Showing papers on "Absorption band published in 2011"

A Thin Film Broadband Absorber Based on Multi-sized Nanoantennas

Abstract: We experimentally demonstrate an infrared broadband absorber for TM polarized light based on an array of nanostrip antennas of several different sizes. The broadband property is due to the collective effect of magnetic responses excited by these nano-antennas at distinct wavelengths. By manipulating the differences of the nanostrip widths, the measured spectra clearly validate our design for the purpose of broadening the absorption band. The present broadband absorber works very well in a wide angular range.

A thin film broadband absorber based on multi-sized nanoantennas

Abstract: We experimentally demonstrate an infrared broadband absorber based on an array of nanostrip antennas of several different sizes. The broadband property is due to the collective effect of magnetic responses excited by these nanoantennas at distinct wavelengths. By manipulating the differences of the nanostrip widths, the measured spectra clearly validate our design for the purpose of broadening the absorption band.

Absorption Spectra and Excited State Energy Levels of the N719 Dye on TiO2 in Dye-Sensitized Solar Cell Models

Abstract: We have investigated the absorption spectrum and the alignment of ground and excited state energies for the prototypical N719 Ru(II) sensitizer adsorbed on an extended TiO2 model by means of high level DFT/TDDFT calculations. The calculated and experimental absorption spectra for the dye on TiO2 are in excellent agreement over the explored energy range, with an absorption maximum deviation below 0.1 eV, allowing us to assign the underlying electronic transitions. We find the lowest optically active excited state to lie ca. 0.3 eV above the lowest TiO2 state. This state has a sizable contribution from the dye π* orbitals, strongly mixed with unoccupied TiO2 states. A similarly strong coupling is calculated for the higher-lying transitions constituting the visible absorption band centered at ca. 530 nm in the combined system. An ultrafast, almost instantaneous, electron injection component can be predicted on the basis of the strong coupling and of the matching of the visible absorption spectrum and density...

Optical and Structural Properties of ZnO Thin Films Fabricated by Sol-Gel Method

Abstract: Highly oriented and transparent ZnO thin films have been fabricated on ultrasonically cleaned quartz substrates by the sol-gel technique. X-ray diffraction, UV-VIS, FTIR, photoluminescence and SEM are used to characterize ZnO thin films. X-ray diffraction study show that all the films prepared in this work have hexagonal wurtzite structure, with lattice constants a = b = 3.260 A, c = 5.214 A. The optical band gap energy of the thin films is found to be direct allowed transition ~3.24 eV. The FTIR spectrum of the film has the characteristics ZnO absorption band at 482 cm −1 . The photoluminescence spectrum of the samples has an UV emission peak centred at 383 nm with broad band visible emission centred in the range of 500 - 600 nm.

Near-infrared spectra of clinopyroxenes: Effects of calcium content and crystal structure

Abstract: Pyroxenes are among the most common minerals in the solar system and are ideally suited for remote geochemical analysis because of the sensitivity of their distinctive spectra to mineral composition. Fe 2+ is responsible for the dominant pyroxene absorptions in the visible and near-infrared, but substitutions of other cations such as Ca 2+ change the crystal structure and site geometries and thus the crystal field splitting energies of the Fe cations. To define spectral systematics resulting from major pyroxene cations (Ca 2+ ,M g 2+ , and Fe 2+ ), we focus on a suite of pyroxenes synthesized with only Ca 2+ ,M g 2+ , and Fe 2+ in the two octahedral sites, specifically examining the effect of Ca 2+ on pyroxene absorption bands. The modified Gaussian model is used to deconvolve pyroxene spectra into component bands that can then be linked directly to crystal field absorptions. In orthopyroxenes and low-Ca clinopyroxenes, Ca 2+ -content has a strong and predictable effect on the positions of the absorption bands. At a threshold of Wo30, the crystal field environment stagnates and the M2 bands cease to change significantly as more Ca 2+ is added. At Wo50, when most of the M2 sites are filled by Ca 2+ , band positions do not change drastically, although the presence and strengths of the 1 and 2 lm bands are affected by even trace amounts of Fe 2+ in the M2 site. It is thus apparent that next-nearest neighbors and the distortions they impose on the pyroxene lattice affect the electronic states around the Fe 2+ cations and control absorption band properties.

Photoconductivity measurements of the electronic structure of organic solar cells

Abstract: Experimental and theoretical studies of the electronic structure of bulk heterojunction (BHJ) organic solar cells are reported. The photoconductivity spectral response of the solar cells has a weak absorption band extending from the band-gap energy down to 1 eV due to charge-transfer optical excitation at the interface between the polymer and the fullerene. The low-energy absorption indicates an exponential band tail of localized states and an absorption model based on the one-electron joint density of electronic states accounts for the data. Transient photoconductivity measurements of the carrier mobility exhibit a temperature-dependent carrier dispersion. Data analysis for the particular case of transport in the BHJ structure is developed. A multiple trapping model of the dispersive transport is consistent with localized band tail states having a comparable density-of-states distribution to those observed by optical absorption. Theoretical calculations of the density of states including disorder in the \ensuremath{\pi}-\ensuremath{\pi} spacing of the polymer chains also shows exponential band tailing. A density-of-states model is developed from the data and is discussed.

Visible-light photocurrent response of TiO2–polyheptazine hybrids: evidence for interfacial charge-transfer absorption

Abstract: We investigated photoelectrodes based on TiO2–polyheptazine hybrid materials. Since both TiO2 and polyheptazine are extremely chemically stable, these materials are highly promising candidates for fabrication of photoanodes for water photooxidation. The properties of the hybrids were experimentally determined by a careful analysis of optical absorption spectra, luminescence properties and photoelectrochemical measurements, and corroborated by quantum chemical calculations. We provide for the first time clear experimental evidence for the formation of an interfacial charge-transfer complex between polyheptazine (donor) and TiO2 (acceptor), which is responsible for a significant red shift of absorption and photocurrent response of the hybrid as compared to both of the single components. The direct optical charge transfer from the HOMO of polyheptazine to the conduction band edge of TiO2 gives rise to an absorption band centered at 2.3 eV (540 nm). The estimated potential of photogenerated holes (+1.7 V vs.NHE, pH 7) allows for photooxidation of water (+0.82 V vs.NHE, pH 7) as evidenced by visible light-driven (λ > 420 nm) evolution of dioxygen on hybrid electrodes modified with IrO2 nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO2–polyheptazine interface is a complex and flexible system energetically favorable for proton-transfer processes required for water oxidation. Apart from water splitting, this type of hybrid materials may also find further applications in a broader research area of solar energy conversion and photo-responsive devices.

Cerium (III) doping effects on optical and thermal properties of PVA films

Abstract: Cerium chloride (CeCl 3 ) doped polyvinyl alcohol (PVA) films were prepared by casting technique. The effect of CeCl 3 concentrations on the structural, optical and thermal properties of the PVA films was studied by X-ray diffraction (XRD), FT-IR, UV-visible, transmittance ( T ), reflectance ( R ), differential scanning calorimetry (DSC) and thermogravimetry (TG). Both of the XRD and the DSC results affirm the increase in amorphousity. Absorption spectra of the doped films have shown an absorption band at 260 nm assigned to the trivalent state of cerium ions. Absorption, transmittance and reflectance spectra were used for the determination of the optical constants. The results indicate that the optical band gap ( E g ) was derived from Tauc's extrapolation and decreases with the cerium content. The refractive index increases with monotonic behavior as the cerium content increases. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomernico model for obtaining the dispersion parameters. The obtained optical parameters were found to be strongly affected by CeCl 3 dopant. Thermal analysis showed that the thermal parameters of PVA are enhanced by CeCl 3 . The dependence of the activation energy of the decomposition temperature on doping level was estimated.

Phonon-mediated magnetic polaritons in the infrared region

Abstract: Magnetic polaritons that couple electromagnetic waves with magnetic excitation can be used for tailoring the radiative properties of materials in energy-harvesting and other applications. Previous studies used metallic microstructures to induce magnetic responses. With rigorous coupled-wave analysis (RCWA), transmission enhancement with a SiC slit array and coherent thermal emission with a SiC deep grating is theoretically demonstrated in the infrared within the phonon absorption band. The field distributions and the agreement in the resonance frequencies predicted from both RCWA and LC circuit models strongly suggest that magnetic polaritons exist in the SiC microstructures. This type of magnetic polariton is mediated by vibration of atoms in polar materials (i.e., optical phonons), rather than by free electrons in metals. Our results suggest that phonon-mediated magnetic polaritons have promising applications such as filters and selective coherent emitters in the infrared spectral region.

Optical and electrical properties of SnS semiconductor crystals grown by physical vapor deposition technique

Abstract: Tin sulfide (SnS) is a material of interest for use as an absorber in low cost solar cells. Single crystals of SnS were grown by the physical vapor deposition technique. The grown crystals were characterized to evaluate the composition, structure, morphology, electrical and optical properties using appropriate techniques. The composition analysis indicated that the crystals were nearly stoichiometric with Sn-to-S atomic percent ratio of 1.02. Study of their morphology revealed the layered type growth mechanism with low surface roughness. The grown crystals had orthorhombic structure with (0 4 0) orientation. They exhibited an indirect optical band gap of 1.06 eV and direct band gap of 1.21 eV with high absorption coefficient (up to 10(3) cm(-1)) above the fundamental absorption edge. The grown crystals were of p-type with an electrical resistivity of 120 Omega cm and carrier concentration 1.52 x 10(15) cm(-3). Analysis of optical absorption and diffuse reflectance spectra showed the presence of a wide absorption band in the wavelength range 300-1200 nm, which closely matches with a significant part of solar radiation spectrum. The obtained results were discussed to assess the suitability of the SnS crystal for the fabrication of optoelectronic devices. (C) 2011 Elsevier B.V. All rights reserved.

Ion irradiation of carbonaceous interstellar analogues - Effects of cosmic rays on the 3.4 μm interstellar absorption band

Abstract: Context. A 3.4 μm absorption band (around 2900 cm-1), assigned to aliphatic C-H stretching modes of hydrogenated amorphous carbons (a-C:H), is widely observed in the diffuse interstellar medium, but disappears or is modified in dense clouds. This spectral difference between different phases of the interstellar medium reflects the processing of dust in different environments. Cosmic ray bombardment is one of the interstellar processes that make carbonaceous dust evolve. Aims. We investigate the effects of cosmic rays on the interstellar 3.4 μm absorption band carriers. Methods. Samples of carbonaceous interstellar analogues (a-C:H and soot) were irradiated at room temperature by swift ions with energy in the MeV range (from 0.2 to 160 MeV). The dehydrogenation and chemical bonding modifications that occurred during irradiation were studied with IR spectroscopy. Results. For all samples and all ions/energies used, we observed a decrease of the aliphatic C-H absorption bands intensity with the ion fluence. This evolution agrees with a model that describes the hydrogen loss as caused by the molecular recombination of two free H atoms created by the breaking of C-H bonds by the impinging ions. The corresponding destruction cross section and asymptotic hydrogen content are obtained for each experiment and their behaviour over a large range of ion stopping powers are inferred. Using elemental abundances and energy distributions of galactic cosmic rays, we investigated the implications of these results in different astrophysical environments. The results are compared to the processing by UV photons and H atoms in different regions of the interstellar medium. Conclusions. The destruction of aliphatic C-H bonds by cosmic rays occurs in characteristic times of a few 108 years, and it appears that even at longer time scales, cosmic rays alone cannot explain the observed disappearance of this spectral signature in dense regions. In diffuse interstellar medium, the formation by atomic hydrogen prevails over the destruction by UV photons (destruction by cosmic rays is negligible in these regions). Only the cosmic rays can penetrate into dense clouds and process the corresponding dust. However, they are not efficient enough to completely dehydrogenate the 3.4 μm carriers during the cloud lifetime. This interstellar component should be destroyed in interfaces between diffuse and dense interstellar regions where photons still penetrate but hydrogen is in molecular form.

Infrared Spectrum of the Hydrated Proton in Water

Abstract: Reactive molecular dynamics simulations have been utilized to calculate the infrared (IR) spectra of acidic HCl solutions of varying concentration with the goal of achieving a better understanding of the spectral features of the hydrated excess protons in bulk water. To incorporate the essential physics of the hydrated proton, we carried out the simulations using the specialized self-consistent iterative multistate empirical valence bond (SCI-MS-EVB) method, which is a form of multiconfigurational (reactive) molecular dynamics. After the pure water absorption background was removed, the calculated difference spectra are in good agreement with prior experimental results. The continuous broad absorption band in the acidic IR spectrum is, for the first time, interpreted based on the concept of a dynamically distorted Eigen cation, H9O4(+), which has been shown to provide the most accurate description for the charge defect character of the hydrated excess proton in liquid water.

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR, optical and IR techniques

Abstract: Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B 2 O 3 (R = Mg, Ca and Sr) and 10SrO + (30 − x )ZnO + 60B 2 O 3 + x CuO ( x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu 2+ ions. The values of spin-Hamiltonian parameters indicate that the Cu 2+ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration ( N ) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu 2+ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility ( χ ) was calculated at different temperatures and the Curie constant was evaluated from the 1/ χ - T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies ( E g ) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.

Line-broadening effects in the powder infrared spectrum of apatite

Abstract: The crystallinity of natural and synthetic apatite samples is often determined from the broadening of ν4 PO4 infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study, the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated. The temperature dependence of the infrared spectrum (10–270 K) is used to assess the respective contributions of homogeneous broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties of apatite based on first-principles density functional theory calculations. The linewidth of the weak ν1 PO4 absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison, the other more intense PO4 bands are more sensitive to long-range electrostatic effects.

Optical and other spectroscopic studies of lead, zinc bismuth borate glasses doped with CuO

Abstract: 10MO·20Bi 2 O 3 ·(70− x )B 2 O 3 · x CuO [M=Pb, Zn] with x =0, 0.4 and 0.8 (wt%) glasses were synthesized by the melt-quenching technique and were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Physical parameters, like density, and spectroscopic studies (optical absorption, EPR, FTIR and photoluminescence) were used to understand the role of modifier oxide and CuO in the glass matrix. A red shift of the absorption band corresponds to 2 B 1g → 2 B 2g transition of Cu 2+ ions from P2 to Z4 samples and the increase of hyperfine splitting factor ( A ‖ ) from P2 to Z2 shows that with the integration of PbO by ZnO the electron density around copper ion is increased. It is also supported by the gradual increase in theoretical optical basicity values of ZnO mixed glasses, as compared to that of PbO mixed glass matrix. Reduced bismuth radicals are found in undoped and 0.4% CuO doped glasses of both the series. Analysis of the absorption and emission studies indicates that the concentration of luminescence centers of bismuth ions (Bi 3+ ions in UV region) is decreased by the integration of ZnO as well as by increasing the dopant concentration. In lead series PbO 4 and BiO 3 units are increased from P2 to P4 and in zinc series BiO 3 units are decreased from Z0 to Z4. The conductivity of the glass matrices is increased in both the series with the dopant of CuO.

Analysis of poly(amidoamine) dendrimer structure by UV-vis spectroscopy.

Abstract: We report a UV–vis spectroscopic study of four different types of poly(amidoamine) dendrimers The results indicate that the degree of protonation of the interior tertiary amines of these dendrimers correlates directly to an absorption band with λmax in the range of 280–285 nm Specifically, at low pH, the tertiary amines are protonated and the 280–285 nm band is absent However, at elevated pH, when these groups are deprotonated, this band appears Similar results were obtained for a simple model compound The dependence of the 280–285 nm band on the chemical state of the tertiary amines of the dendrimers was confirmed by complexing them with Pd2+ and Pt2+ In this case the band disappears, and it only reappears when the metal ions are decomplexed following reduction with BH4– Finally, filtration experiments showed that the absorption band between 280−285 nm arises exclusively from intact, or nearly intact, dendrimers rather than low-molecular-weight fragments

PH-controlled construction of Cu(I) coordination polymers: in situ transformation of ligand, network topologies, and luminescence and UV-vis-NIR absorption properties.

Abstract: Two new complexes [CuI3(L1)I3]n (1, L1 = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole) and [CuI3(L2)I2]n (2, L2 = 2,5-bis(4-pyridyl)-1,2,4-triazolate) are controllably formed by using aqueous ammonia to regulate the pH value of the reaction involving CuI and L1. Interestingly, L2 of 2 is in situ generated from the ring transform of L1 when increase the pH value of the reaction. 1 exhibits 2-D layer, while 2 shows 3-D MOFs with a novel 3-nodal 4,4,5-connected net topology of an unprecedented Point (Schlafli) symbol: (4·52·62·7)(54·82)(43·5·66). Although both 1 and 2 are built of CuI and similar ligands, different arrangements of CuI chains and ligands endow them with different physical properties. 1 displays a strong pure red luminescence emission, while 2 is nonluminescent and shows a broad absorption band covering the whole UV–vis-NIR spectrum range. The emissive excited states of 1 and the charge transitions of the optical absorption for 2 are solved by DFT calculations.

The 9.7 and 18 μm silicate absorption profiles towards diffuse and molecular cloud lines-of-sight

Abstract: Context. Studying the composition of dust in the interstellar medium (ISM) is crucial for understanding the cycle of dust in our galaxy. Aims. The mid-infrared spectral signature of amorphous silicates, the most abundant dust species in the ISM, is studied in different lines-of-sight through the Galactic plane, thus probing different conditions in the ISM. Methods. We have analysed ten spectra from the Spitzer archive, of which six lines-of-sight probe diffuse interstellar medium material and four probe molecular cloud material. The 9.7 μm silicate absorption features in seven of these spectra were studied in terms of their shape and strength. In addition, the shape of the 18 μm silicate absorption features in four of the diffuse sightline spectra were analysed. Results. The 9.7 μm silicate absorption bands in the diffuse sightlines show a strikingly similar band shape. This is also the case for all but one of the 18 μm silicate absorption bands observed in diffuse lines-of-sight. The 9.7 μm bands in the four molecular sightlines show small variations in shape. These modest variations in the band shape are inconsistent with the interpretation of the large variations in τ9.7/E(J − K) between diffuse and molecular sightlines in terms of silicate grain growth. Instead, we suggest that the large changes in τ9.7/E(J − K) must be due to changes in E(J − K).

Structural, Optical, and Electronic Properties of a Series of 3,4-Propylenedioxythiophene Oligomers in Neutral and Various Oxidation States

Abstract: A series of 3,4-propylenedioxythiophene (ProDOT) oligomers (nPHex) with dihexyl side chains and methylthio end-capping units was synthesized as a model of poly(3,4-alkylenedioxythiophene)s. The slope of the linear relationship between the energy of the absorption maxima of nPHex in the neutral states and the reciprocal of the number of monomer units (1/n) was found to be comparable to that of 3,4-ethylenedioxythiophene (EDOT) oligomers, suggesting that both the ProDOT and the EDOT oligomers have a similar effective conjugation. In cyclic voltammetry measurements, both the first and second oxidation waves and the third and fourth waves were shown to merge into one peak with increasing chain length. The stepwise chemical oxidations of nPHex with SbCl5 in CH2Cl2 at room temperature gave their stable cationic species in various oxidation states, and it was found that only the radical cations (polarons) have an obvious absorption band in the visible region. Interestingly, when the absorption spectra of tetrame...

Relationship between Molecular Aggregation Structures and Optical Properties of Polyimide Films Analyzed by Synchrotron Wide-Angle X-ray Diffraction, Infrared Absorption, and UV/Visible Absorption Spectroscopy at Very High Pressure

Abstract: The relationship between the molecular aggregation structures and the optical properties of fully aromatic and semialiphatic polyimide (PI) films were analyzed by synchrotron wide-angle X-ray diffraction (WAXD), infrared absorption, and UV/visible absorption spectroscopy at very high pressures up to 8 GPa. The PIs showed significant reduction in the interchain distances in the first stage of compression up to 1 GPa, which resulted in an appreciable decrease in the interchain free volume. In addition, reduction in the C−C bond lengths of aromatic rings by ca. 0.7% was confirmed by the pressure-induced high wavenumber shift of the infrared stretching vibration of the PIs. Furthermore, pressure-induced bathochromic shifts were observed in the locally excited (LE) absorption band of PIs, which are related to the enhanced van der Waals interaction caused by the reduced interchain distances. The intensity of the charge transfer (CT) absorption band of s-BPDA/PDA poly(p-phenylene biphenyltetracarboximide) PI was...

Structures and vibrational spectroscopy of partially reduced gas-phase cerium oxide clusters

Abstract: This work demonstrates that the most stable structures of even small gas-phase aggregates of cerium oxide with 2–5 cerium atoms show structural motifs reminiscent of the bulk ceria. This is different from main group and transition metal oxide clusters, which often display structural features that are distinctly different from the bulk structure. The structures of Ce2O2+, Ce3O4+, and (CeO2)mCeO+ clusters (m = 0–4) are unambiguously determined by a combination of global structure optimizations at the density functional theory level and infrared vibrational predissociation spectroscopy of the cluster–rare gas atom complexes. The structures of Ce2O2+ and Ce2O3+ exhibit a Ce–O–Ce–O four-membered ring with characteristic absorptions between 430 and 680 cm−1. Larger clusters have common structural features containing fused Ce–O–Ce–O four-membered rings which lead to intense absorption bands at around 500 and 650 cm−1. Clusters containing a terminal CeO bond show a characteristic absorption band between 800 and 840 cm−1. For some cluster sizes multiple isomers are observed. Their individual infrared signatures are identified by tuning their relative population through the choice of He, Ne or Ar messenger atoms. The present results allow us to benchmark different density functionals which yield different degrees of localization of unpaired electrons in Ce 4f states.

Facile structure and property tuning through alteration of ring structures in conformationally locked phenyltetraene nonlinear optical chromophores

Abstract: A series of phenyltetraene-based nonlinear optical (NLO) chromophores 1a–c with the same donor and acceptor groups, but different tetraene bridges that are partly connected by various sizes of aliphatic rings, have been synthesized and systematically investigated. The interposed conjugated tetraene segments in three chromophores studied are based on isophorone, (1S)-(−)-verbenone, and 3,4,4-trimethyl-2-cyclopentenone, respectively. This kind of structural alteration has significant effect on the intrinsic electronic structures and physical properties of these highly polarizable chromophores as revealed by a variety of characterization techniques. The introduction of the verbenone- and trimethylcyclopentenone-based tetraene bridges could significantly improve the glass-forming ability of chromophores 1b and 1c in comparison with the highly crystalline characteristics of isophorone-based chromophores 1a. More importantly, chromophores 1a–c exhibited distinct optical features in absorption band shape, solvatochromic behavior, as well as energy band gap from the UV-vis-NIR absorption measurements. Quantum mechanical calculations using density functional theory (DFT) were also used to evaluate second-order NLO properties of these chromophores. The electro-optic (EO) coefficients of 1a–c in poled polymers with the 10 wt% chromophore content showed an apparent decrease from 78 pm V−1 for 1a to 42 pm V−1 for 1c. This decrease is attributed to the gradual decrease of the molecular hyperpolarizability (β) of the chromophores which is associated with the progressive cyanine-like electronic structure from the isophorone-based 1a to the cyclopentenone-based 1cchromophore.

Synthesis, structural and optical characterization of Ni-doped ZnO nanoparticles

Abstract: Nanocrystalline Zn1−xNixO (x = 0.00, 0.02, 0.04, 0.06, 0.08) powders were synthesized by a simple sol–gel autocombustion method using metal nitrates of zinc, nickel and glycine. Structural and optical properties of the Ni-doped ZnO samples annealed at 800 °C are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis using X-rays (EDAX), UV–visible spectroscopy and photoluminescence (PL). X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a hexagonal wurtzite structure and secondary phase (NiO) was observed with the sensitivity of XRD measurement with the increasing nickel concentration (x ≥ 0.04). The lattice constants of Ni-doped ZnO nanoparticles increase slightly when Ni2+ is doped into ZnO lattice. The optical absorption band edge of the nickel doped samples was observed above 387 nm (3.20 eV) along with well-defined absorbance peaks at around 439 (2.82 eV), 615(2.01 eV) and 655 nm (1.89 eV). PL measurements of Ni-doped samples illustrated the strong UV emission band at ~3.02 eV, weak blue emission bands at 2.82 and 2.75 eV, and a strong green emission band at 2.26 eV. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.