Broad Visible Band Research Articles

Cu-implanted ZnO nanorods array film: An aqueous synthetic approach

Pure and Cu doped ZnO nanorods array are synthesized via two step chemical bath deposition method. The seed layer is prepared by successive ionic layer adsorption reaction (SILAR) method. The synthesized materials have been systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. SEM pictures show the existence of vertically well aligned hexagonal ZnO nanorods. EDAX spectrum confirms the presence of Cu in ZnO nanorods. High intense peak of (002) plane and E2high mode for XRD and Raman spectrum respectively, suggest the ZnO nanorods are adopted c-axis orientation perpendicular to substrate. XRD and Raman analysis shows the presence of tensile strain in Cu doped ZnO nanorods. Effect of Cu doping on lattice constants, unit cell volume and Zn–O bond length of ZnO nanorods have also been studied. Room temperature PL measurement exhibits two luminescence bands in the spectra i.e. UV emission centered at 3.215eV and a broad visible band. Theoretical investigation for capping action of triethanolamine is done by Hartree–Fock(HF) method with 3-21G basis set using Gaussian 09 program package.

Effect of Cr-doping on dielectric, electric and magnetic properties of Zn0.96Cu0.04O nanopowders

Cr doped Zn0.96Cu0.04O nanopowders with different Cr concentrations from 0% to 4% were successfully synthesized by a simple co-precipitation method. X-ray diffraction patterns revealed that all the samples had hexagonal crystal structure and co-doping could not alter its hexagonal structure. The dielectric dispersion and dielectric loss were increased with Cr concentrations due to the increase of charge carrier density, dipoles and vacancies within the grains. At higher frequency, the dielectric loss was found to be low because of the inhibition of domain wall motion. The low dielectric constant and dielectric loss at high frequency region makes it to be a suitable material for high frequency applications. The conductivity was increased by Cr-doping due to the enhanced transition of charge carriers between the grains. The strong suppression of ultraviolet emission at higher Cr revealed the promotion of non-radiative recombination. A broad defect-related visible luminescence band gave evidence for an increase in optically active deep level defects with increased Cr doping level. The combined effect of intrinsic defects and exchange interactions involving Cr ions substituted for Zn in the Zn-Cu-O lattice were responsible for the observed room temperature ferromagnetism. The saturation magnetization of the Cu doped ZnO was decreased by Cr co-doping, which occurred due to the antiferromagnetic coupling of neighboring Cu-Cu ions and Cr-Cr ions. The segregation of spinel ZnCr2O4 phase is responsible for the enhanced coercivity at higher Cr concentration (4%).

Effect of 3d-transition metal doping on the shielding behavior of barium borate glasses: A spectroscopic study

UV–visible and FT infrared spectra were measured for prepared samples before and after gamma irradiation. Base undoped barium borate glass of the basic composition (BaO 40%–B2O3 60mol.%) reveals strong charge transfer UV absorption bands which are related to unavoidable trace iron impurities (Fe3+) within the chemical raw materials. 3d transition metal (TM)-doped glasses exhibit extra characteristic absorption bands due to each TM in its specific valence or coordinate state. The optical spectra show that TM ions favor generally the presence in the high valence or tetrahedral coordination state in barium borate host glass.Infrared absorption bands of all prepared glasses reveal the appearance of both triangular BO3 units and tetrahedral BO4 units within their characteristic vibrational modes and the TM-ions cause minor effects because of the low doping level introduced (0.2%).Gamma irradiation of the undoped barium borate glass increases the intensity of the UV absorption together with the generation of an induced broad visible band at about 580nm. These changes are correlated with suggested photochemical reactions of trace iron impurities together with the generation of positive hole center (BHC or OHC) within the visible region through generated electrons and positive holes during the irradiation process.

Optical and FTIR structural studies of CoO-doped sodium borate, sodium silicate and sodium phosphate glasses and effects of gamma irradiation-a comparative study

Undoped and CoO-doped three binary glass systems, namely sodium borate, sodium silicate and sodium phosphate glasses were prepared by the melt annealing technique. Combined optical and FTIR spectral studies were carried out for the prepared samples before and after being subjected to a gamma dose of 8Mrad (8×104Gy). Optical spectra of the undoped samples before irradiation reveal strong UV absorption varying in depth with the type of glass and such strong UV spectra are related to the presence of unavoidable trace iron impurities within the raw materials used for the preparation of these three basic glasses. CoO-doped (0.25%) glasses show additional visible absorption spectra which are related to the existence of cobalt in the divalent state (Co)2+ ions which are present in two coordination states, namely the octahedral and tetrahedral forms. The broad visible band of Co2+ ions shows in some instances obvious splitting to three component peaks.Gamma irradiation on undoped glasses causes obvious induced UV–visible bands and their extension depends on the type of glass system. Irradiation of CoO-doped glasses causes an obvious increase of absorption within the visible region.Infrared absorption spectra of the undoped three basic glasses reveal IR vibrational bands which are characteristics to the three specific characteristic structural building units within the borate, silicate and phosphate glasses. The introduction of CoO with the doping level causes minor variations of the IR spectra because of the low doping content together with the presence of cobalt ions in structural modifying sites. Gamma irradiation is observed to cause limited changes within the intensities of some bands in the IR spectra which are attributed to changes in bond lengths and/or bond angles of the structural building units by the irradiation process.

Synthesis and spectroscopic and structural studies of ruthenium carbonyl derivatives of N-salicylidene-2-hydroxyaniline Schiff base

The mononuclear ruthenium tricarbonyl derivative mer-[Ru(CO)3(sha)], 1, was synthesized from the reaction of [Ru3(CO)12] with N-salicylidene-2-hydroxyaniline (shaH2) Schiff base. The corresponding reactions of the ruthenium cluster with shaH2 in the presence of a secondary ligand L, L=2-aminobenzimidazole, thiourea, pyridine, and triphenylphosphine, resulted in formation of the dicarbonyl derivatives [Ru(CO)2(sha)(L)], 2–5. The two carbonyl groups in these complexes were attached to the metal in a cis arrangement. In case of bipyridine (bpy) as a secondary ligand the [Ru(CO)2(shaH)(bpy)], 6, where the two CO moieties in a trans position. All the complexes were characterized by elemental analysis, mass, infrared and 1H nuclear magnetic resonance spectra. The ultraviolet–vis spectra of the complexes showed broad visible bands due to metal-to-ligand charge transfer. The stereochemistry and theoretical optimization of the three-dimensional geometry of the ligand and the complexes were determined.

Gamma-rays interactions on optical, FTIR absorption and ESR spectra of 3d transition metals-doped sodium silicophosphate glasses

Glasses of the basic composition mol% 50%P2O5·30%SiO2·20%Na2O together with samples containing one of 3d transition metal oxides (TiO2→CuO) were prepared. Combined optical and FTIR absorption spectra of the prepared glasses were measured before and after gamma irradiation with a dose of 8Mrad (8×104Gy). Undoped sodium phosphosilicate glass reveals strong UV absorption with a peak at 225nm but with no visible bands. Such UV absorption is related to the presence of unavoidable trace iron impurities contaminated with the chemicals used for preparation of this glass. 3d-transition metal ions-doped glasses exhibit characteristic absorption bands extended in the UV/Vis regions which are characteristics for the specific TM ions. Gamma irradiation causes broadness of the UV absorption bands in the spectrum of the undoped glass and the resolution of three peaks at about 250, 310 and 340nm beside the appearance of an induced broad visible band centered at about 450nm. Glasses doped with 3d TM ions reveal variations in their response towards gamma irradiation. FTIR absorption spectra show extended broad vibrational bands which are related to the presence of both vibrational modes due to silicate and phosphate groups but the later groups are predominant due to the high percent of P2O5 (50%). The presence of TM ions within the dopant level (0.2%) causes no obvious changes in the number and position of the IR structural vibrational bands. ESR spectra of 3d TM-ions-doped glasses reveal quite distinct spin resonance after gamma irradiation indicating that unpaired electrons increase through the capturing or releasing of energetic electrons during the irradiation process.

A Highly Symmetric Metal–Organic Framework Based on a Propeller-Like Ru-Organic Metalloligand for Photocatalysis and Explosives Detection

Ru(H2dcbpy)32+, one of the Ru(bpy)32+ (dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid, bpy = 2,2′-bipyridine) derivatves, has been used as a propeller-like photoactive metalloligand to coordinate with indium(III) ions to form a highly symmetric metal–organic framework [InRu(dcbpy)3][(CH3)2NH2]·6H2O (1), and the cubic microcrystals of 1 have been acquired through modified procedures. Compound 1 manifests broad visible light absorption band and strong red light emission with long decay lifetime, both of which are originated from the metal-to-ligand charge transfer of the Ru(dcbpy)34– metalloligands. Because of the highly light-harvesting and strong redox nature of the Ru(dcbpy)32+ units in 1, its photocatalysis activities were determined by visible light-induced photodegradation of methyl orange experiments. The results indicate that 1 can be a stable and good visible-light driving heterogeneous photocatalyst. Meanwhile, the sensing properties of 1 were also evaluated, and the result shows that 1 can select...

Gamma rays interaction with copper doped lithium phosphate glasses

Undoped and copper-doped lithium phosphate glasses were prepared. CuO-doped glasses possess characteristic greenish color which deepens with the increase of CuO content. Experimental optical absorption spectra of the undoped lithium phosphate glasses reveal strong ultraviolet absorption bands and no visible bands are observed. These strong UV bands are assumed to originate from unavoidable trace iron ions contamination within the chemicals used for the preparation of the glass. The optical absorption spectra of the CuO-doped phosphate glasses reveal the same UV absorption as observed in the undoped samples beside an extra broad visible absorption band which splits to some component peaks. Such visible spectra are related to the presence of divalent copper (Cu2+) ions in distorted octahedral coordination. Gamma irradiation of the undoped sample produces induced defects generated through the liberation of pairs of electrons and positive holes. CuO-doped glasses show some shielding behavior towards successive gamma irradiation especially at high CuO contents. FTIR absorption spectra of the studied glasses indicate the appearance of characteristic vibrational bands due to phosphate groups. Gamma irradiation causes minor effects on the FTIR spectra, but the bands due to water molecules are strongly affected by gamma irradiation because of loose bonding within the glass network.

Highly π-extended polymers based on phenanthro-pyrazine: Synthesis, characterization, theoretical calculation and photovoltaic properties

Two novel narrow bandgap conjugated polymers containing phenanthro-pyrazine unit have been successfully synthesized by the Stille coupling reaction. Comparing to the common polymers containing dithiophen-quinoxaline or dithiophen-thieno[3,4-b]pyrazine moiety, the conjugation degree of these new polymers is extended through the direction perpendicular to the main chain by introducing phenanthrene-9,10-dione to maintain a rigid conjugated bridge. The obtained polymers exhibit solution-processing ability, high thermal stabilities, broad visible absorption bands and narrow optical bandgaps. Theoretical studies disclose that the P2 exhibits wholly coplanar conformation in 1-D and 2-D direction, and the PCE value is 6-folded higher than P1 under the same photovoltaic measurement condition.

Spectral properties and shielding behavior of gamma irradiated MoO3-doped silicophosphate glasses

Combined optical and infrared absorption spectra of prepared molybdenum ions in sodium silicophosphate host glasses were investigated before and after gamma irradiation with a dose of 8Mrad (8×104Gy). The undoped base sodium silicophosphate glass reveals strong charge transfer ultraviolet absorption but with no visible bands. This strong UV absorption is related to the presence of contaminated trace iron impurities (mainly Fe3+ ions) within the raw materials used for the preparation of this host glass. The MoO3 doped glasses exhibit extra characteristic absorption bands due to the presence of molybdenum ions in three possible valence states, the trivalent, pentavalent and hexavalent forms. Gamma irradiation of the base undoped glass increases the extension of optical absorption within the UV spectrum and produces an extra broad visible band centered at 520nm. Such radiation-induced spectra are interpreted by assuming the formation of new induced color centers through the absorption of released electrons and formed positive holes during the irradiation process. Also, the possible formation of induced centers through photochemical transformation of some Fe2+ ions to Fe3+ ions by accepting positive holes. The presence of molybdenum ions is assumed to compete with the suggested irradiation reactions by capturing electrons and positive holes during the irradiation process.Infrared absorption spectra of the undoped and MoO3-doped glasses reveal broad IR vibrational bands which are attributed to the presence of combined characteristic vibrational IR modes due to main phosphate and partner silicate groups. The addition of MoO3 (0.5–1.5%) as dopant level causes no changes in the number and position of the main characteristic absorption bands. Gamma irradiation did not cause any marked changes in the IR spectra and the maintainance of the same main IR bands due to the stability of the network containing dual compact two glass-formers units and the presence of molybdenum ions as shielding component. The changes in intensities of some bands are correlated with changes in bond angles and/or bond lengths of some structural units as previously suggested by several authors. E.S.R. data of the MoO3-doped glasses reveal indication of several valence states of molybdenum ions as suggested by optical measurements. The irradiated samples show the change in resonance spectra of high MoO3-doped glasses which can be related to change of some Mo6+ to Mo5+ ions as deduced from optical spectra.

Effect of co-substitution of nitrogen and fluorine in BaTiO3 on ferroelectricity and other properties

BaTiO3, with both nitrogen and fluorine substituted for oxygen, has been prepared and the properties of the doped material with the composition BaTiO2.8N0.1F0.1 have been studied. The color of the sample changes to light green on doping, accompanying a broad visible absorption band with its edge at 2.5 eV. The first-order ferroelectric transition changes to a broad transition on doping along with a decrease in the dielectric constant. We have examined the local structure, electronic structure and polar lattice dynamical properties of N and F co-substituted BaTiO3 using first-principles density functional theory-based calculations and derived the mechanism of the diffuse ferroelectric transition observed here with a broad peak in the temperature-dependent dielectric response. The calculated Born charges clearly reveal a strong disparity in the interaction of N, O and F with Ti: N being the most ferro-active, with a highly anomalous charge, and F being the least active, with an almost nominal charge. This originates from an electronic structure in which the top-most valence band is constituted of the 2p states of N, while the electronic states of F lie deep in the energy band, resulting in a local structure with short covalent Ti–N and long ionic Ti–F bonds. Disorder in these hetero ferro-active anions leads to a relaxor-like diffuse phase transition and a reduction in polarization. Calculations confirm the reduction of 0.65 eV in the bandgap of BaTiO3, which changes from indirect to direct type.

Defect formation of gamma irradiated MoO3-doped borophosphate glasses

Borophosphate glasses of the basic composition (50P2O5, 30B2O3, 20Na2Omol%) containing different doping molybdenum oxide percents (0.16–0.98) were prepared by melting and annealing method. Infrared and UV–visible absorption spectroscopic measurements before and after gamma irradiation were carried out. The base undoped borophosphate glass reveals strong UV absorption bands but with no visible bands and these UV bands are related to unavoidable trace iron impurities contaminated within the raw materials used for the preparation of this glass. The introduction of MoO3 (in doping ratio) into this glass produces an additional UV band and a broad visible band and their intensities increase with the MoO3 content. These additional bands are related to both Mo6+ and Mo5+ ions. The base undoped borophosphate glass shows retardation effect towards gamma irradiation. Gamma irradiation produces marked changes in the UV–visible spectra of MoO3-doped glasses. Such changes can be related to the production of induced defects from photochemical reactions and the generation of positive holes. Infrared absorption spectrum of the undoped borophosphate glass reveals complex vibrational bands due to the presence of both phosphate groups beside borate groups with triangular and tetrahedrally coordinated units. The introduction of MoO3 causes some limited variations in the FTIR spectra. Gamma irradiation produces minor changes in the intensities of some IR bands. Such changes are related to the changes in the bond angles and/or bond lengths of few structural groups upon irradiation while the main structural groups remain unchanged in their number and position.

Excitation intensity- and temperature-dependent photoluminescence in layered structured Tl2GaInSe2S2 crystals

Photoluminescence spectra of Tl2GaInSe2S2 layered crystals have been registered in the temperature range of 17–62 K and in the wavelength region of 525–690 nm. A broad visible photoluminescence band centered at 590 nm (2.10 eV) was observed at T = 17 K. Variation of emission band has been studied as a function of laser excitation intensity in the 0.1–55.7 mW cm−2 range. The analysis of the spectra reveals that the peak energy position changes with excitation intensity (blue shift). The radiative transitions from moderately deep donor level to shallow acceptor level were suggested to be responsible for the observed band. From X-ray powder diffraction study, the parameters of monoclinic unit cell of Tl2GaInSe2S2 were determined.

Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts

A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340-400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420-520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO2 composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO2 is 3 and 10 times higher than that of N:GQD/TiO2 and P25 TiO2 under visible light irradiation, respectively.

Synthesis, Isolation, Structure Elucidation, and Color Properties of 10-Acetyl-pyranoanthocyanins

Grape anthocyanins reacted with diacetyl, a secondary metabolite of microorganisms involved in winemaking, to form 10-acetyl-pyranoanthocyanins, a type of anthocyanin-derived pigment similar to other vitisin-type pyranoanthocyanins found in red wines. The structures of 10-acetyl-pyranomalvidin-3-β-O-glucoside and 10-acetyl-pyranopeonidin-3-β-O-glucoside were confirmed by spectroscopic methods (UV-vis, MS/MS, and NMR) after their synthesis and isolation. In contrast to other vitisin-type pyranoanthocyanins, the newly described 10-acetyl-pyranoanthocyanins exhibited differentiated color-related properties. They showed an important tendency to occur as colorless hemiacetals at C-10 under wine pH conditions, while co-occurrence of flavylium cation and quinoidal base yielded a broad visible absorbance band around 510-520 nm. Moreover, they easily reacted with bisulfite in acidic aqueous solution (pH 2.0), but the expected bleaching was not observed. Bisulfite bonded to the carbonyl of 10-acetyl substituent instead of the expected C-10 position of the pyranoanthocyanin core, thus giving rise to a red pigment hypsochromically shifted toward orangish nuances (maximum absorbances at 487-491 nm).

Facile synthesis of Zn1−xCuxO nanorods with a very broad visible band

Zn1−xCuxO nanorods with different Cu concentrations are prepared by a hydrothermal method. Bent and aggregated nanorods are obtained, which is attributed to centripetal surface tension of the evaporation and coagulation processes of the water film on the ZnO nanorods. The broad visible band consists of one violet, three blue, and one green emission. The violet emission is due to the transition of electrons from zinc interstitial (Zni) levels to the valance band. The three blue emissions may be attributed to the transition from extended Zni levels, which are slightly below the simple Zni level, to the valance band. The change of the green emission may be the result of competition between oxygen vacancies (VO) and zinc vacancies (VZn).

Spectroscopic properties of gamma irradiated TiO2 doped lithium phosphate glasses

Optical absorption spectra of undoped and TiO2-doped lithium phosphate glasses were measured before and after successive gamma irradiation. Undoped lithium phosphate glasses show strong UV absorption, while TiO2-doped samples exhibit surplus two broad visible bands due to the presence of Ti3+ ions in predominant ratio. Gamma irradiation produces UV and visible induced bands but the presence of TiO2 seems to cause some shielding effects towards successive gamma irradiation. Infrared absorption spectral measurements indicate the presence of characteristic phosphate groups and the effect of gamma irradiation is limited to small changes in the intensities of some absorption bands. The experimental results are interpreted on the bases of current views on the structure of the studied host glass in relation to properties studied.

Synthesis, strong room-temperature PL and photocatalytic activity of ZnO/ZnWO4 rod-like nanoparticles

Abstract Zinc oxide (ZnO)/zinc tungstate (ZnWO4) rod-like nanoparticles with diameters in the range of 6–11 nm and length of about 30 nm were synthesized by a low temperature soft solution method at 95 °C in the presence of non-ionic copolymer surfactant. It was found that their crystallinity was enhanced with the increase of heating time from 1 h up to 120 h. The photoluminescence (PL) measurements showed very strong, narrow UV band peaked at 3.30 eV and a broad visible band peaking at 2.71 eV with a shoulder at about 2.53 eV, for λexc

Optical and FTIR studies of CuO-doped lead borate glasses and effect of gamma irradiation

CuO doped lead borate glasses of the composition PbO 70%–B2O3 30% with varying CuO contents were prepared. UV–visible and infrared spectroscopic studies were measured before and after successive gamma irradiation with two different doses namely 2 and 8Mrad. The experimental results indicate that the undoped sample reveals strong UV–near visible absorption while copper doped samples show additional broad visible band due to (Cu2+) ions.FT infrared absorption spectrum reveals vibrational bands due to triangular and tetrahedral borate groups together with the sharing of Pb–O vibrations.CuO-doped glasses have been found to show a shielding behavior towards the effects of progressive gamma irradiation causing the maintenance of the spectral curves. The changes in the UV–visible and infrared spectral data are discussed in relation to the states of copper ions and structural evolution caused by the change in glass composition including the CuO.

Synthesis Sol-Gel Derived Highly Transparent ZnO Thin Films for Optoelectronic Applications

In this work, ZnO thin films were derived by sol-gel using two different techniques; dip coating and spin coating technique. The films were deposited onto glass substrate at room temperature using sol-gel composed from zinc acetate dehydrate, monoethanolamine, isopropanole, and de-ionized water, the films were preheated at 225?C for 15 min. The crystallographic structures of ZnO films were investigated using X-ray diffraction (XRD); the result shows that the good film was prepared at dip coating technique, it was polycrystalline and highly c-orientation along (002) plane, the lattice constant ratio (c/a) was calculated at (002), it was about 1.56. The structure of thin films, prepared by spin coating technique, was amorphous with low intensity and wide peaks. The optical properties of the prepared film were studied using UV-VIS spectrophotometer with the range 190 - 850 nm, and by using the fluorescence spectrometer. The optical characterization of ZnO thin films that were prepared by the dip coating method have good transmittance of about 92% in the visible region, it can be noted from the fluorescence spectrometer two broad visible emission bands centered at 380nm and 430 nm. The optical energy gaps for the direct and indirect allowed transitions were calculated, the values were equal 3.2 eV and 3.1 eV respectively. Dip coating technique create ZnO films with potential for application as transparent electrodes in optoelectronic devices such as solar cell.