Active Optical Materials Research Articles

Morphological and topological analysis of coarsened nanoporous gold by x-ray nanotomography

Nanoporous gold has numerous potential applications 1 in optical-active materials, catalysts, sensors, mechanical actuators, fuel cell and microbalance electrodes, and as a coating for medical devices. Nanoporous gold is fabricated by dealloying silver-gold solid solutions. This results in fully openporosity bicontinuous nanoporous structures, following the rearrangement of the gold atoms into interconnected ligaments as the silver atoms are selectively removed. 2 Optimization of the optical, chemical, and mechanical properties of nanoporous gold depends on its pore size, which is tunable by structural coarsening during annealing. 3 Various electronbased techniques have been employed to determine the morphology of nanoporous gold films after dealloying, but none are suited to three-dimensional 3D study of thick specimens of coarsened nanoporous gold. Tomographic transmission electron microscopy provides very high spatial resolution but is limited to examining thin films, and cannot image coarsened structures once the gold ligament size is close to the electron penetration depth. 4,5 Focused ion beam FIB-scanning electron microscopy serial sectioning 6 combines high resolution with depth penetration, however, being a destructive method, it cannot be used to observe dynamic processes and structural evolution in 3D. X-ray microcomputed tomography is a powerful nondestructive tomographic tool whose resolution is however typically limited to the micron scale. 7 Transmission x-ray microscopy TXM using synchrotron x-ray sources offers 30 nm resolution, fast image acquisition, and the ability to nondestructively image samples tens of microns thick. Combining TXM with tomographic methods allows complex nanostructures to be imaged in 3D. 8 Here, we perform x-ray nanotomography on a dealloyed and coarsened nanoporous gold wire. We quantitatively analyze the morphological and topological properties of nanoporous gold from the reconstructed images using methods developed in earlier work. 9

Effect of Polarized Light Emitting Diode Irradiation on Wound Healing

We propose a new phototherapy using polarized light from light emitting diode (LED). The purpose of this study is to clarify the effect of polarized LED irradiation on wound healing. Five groups were classified: control (C), unpolarized (U), linearly polarized (L), right circularly polarized (RC), and left circularly polarized (LC) LED irradiation. In vitro study, fibroblast cell cultures were irradiated, and cellular proliferation was evaluated with a WST-8 assay. In vivo study, full-thickness skin defect of 20 mm diameter was created on the dorsal side of rats. The ratio of the residual wound area was measured, and expression of type 1 and type 3 procollagen mRNA in granulation tissue was determined by real-time reverse transcription polymerase chain reaction method. The cellular proliferation rates of group RC and L were significantly higher than other groups. The ratio of the residual wound area of group RC and L was significantly reduced than group C and U. Expression of type 1 procollagen mRNA in group RC was found to be significantly increased about 1.5-fold in comparison with the group C. There were no significant differences for type 3 procollagen. The right circularly polarized light and linearly polarized light promoted the process of wound healing by increasing the proliferation of fibroblasts, and the right circularly polarized light increased the expression of type 1 procollagen mRNA. The effectiveness of right circularly polarized light suggests that some optical active material, which has a circular dichroic spectrum, takes part in a biochemical reaction.

Gain-assisted time delay of plasmons in coupled metal ring resonator waveguides

Coupled metal ring resonator waveguides filled with optical active materials are proposed to achieve the slow light and tunable time delay. The tunable group index and time delay are realized by the dispersion of the active materials and its interplay with that of the geometric structure of the waveguides. Our results from the transfer matrix analysis and finite-difference time-domain numerical simulation show that the anomalous dispersion of the active materials can help to amplify the group index determined by the waveguide geometry. Based upon this structure, a variable-bit-rate optical time-division-multiplexing system is numerically demonstrated.

Synthesis and Characterization of Nanoparticles of TiO2

ABSTRACTThe first steps in the synthesis of nanostructures are followed through UV-Vis and correlated with photoluminescence and images taken by SEM and TEM. Colloids permit the control in the atomic arrangement and the formation of nanostructures used to build cluster of materials. The size of the cluster in the colloid is around 5 nm. After the formation of the colloid a hydrothermal growth and microwave heating allows the formation of an ensemble of nano-sheet. This work is aim in the direction to controls the synthesis and the properties of materials with potential applications as active optical materials.

Nonlinear optical polyimides consisting of chromophore‐containing dendrons with site‐isolation effect

AbstractTo investigate the dendritic structure effects on the electro‐optical (EO) coefficients and thermal stability of the nonlinear optical (NLO) active materials, a bifunctional compound, IDD (4‐isocyanato‐4′(3,3‐dimethyl‐ 2,4‐dioxo‐acetidino)‐diphenylmethane) was used as a building block to synthesize a series of novel NLO chromophore‐containing dendritic structures including Generation 0.5 (G0.5) to Generation 3 (G3). The glass transition temperatures (Tg) of G1–G3 dendrons were in the range of 76–116°C, whereas only the G0.5 dendron exhibited a melting temperature (Tm), 98°C. Moreover, a series of NLO‐active guest–host systems ranging from polyimide‐G0.5 (PI‐G0.5) to polyimide‐G3 (PI‐G3) were prepared by blending 20 wt% chromophore‐containing dendron with a high Tg polyimide. EO coefficients ranged from 6.1 to 12.9 pm/V. The r33/dye content ratio increased with increasing generation of dendron‐containing polyimide samples. Particularly, the improvement in r33/dye content ratio of PI‐G2.5 sample tripled as compared to that of the guest–host sample with Disperse Red 1. Excellent temporal stability of PI‐G0.5 and PI‐G1.5 at 80°C was obtained. Moreover, waveguide properties for NLO polymers containing higher generation dendrons (3.1–3.6 dB/cm at 830 nm) were also obtained. Copyright © 2008 John Wiley & Sons, Ltd.

PUBLISHING ACS to launch new materials science journal

In early 2009, the American Chemical Society will introduce its 36th journal, ACS Applied Materials & Interfaces. Kirk S. Schanze, a chemistry professor at the University of Florida (UF), will serve as editor of the new publication. The peer-reviewed journal will be the first ACS materials chemistry publication to “focus exclusively on applied science and engineering, as opposed to fundamental science and engineering,” Schanze says. Its articles, letters, editorial commentaries, and topical forums will cover a range of subjects, including advanced active and passive electronic and optical materials, coatings, colloids, biomaterials and bio-interfaces, polymer materials, hybrid and composite materials, and friction and wear. “With nearly 10 years’ tenure as a senior editor for the ACS journal Langmuir , collaborations with government and industrial laboratories, and broad research interests that dovetail extremely well with the scope of the journal, professor Schanze was the natural candidate for editor-in...

Electronic polarizability and Judd–Ofelt parameters of Nd3+ and Er3+ ions in transparent crystallized glasses with nonlinear optical Ba2TiSi2O8 nanocrystals

Transparent crystallized glasses consisting of nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals are prepared in Eu(2)O(3)-, Nd(2)O(3)-, and Er(2)O(3)-doped 40BaO-20TiO(2)-40SiO(2) glasses by a conventional heat treatment method in order to clarify the optical properties of rare-earth (RE) ions in nanocrystals. The electronic polarizabilities of crystallized glasses are evaluated from the values of density and refractive index, and are found to decrease due to nanocrystallization, which indicates that the chemical bonding state in the crystallized glasses is more covalent compared to the precursor glasses. It is proposed from x-ray diffraction analyses and photoluminescence spectra of Eu(3+) ions that RE ions such as Nd(3+) and Eu(3+) are incorporated into Ba(2)TiSi(2)O(8) nanocrystals. The Judd-Ofelt parameters, Omega(t) (t=2, 4, and 6), of Nd(3+) and Er(3+) ions are evaluated from optical absorption spectra. It is observed that the Omega(2) parameter of Nd(3+) and Er(3+) increases largely due to nanocrystallization, suggesting that the site symmetry of Nd(3+) and Er(3+) ions in nanocrystallized glasses is largely distorted due to their incorporations into the Ba(2+) sites in Ba(2)TiSi(2)O(8) nanocrystals. The change in the Omega(4) and Omega(6) parameters due to nanocrystallization is small. It is proposed that nonlinear optical Ba(2)TiSi(2)O(8) nanocrystals including RE ions would have a high potential as active optical materials.

Controlling energy transfer between multiple dopants within a single nanoparticle

Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF3 nanoparticles doped with Tb3+ and Eu3+ and consisting of up to four layers were synthesized with an outer diameter of approximately 10 nm. It is found that by varying the thicknesses of an undoped layer between a Tb3+-doped layer and a Eu3+-doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm Tb3+ and 590 nm Eu3+ peaks was tailored from <0.2 to approximately 2.4 without changing the overall composition of the particles but only by changing the internal structure. Further, the emission spectrum of a blend of singly doped nanoparticles is shown to be equivalent to the spectra of co-doped particles when a core-shell configuration that restricts ET is used. Beyond simply controlling ET, which can be limiting when designing materials for optical applications, this approach can be used to obtain truly engineered spectral features from nanoparticles and composites made from them. Further, it allows for a single excitation source to yield multiple discrete emissions from numerous lanthanide dopants that heretofore would have been quenched in a more conventional active optical material.

Nanostructure designed powders of optical active materials MexSiOy obtained by ultrasonic spray pyrolysis

A new approach to the two-level design and self-assembling of MexSiOy (Me=Gd, Y and Ca or their mixtures) nano-powders from SiO2 sols is described. The nanostructure design of various optical active materials based on different compounds of MexSiOy is discussed. These particles were formed by the combination of hydrothermal synthesis and ultrasound spray pyrolysis. The morphology and structural design of the particles and sub-particles are defined by their synthesis procedure and processing parameters. The mean particle size and size distribution of all the MexSiOy based compounds were determined by SEM analysis. These results were compared with the particle diameter evaluated from the theoretical model of the breaking-up of capillary waves. For all the synthesized powders, the obtained results indicate the possibility of a rigorous design of the structure of the particles throughout their entire hierarchy.

Single semiconductor nanocrystals: Physics and applications

Semiconductor nanocrystals are nanoscale light sources that received much attention in recent years. We will give an overview about semiconductor colloidal nanocrystals as active optical materials in photonic structures and hybrid colloidal-epitaxial devices, for realizations of cavity quantum electrodynamics (cavity QED) concepts, or for probing field intensities in coupled resonator optical waveguides.

Electrically Tunable Silicon 2-D Photonic Bandgap Structures

Electrical tuning of high refractive index-contrast photonic bandgap (PBG) structures is required for a majority of PBG applications, particularly for integrated optics. When the host material is a semiconductor with poor electro-optical properties, tuning can be achieved by infiltrating the structure with an active optical material. In this paper we analyze the switching of electro-optic material in such structures, and suggest design rules to help achieve electrical tuning. In particular, a design concept that eliminates the electric field screening effects is proposed. The developed rules and concepts are demonstrated by the electrical tuning of liquid crystals inside two-dimensional porous silicon PBG structures. This approach can be generalized to different combinations of semiconductor PBG structures and active optical materials

SHG-Activity of Polar Nano-Structures of LC-RED-PEGM-7 Based Sono-Gel Hybrid Materials

The synthesis of sol-gel materials induced by ultrasonic action (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic and optical properties. A newly synthesized liquid crystalline mesogen (named here RED-PEGM-7) was introduced as dopant specie within the SiO2 matrix in order to create an active nonlinear optical hybrid material at room temperature. A comparative characterization of the structural properties between a pure reference sample and several doped composites was performed by X-ray diffraction (XRD) and atomic force microscopy (AFM); where, an optimal dissolution concentration of tetraethoxysilane (TEOS) and the liquid crystalline (LC) mesogen, to obtain good mechanical and nonlinear optical properties in thin film layers has been found.

DNA Photonics [Deoxyribonucleic Acid

ABSTRACT Purified deoxyribonucleic acid (DNA) derived from salmon and scallop sperm has demonstrated excellent passive and active optical properties. Characterization of the optical and electromagnetic properties of DNA suggests suitability for photonic applications. One of interesting features of DNA we discovered was an intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules. We found that various optical dyes inserted into the double helix of DNA molecules rendered active optical waveguide materials with excellent nonlinear optical properties. Our research included the investigation of DNA for use as an optical waveguide material as well as intercalation of fluorescent dyes, photochromic dyes, nonlinear optic chromophores, two photon dyes and rare earth compounds into DNA for use as a nonlinear optical material.

Hybrid Epitaxial−Colloidal Semiconductor Nanostructures

We present a growth technique which combines wet-chemical growth and molecular beam epitaxy (MBE) to create complex semiconductor nanostructures with nanocrystals as active optical material. The obtained results show that wet-chemically prepared semiconductor nanocrystals can be incorporated in an epitaxally grown crystalline cap layer. As an exemplary system we chose CdSe nanorods and CdSe(ZnS) core-shell nanocrystals in ZnSe and discuss the two limits of thin (d approximately 2R) and thick (d>2R) ZnSe cap layers of thickness d for CdSe nanorods and nanodots of radii R between 2 and 4 nm. In contrast to the strain-induced CdSe/ZnSe Stranski-Krastanow growth of a quantum dot layer in a semiconductor heterostructure, the technique proposed here does not rely on strain and thus results in additional degrees of freedom for choosing composition, concentration, shape, and size of the nanocrystals. Transmission electron microscopy and X-ray diffractometry show that the ZnSe cap layer is of high crystalline quality and provides all parameters for a consecutive growth of Bragg structures, waveguides, or diode structures for electrical injection.

Luminescent properties of Er and Si co-implanted silicates

Abstract An extensive research for optical active materials at 1540 nm is currently being carried out, on the steam of the strong need for optoelectronic devices which can be integrated with the mainstream Si technology. The formation of silica films doped with Er and Si clusters has been shown as one of the promising approaches. We explored the emission properties of different silicate glasses co-implanted with silicon and Er ions to various doses. As starting materials we used soda-lime and aluminium silicates, glasses which show a larger optical bandwidth than silica at 1540 nm. A Si multi-implantation scheme has been adopted for a planar profile. The best conditions to precipitate Si and activate the Er atoms have been investigated. Optimal annealing temperatures have been found around 500 °C, depending on the particular composition of the original glass substrate. The structural analysis of the resulting structures ensures that the best emission properties are the ones for which a phase separation between the implanted Si and the matrix occurs, even without the formation of crystalline aggregates. A comprehensive study of the emission properties is given as a function of the matrix characteristics, Si and Er content, excitation wavelength and power density. It is shown an increase of the emission enhancement of the Er atoms due to the presence of Si cluster when increasing the excitation power. Modelling of the interaction between the absorbing Si nanoprecipitates and the emitting Er atoms has been carried out, in order to estimate the relevant physical parameters which describe the PL process.

Photochemical Coenzyme Regeneration in an Enzymatically Active Optical Material

The photoinduced electron transfer between immobilized thionine and the dinucleotide enzyme cofactors NADH and NADPH in a SiO2 sol−gel matrix is reported. The electron-transfer quenching of thionine luminescence is used to monitor the rate of NADPH oxidation. Using Stern−Volmer quenching curves, the quenching rates in the silica matrix are 1 to 2 orders of magnitude smaller than those in solution. The rate constants for oxidation of NADPH by thionine were measured to be 9.8(±2.9) × 10-3 s-1 in solution and 8.8(±1.0) × 10-4 s-1 in the gel. Within the silica matrix, the photoinduced oxidation of NADPH is combined with the enzymatic reaction of isocitrate dehydrogenase, which uses the oxidized cofactor, NADP+, as an electron acceptor in the oxidation of isocitrate. The encapsulated isocitrate dehydrogenase is active with a Michaelis−Menten constant, KM, of 3 μM and a kcat of 0.67 μM/s per mgenzyme. Because optical sensors use NADPH fluorescence as an indicator of the presence and relative concentration of enzyme substrate, the successful demonstration of photoinduced regeneration of NADP+ makes possible continuous monitoring by the family of dehydrogenase enzymes.

Low loss Photonic Crystal Cladding Waveguide with Large Photonic Band Gap

ABSTRACTLight propagation in a low index core (e.g. SiO2) is realized by a Photonic Band Gap (PBG) cladding waveguide structure with large dielectric index contrast layers (Si/Si3N4). The waveguide is fabricated with a CMOS compatible process. The measured loss for the asymmetric PBG cladding waveguide is about 0.5dB/cm for both polarizations at a wavelength of 1550nm. Potential applications include optical amplification when the SiO2 core is doped with optical active materials (e.g. Er).

Poly(4‐vinylpyridine) as the host ligand of metal‐containing chromophores for second‐order nonlinear optical active materials

AbstractTwo formulas of grafted polymers with metal‐containing chromophores, potentially suitable for second‐order nonlinear optics applications, are described. Two chromophores were obtained from a tridentate ligand coordinated to Cu(II) or Pd(II) ions. The organometallic chromophore fragments were grafted to poly(4‐vinylpyridine) by the pyridinic nitrogen of the host polymer. Some qualities displayed by the new metallated polymers are remarkable: (1) a high value of the first hyperpolarizability coefficient of the chromophores, (2) a high content of the grafted chromophore in the polymers (up to 60 wt %), (3) a considerable increase in the glass‐transition temperatures (up to 240 °C), (4) good thermal stability in air (ca. 280 °C), and (5) good optical transparency of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2987–2993, 2002

Photoluminescence in erbium-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films

Erbium-doped Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT) thin films were grown on (10 1̄2) sapphire substrate with a purpose of developing an active optical material combining both the large electro-optic (EO) effect and lasing or amplification functions. Strong characteristic Er3+ intra-4f shell emission around 1.54 μm is observed at room temperature and a compositional quenching occurred at where the Er content is larger than 0.5 mol %. The introduction of Er in PMN–PT decreased the EO effect, but the EO coefficient still maintain a reasonable value, which is about 0.4×10−16 (m/V)2 at Er content of 0.5 mol %. These results indicate that Er3+-doped PMN–PT can be a potential candidate for integrated optic active devices.

Selective Growth of Polymorphs: An Investigation of the Organic Nonlinear Optical Crystal 5-Nitro-2-thiophenecarboxaldehyde-4-methylphenylhydrazone

An organic nonlinear optical crystal, 5-nitro-2-thiophenecarboxaldehyde-4-methylphenylhydrazone (NTMPH), has been prepared and investigated with regard to polymorphism, growth, and characterization of the structural and physical properties. Recrystallization of NTMPH in various solvents under different conditions showed the existence of three crystalline phases, red greenish plates (NTMPH−I) in space group P21/n, red orange prisms (NTMPH−II) in space group Pna21, and black needle (NTMPH−III) in space group P21/n. The crystal structures of NTMPH showed that three different intermolecular forces dominate the stabilization of one- or two-dimensional structures (called secondary structures in this work) of the three phases of the NTMPH crystals, namely the hydrogen bonding, dipole−dipole interactions, and the van der Waals forces for NTMPH−I, −II, and −III crystals, respectively. The thermal analysis showed that within the trimorphs the NTMPH−I crystal has the lowest thermodynamic stability with the lowest melting point and enthalpy, but NTMPH−II and −III crystals possess a higher thermodynamic stability and are called thermodynamic phases. The NTMPH−I crystal is easily crystallized in most conditions and is called a kinetic phase, whereas NTMPH−II and −III are crystallized with a higher supercooling (equal to a higher chemical potential), which also means that higher energy barriers for the nucleation of NTMPH−II and −III must be overcome. Since crystal structures cannot be designed precisely based on the molecular properties, especially for flexible molecules, the finding and selective growth of interesting polymorphic crystals is an essential step for the development of highly active nonlinear optical materials.