depends on light propagation direction. Using optical measurements, we have determined important parameters of the photonic crystals, such as their refractive index and the diameter of the opal spheres. We have found that the effect of a photonic crystal on the visible emission intensity is much stronger in the first photonic bandgap of opal than in the second.

Control over the distribution of luminescent impurities inside opal photonic crystals

The work is focused on the problem of control over the distribution of emitting centers inside photonic crystals. Two ways of luminescent impurity incorporation into synthetic silica opals are considered. First is based on the infiltration of the opal with a water solution of organic complexes (HEuEDTA) and leads to a formation of a uniform luminescent layer on the surface of silica microspheres. The other involves the infiltration of the structure with a heptane solution of CdSe quantum dots leading to the localization of the luminescent component around contact points between microspheres. Thus two different types of strongly ordered distribution of luminescent component inside opal can be obtained. Corresponding samples were prepared and their optical properties are discussed.

Nanocrystalline mimetic opals: synthesis and comparative characterization vs. natural stones

<p>The objective of this project was to synthesis and to comparative characterization of nanocrystalline opals. Synthesis technique called Stöber allows obtaining nano and micro particles monodisperse. Natural opal of origin Mexican was utilized as reference. The results obtained indicated crystalline phases in the opal, and the presence of water is shown through x-ray diffraction and the FTIR and Raman spectra, respectively. Scanning electron microscopy illustrated spherical nanoparticle of silicon. We conclude that the synthetic opal presents a mimetic character.</p>

Luminescence response of synthetic opal under femtosecond laser pumping

Synthetic opal is an artificial photonic metamaterial composed from spherical globules of amorphous silica (SiO2) about 300nm in diameter. We report, for the first time to our knowledge, the origin of a narrow luminescence spectral peak (4nm HWHM) and optical second and third harmonic generation in synthetic opal samples under femtosecond laser excitation (800nm) at liquid-nitrogen temperature. Stimulated-emission effects are discussed related to the possibility of nanocavity lasing at the condition of the first Mie resonance in a dielectric sphere.

Nonlinear optical conversion in synthetic opal

This paper presents an experimental study of third optical harmonic generation processes in synthetic opal. Excitation was provided by ultrashort (∼10−13 s) laser pulses (λ = 1026 and 513 nm) with a high repetition rate (105 Hz), high peak power (up to 1 GW), and low pulse energy (10−5 J). The third optical harmonic intensity was shown to depend significantly on the diameter of the silica spheres, which determines the spectral position of the band gaps in the opal photonic crystal. The highest efficiency of the nonlinear optical conversion of excitation light to the third optical harmonic was observed when the excitation or optical harmonic wavelength was close to the spectral position of the band gap of the photonic crystal. This behavior can be accounted for by the presence of surface photon (Tamm) states of the optical field in opal photonic crystals in the spectral region corresponding to the band gap of the photonic crystal. The presence of photon Tamm states leads to the formation of high spectral intensity regions localized near the surface of the photonic crystal. This causes a considerable increase in nonlinear optical conversion efficiency, in particular, in the case of the third optical harmonic generation in the centrosymmetric structure of opal lattices.

Band Structure of Photonic Crystals Fabricated by Two-Photon Polymerization

We study theoretically the band-gap structures of several types of three-dimensional photonic crystals with the fcc lattice symmetry: synthetic opals, inverted yablonovite and woodpile. The samples of inverted yablonovite, inverted yablonovite with a glassy superstructure and woodpile are fabricated by two-photon polymerization through a direct laser writing technique, which allows the creation of complex three-dimensional photonic crystals with a resolution better than 100 nm. A material is polymerized along the trace of a moving laser focus, thus enabling the fabrication of any desirable three-dimensional structure by direct “recording” into the volume of a photosensitive material. The correspondence of the structures of the fabricated samples to the expected fcc lattices is confirmed by scanning electron microscopy. We discuss theoretically how the complete photonic band-gap is modified by structural and dielectric parameters. We demonstrate that the photonic properties of opal and yablonovite are opposite: the complete photonic band gap appears in the inverted opal, and direct yablonovite is absent in direct opal and inverted yablonovite.

Study of the structure of synthetic opals affected by temperature and pressure

It is demonstrated that synthetic opals, like most natural ones, have a cristobalite rather than quartz basis, change their color from white to blue after losing their water-containing component, and form superlattices. Being affected by temperature and pressure, they undergo partial or complete crystallization to the corresponding polymorphic modifications.

The influence of structural defects on the optical properties of synthetic opals

The influence of structural defects on the optical properties of synthetic opals

Stimulated light scattering in synthetic opal filled with dielectrics

We have studied characteristics of stimulated light scattering in synthetic opal crystals made up of silica spheres. This type of light scattering results from interaction between pulsed laser radiation and dielectric nanoparticles, such as silica (SiO2) spheres in the structure of synthetic opal. The Stokes shift in the scattered radiation spectrum was 0.4–1.0 cm−1. The Stokes shift was determined as a function of scattering geometry, sphere diameter, sample temperature, and the type of dielectric in the opal pores. The results are of interest for assessing the size of nanoparticles in spatially ordered inorganic structures.

Chemical vapor deposition of isolated spherical diamond particles with embedded silicon-vacancy color centers onto the surface of synthetic opal

Isolated spherical diamond particles with embedded silicon-vacancy color centers are synthesized on a patterned surface of synthetic opal by chemical vapor deposition methods. The phase composition of the particles is determined and their structural and luminescence properties are studied. Prospects are discussed for the application of these particles as integrated spherical diamond microcavities, in which color centers are situated directly in the microcavities.

Multiple Bragg diffraction in opal-based photonic crystals: Spectral and spatial dispersion

We present an experimental and theoretical study of multiple Bragg diffraction from synthetic opals. An original setup permits us to overcome the problem of the total internal light reflection in an opal film and to investigate the diffraction from both the $(111)$ and $(\overline{1}11)$ systems of planes responsible for the effect. As a result, angle- and frequency-resolved diffraction and transmission measurements create a picture of multiple Bragg diffraction that includes general agreement between dips in the transmission spectra and diffraction peaks for each incident white light angle and a twin-peak structure at frequencies of the photonic stop band edges. Two opposite cases of the interference are discussed: an interference of two narrow Bragg bands that leads to multiple Bragg diffraction with anticrossing regime for dispersion photonic branches and an interference of a narrow Bragg band and broad disorder-induced Mie background that results in a Fano resonance. A good quantitative agreement between the experimental data and calculated photonic band structure has been obtained.