Investigation of properties of the sonomodified ZnO-CeO2 system

Abstract

The ultrasonic treatment (UST) influence on properties of the ZnO-CeO₂ system (atomic ratios Zn/Ce?=?25:75, 50:50, and 75:25) is studied. A decrease of the size of particles of the oxides, the formation of Zn-Ce-O nanocompositions, and an increase in the specific surface area of the samples are established. It is shown that the sonochemical treatment of oxide zinc-cerium mixtures allows one to increase their photocatalytic activity in the safranin T degradation process. A blue shift of the edge absorption in powder-like samples and an increase in the band gap energy (Eg) are fixed by the UV-vis spectroscopy. The catalytic test of the sonochemically treated ZnO-CeO₂?=?50:50 catalyst in the reaction of ethanol selective oxidation shows a possibility of its use in two processes: i) production of acetaldehyde with high selectivity in a low-temperature reaction (235?°C) with the recycle of the raw material, ethanol, and ii) hydrogen production without CO formation at temperatures more than 300?°C.     

Modification of amorphous hydrogenated silicon by co-sputtered aluminum

The electronic and optical properties of a-Si_1?xH_x have been modified by the incorporation of aluminum. Samples were prepared by rf sputtering in a hydrogenated atmosphere from a composite silicon-aluminum target. This paper reports on several modified material parameters including the optical band gap, electrical conductivity, and thermal activation energy. Aluminum concentrations up to 10.6% in the target have been investigated. It is observed that the optical band gap remains constant at 1.83 eV for Al concentrations up to 2.7%. For higher concentrations there is a marked decrease in optical gap. The conductivity initially decreases with small Al concentration and the activation energy increases, characteristic of compensation of the inherently n-type material. For higher Al concentrations the conductivity increases by seven orders of magnitude and the activation energy decreases to a minimum of about 0.2 eV. The increase in conductivity can be explained by both the movement of the Fermi level and the shrinking band gap. Microprobe analyses have also been performed to determine the amount of Al actually incorporated into the films. Finally, implications of these results are discussed and compared to previously reported results on gas phase doping and ion implantation.     

Investigation on the blue photorefractive properties varied with MgO codoping in Ru:Fe:LiNbO3 crystals

Mg:Ru:Fe:LiNbO₃ crystals with various doping concentration of MgO have been grown by Czochralski method. The type of charge carriers and photorefractive properties in Mg:Ru:Fe:LiNbO₃ crystals were measured by two‐wave coupling method using Kr⁺ laser (476 nm) and He‐Ne laser (633 nm) as light sources. We found that holes were the dominant charge carriers under blue light irradiation while electrons were the dominant charge carriers under red light irradiation. Mg²⁺ ions behaved no longer as damage resistant, but promoter to the photorefractive properties at 476 nm wavelength. The photorefractive properties under blue light improved with the increase concentration of Mg²⁺ ions. The enhancement mechanisms of the blue photorefractive were suggested. Experimental results definitely showed that Mg‐doped two‐centre Ru:Fe:LiNbO₃ was a promising blue photorefraction material for holographic volume storage.     

Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF₃ substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for 1a, 446 nm for 1b, 385 nm for 2a, and 399 nm for 2b, respectively, in good agreement with the energy gap (ΔE_L-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the S₀→S₁ transition. 2b has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.

[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]     

Synthetically tuned structural variations in coordination polymers based on dicyanamide toward diverse physical properties

Three new two-dimensional coordination polymers (CPs), {Ni[N(CN)₂]₂(H₂O)₂·2DMAC}_n for 1, {Ni[N(CN)₂]₂(DMAC)₂}_n for 2, and {Co[N(CN)₂]₂(DMSO)₂}_n for 3, have been synthesized with different synthetic methods. The crystallographic analysis indicates that CPs 1 and 3 crystallize in the monoclinic system with space group of P2₁/c, while CP 2 crystallizes in the orthorhombic system with space group of Pnma. CPs 1 and 3 exhibit the antiferromagnetic properties, while CP 2 shows the weak ferromagnetic property. The solid-state luminescence properties of CPs 1–3 have also been investigated. Compared with the dicyanamide, 1 and 2 show the blue shift with emission maximum around 310?nm, while CP 3 shows the band at 335?nm.     

Origin of blue and green colouration in sulphur containing alkali borate glasses

Simple binary sodium and potassium borate glasses containing sulphur were prepared. Depending on the composition of the glass and the quantity of sulphur added the glasses produced were blue, green or yellow. The absorption spectra of these glasses were measured in the range of 300–700 nm.The blue colour is characterized by an absorption band at 585 nm which is attributed to S₃^?.The green colour is characterized by two absorption bands; the band at 585 nm observed in the spectra of the blue glasses and a more intense band at 390 nm. The latter is attributed to S₂^? and the green colouration to the presence of both S₂^? and S₃^? where the S₂^? state predominates.     

Organic Superconductors: A Survey of Low Dimensional Phenomena

An experimental investigation of the electronic properties of the conducting cation radical salts (TMTSF)₂X, has shown how the development of superconductivity at low temperature is affected by the low dimensional character of the band structure. Electron Schottky tunnel spectroscopy has given evidence that the critical temperature is not an intrinsic property of the intrachain superconducting pairing. The pairing energy in (TMTSF)₂PF₆ (P=11 Kbar) derived from the pseudo-gap in the quasi particle density of states amounts to ≈40 K i.e about 40 times the critical temperature. Consequently, properties such as conductivity, thermal conductivity, thermopower, etc… of these Quasi-One-Dimensional Superconductors are to a large extent dominated by the onset of 1-D fluctuating superconducting pairing below 30 K or so. Moreover, the stabilization of these fluctuations into a 3-D ordered superconducting state at higher temperature, namely 12 K for (TMTSF)₂PF₆, (P=11 Kbar) seems feasible via chemically induced chain bridging. The large pairing energy as well as the presence of a spin density waves state in the (T.P) phase diagram of these organic superconductors suggest the importance of the Coulomb interactions in the mechanism of Cooper pair formation.     

Optical Transitions of Agi and Agbr Clusters in Zeolite Fau

Abstract

AgI and AgBr clusters are both incorporated into the cages of zeolite FAU. The absorption spectra of these clusters, whose loading densities varied from dilute to four AgI and AgBr molecules per supercage, are discussed. In both samples, the lowest absorption band shifts to the lower energy side with increasing loading density. The large blue shift in AgI clusters compared to the bulk can be qualitatively explained by the model of strong quantum confinement of the photoexcited electron-hole pair. In the sample of AgBr clusters with four molecules per cage, however, the energy of the lowest absorption band is close to that of the lowest direct transition of AgBr in bulk. This apparently weak quantum confinement in the photo-excited state seems to originate from the singular band structure in the bulk, i.e., AgBr is the indirect gap material.     

Modeling of energy bands in ultra-thin layer quantum nanostructures for solar cell applications

In this paper we propose a simple calculation of the energy band in nano-structured meta-materials based on ultra-thin periodic Si/SiO₂ layers (quantum-well superlattice) for third-generation solar cell application. For this purpose, the Schrödinger equation (with periodic Bloch's conditions) is numerically solved considering the exact potential profiles of both the valence and conduction bands of the Si/SiO₂ system. This method allows us to analyze the carrier energy band structure and to extract the essential electronic properties (bandgaps, miniband widths) of such 1-D periodic nanostructures. The energy band structure and more particularly the meta-material bandgap is found to strongly depend on quantum well thickness and spacing.     

Theoretical study on the electronic structures and spectral properties of two series of osmium(II) complexes with different substituent groups

Two series of osmium(II) complexes with different substituent groups (-CF₃, -N(CH₃)₂) have been studied by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, to investigate their electronic structures, absorption, and emission properties. The influence of different substituted groups on their photophysical properties has also been explored. The lowest energy absorption and emission wavelengths calculated are in good agreement with the available experimental values. Besides, ionization potential (IP), electron affinities (EA), and reorganization energy (λ) were calculated to evaluate the charge transfer and balance properties between hole and electron. It is expected that the theoretical studies could provide valuable information for the phosphorescent osmium(II) material for use in the organic light-emitting diodes.     

Expanded Prussian Blue Analogue Based on Octahedral {Nb<Subscript>6</Subscript>} Clusters and {K<Subscript>2</Subscript>} Dimers as Nodes

Abstract  The preparation, structures, and characterization of two new compounds containing octahedral niobium cyanochloride clusters as building units and (Et₄N)⁺ as cation are reported. The reaction between Nb₆Cl₁₄ · 8H₂O, KCN and (Et₄N)Cl led to the formation of (Et₄N)₄[Nb₆Cl₁₂(CN)₆] · 2.67H₂O (1) which crystallizes in triclinic P-1 space group (No. 2) with a = 12.552(2), b = 12.818(2), c = 12.919(2) ?, α = 105.157(3)°, β = 104.188(3)°, γ = 117.390(2)°, V = 1611.7(5) ?³ and Z = 1. 1 has a 2D hydrogen-bonded layer structure based on [Nb₆Cl₁₂(CN)₆]⁴⁻ units connected through hydrogen bonding between cyanide ligands and solvent water molecules. In the presence of large excess of K⁺ ions, similar reaction leads to formation of K₂(Et₄N)₂[Nb₆Cl₁₂(CN)₆] (2) which crystallizes in the tetragonal I4/m space group (No. 87) with a = b = 10.9597(3), c = 19.178(1) ?, V = 2303.6(2) ?³ and Z = 2. Its 3D structure is based on [Nb₆Cl₁₂]²⁺ and [K₂]²⁺ nodes bridged by cyanide ligands to form an expanded Prussian blue type framework with (Et₄N)⁺ acting as charge compensating ions. Index Abstract  An expanded Prussian blue type 3D framework based on hexanuclear {Nb₆} and dinuclear {K₂} units which are bridged by cyanide linker was synthesized and characterized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and light-emitting properties of a carbazole-containing hyperbranched conjugated poly(phenylene vinylene)

Abstract

A new carbazole-containing hyperbranched conjugated poly(phenylene vinylene) (Hyper-PCPPV) was synthesized through the Wittig polycondensation polymerization. Hyper-PCPPV has good solubility in common organic solvents and showed excellent thermal stability up to 425?°C with less than 5% weight loss. The photophysical properties of Hyper-PCPPV were investigated and compared with a carbazole-containing linear conjugated poly(para-phenylene vinylene) (Linear-PCPPV). An absorption maximum of Hyper-PCPPV film was determined at 353?nm which was far blue shifted than that of Linear-PCPPV (403?nm). Hyper-PCPPV showed blue photoluminescence (PL) peak at 448?nm. In addition, Hyper-PCPPV exhibited almost no excimer or aggregate emission peaks even when the polymer film was annealed at 80?°C for 30?min in air condition.     

Linear optical properties of BaNaB9O15, BaLiB9O15 and SrLiB9O15 glasses

Transparent BaNaB₉O₁₅ (BNBO), BaLiB₉O₁₅ (BLBO) and SrLiB₉O₁₅ (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and Differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The optical properties for these as-quenched glasses were investigated. The refractive index, optical band gap, Urbach energy and Fermi energy were determined. The average electronic polarizability calculated from the refractive index expression.     

Characterization of the reversible photoinduced optical changes in Sb-based glasses

Changes occurring in absorption coefficients when glasses in the SbPO₄–WO₃ binary system were irradiated by light, at the edge of the absorption band, were measured in real time. These glasses present good thermal and optical properties and photoinduced changes in the absorption coefficients are reversible by heat treatment around 150 °C. Subsequent recording/erasing cycles could be made without sample degradation. The sensitivity of the induced optical changes was studied for different wavelengths, light powers and energy of light dose exposures, and for different compositions of the glasses. The changes in the absorption coefficients of the glass samples were accompanied by a color change from yellow to blue, and were also characterized by visible spectroscopy. The color changes occurred through the entire volume of the glass (∼2 mm thickness) for the Ar-ion laser lines at the edge of the absorption band.     

Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi₂O₃-P₂O₅ glass with low-P₂O₅ content (20-25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF₂. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF₂ substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s-6p interband transition in Bi³⁺ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.     

Correlation Between the Fiber Texture of Nickel Electrodeposits as Supports and the Reflected Light Band from Cholesteric Liquid Crystals

In previous works [Mol. Cryst. Liq. Cryst., 61, 31(1980); 95, 323 (1983)] the influence of the solid support sorptive properties on the color (reflected light band) of cholesteric liquid crystals was revealed. Qualitative and quantitative (visible diffuse reflectance spectroscopy) measurements at several temperatures on bare metal (Zn, Fe, Cu, Al) surfaces mechanically treated, on chemically and electrolytically prepared ZnO and Fe₃O₄, on electrolytically prepared γ₁,-and γ₂-Al₂O₃, on copper surfaces electroplated with copper and on electrolytically prepared γ₂-Al₂O₃ under several current densities, covered with a cholesteric mixture were carried out and correlated with the sorptive properties of the support. In the present work similar optical measurements at several temperatures with the same mixture of cholesterics as the one of the previous works on nickel electrodeposits with different fiber texture were carried out, compared each other and correlated with the deduced sorptive abilities of the deposits.     

Synthesis and characterization of Cu2ZnSnSe4 nanocrystals prepared by one pot route

Quaternary compound Cu₂ZnSnSe₄ (CZTSe) is one of the most promising absorber layer materials for thin film solar cells. In present work, the CZTSe nanocrystals were successfully synthesized via one pot route, and the influences of reaction temperature on the structural, compositional, morphological and optical properties of as‐synthesized CZTSe nanocrystals were investigated in detail via X‐ray powder diffraction (XRD), energy dispersive X‐ray spectrometry (EDS), transmission electron microscopy (TEM) and UV‐Vis spectrophotometry, respectively. The characterization results of as‐synthesized nanocrystals, under optimal synthesis condition (250 °C, 1 h), indicated that the nanocrystals was monodispersed with polycrystalline, the size was in the range of 10–15 nm, and the band gap energy was around 1.44 eV which is very closed to the best band gap energy for the solar cell. All results suggested that the as‐synthesized CZTSe nanocrystals were good light absorber layer material for thin film solar cell.     

Growth and optical homogeneity investigations of Fe and Fe:Mn codoped LiNbO3 crystals

Lithium niobate (LiNbO₃) crystals doped with Fe and Fe:Mn were grown by Czochralski technique. The doping concentrations of Fe and Mn were optimized. Transmission studies reveal broad absorption band centered at 488 nm. The UV cutoff observed for Fe doped LiNbO₃ is 358 nm whereas for Fe:Mn codoped LiNbO₃ is 352 nm. This decrease in UV cutoff for Fe and Mn codoped LiNbO₃ compared to only Fe doped LiNbO₃ is due to the increase in Li/Nb ratio. Optical homogeneity was assessed using conoscopy and birefringence interferometry. Dark and photo conductivity measurements prove that LiNbO₃ is a negative photo conducting material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and optical properties of chalcogenide amorphous semiconductors modified with Ni

The electrical and optical properties of the chalcogenide semiconductor (Se₃₂Te₃₂As₄Ge₃₂)_100?xNixitx have been studied. As the Ni concentration is increased the electrical dc conductivity is drastically increased and variable range hopping conduction becomes dominant even above room temperature. The optical energy gap decreases with the Ni concentration from 1.18–0.95 eV. Ni-atoms in the chalcogenide semiconductor donate free electrons which occupy the gap state. This occupation causes the shift of the Fermi level toward the conduction band. It is an effect of this shift that the thermal activation energy is decreased. The decrease in optical energy gap is independent of the shift of the Fermi level and is ascribable to the appearance of the additional level located at 0.95 eV above the top of the valence band. This level originates from the 3d-level of the Ni-atom.     

Synthesis,characterization and crystal structure of a mononuclear iron(III) complex derived from 4-bromo-2-[(pyridin-2-ylmethylimino)methyl]phenol

A nitrate salt of bis[4-bromo-2-(pyridin-2-ylmethyliminomethyl)phenolato]iron(III), [Fe(C₁₃H₁₀BrN₂O)₂].NO₃, has been obtained and characterized by elemental analysis and X-ray single crystal determination. The complex crystallizes in the tetragonal space group P4₂/n with unit cell dimensions a = b = 17.608(3) ?, c = 17.199(3) ?, V = 5332.4(15) ?³, Z = 8, R ₁ = 0.0444 and wR2 = 0.0902. The complex consists of a [Fe(C₁₃H₁₀BrN₂O)₂]⁺ cation and a nitrate anion. The Fe atom in the cation is six-coordinated in an octahedral geometry. In the crystal structure, molecules are linked through weak C–H⋯O intermolecular hydrogen bonds, forming chains running along the c axis. Supplementary material CCDC-607149 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at http://www.ccdccam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.