Absorption Bands In Spectra Research Articles

Spectroscopy of red dravite from northern Tanzania

Low-Fe dravite with a formula of Na0.66Ca0.16Mg2.62Fe0.33Mn0.02Ti0.02Al5.95B3Si6.04O27(OH)4 is described from Engusero Sambu, northern Tanzania (On maps, Engusero Sambu may be found to be marked as belonging to Kenya, but in reality, it is located near the border in northern Tanzania). The sample has an unusual red color that is distinctly different from the red dravite from the Osarara, Narok district, in Kenya that was formerly studied by Mattson and Rossman (Phys Chem Miner 14:225–234, 1984) and Taran and Rossman (Am Mineral 87:1148–1153, 2002). This unique sample has been characterized by optical and Mossbauer spectral measurements to investigate underlying cause of the intense bands in absorption spectra that give rise to the red color. These features are shown to be caused by exchange-coupled Fe3+–Fe3+ interactions. Thermal annealing of the samples causes an increase in Fe3+ contents due to oxidation of [Y]Fe2+. However, heat treatment does not change the high-energy absorption edge, which is probably caused by intense ligand-to-Fe3+ charge-transfer UV bands. In fact, Mossbauer results show that high-temperature annealing initiates breakdown of the tourmaline into an Fe oxide and causes accompanying redistribution of Fe3+ within the structure. Because of the popularity of tourmaline as a gemstone, this work has implications for understanding the causes of color in tourmaline, facilitating recognition of the distinctions between naturally occurring and treated tourmalines in the gem industry and enabling heat treatments for color enhancement.

Magnetic Field-Induced Splitting of Optical Spectra in Silicon Nanotubes: Tight Binding Calculations

The splitting of band structure and absorption spectra, for silicon nanotubes (SiNTs) under axial magnetic field, are studied using the tight binding approximation. It is found that band splitting is approximately proportional to the magnitude of magnetic field as \(\frac {\Delta E}{E_{g}}=\nu _{ii} \frac {\Phi }{{\Phi }_{0}}\) where ν i i is the splitting rate. For Si g-NTs, we calculated the splitting rate of the two first bands nearest to the Fermi level in the Γ point and found that it can be fitted with a two degree polynomial as \(\nu _{ii}={\sum }_{j=0}^{2}{a^{i}_{j}}x^{j}\) where \(x=\frac {1}{n^{2}}\) and for sufficiently large diameter Si g-NTs, the ν i i can be fitted by a linear function. For semiconductor Si h-NTs the ν 11 = 6 but ν 22 and ν 33 show radial dependence. Also we found that applying magnetic field leads to splitting for all peaks in the low energy ranges for all zigzag Si h-NTs and Si g-NTs. The first peak of group (I) of Si g-NTs does not show any splitting in the magnetic field and for all metallic Si h-NTs, the magnetic field leads to creating a peak in the energy range less than 0.2 eV where this peak arises from energy gap created around Fermi energy.

Inhibitory effects of deferasirox on the structure and function of bovine liver catalase: a spectroscopic and theoretical study

Deferasirox (DFX), as an oral chelator, is used for treatment of transfusional iron overload. In this study, we have investigated the effects of DFX as an iron chelator, on the function and structure of bovine liver catalase (BLC) by different spectroscopic methods of UV–visible, fluorescence, and circular dichroism (CD) at two temperatures of 25 and 37 °C. In vitro kinetic studies showed that DFX can inhibit the enzymatic activity in a competitive manner. KI value was calculated 39 nM according to the Lineweaver–Burk plot indicating a high rate of inhibition of the enzyme. Intrinsic fluorescence data showed that increasing the drug concentrations leads to a significant decrease in the intrinsic emission of the enzyme indicating a significant change in the three-dimensional environment around the chromophores of the enzyme structure. By analyzing the fluorescence quenching data, it was found that the BLC has two binding sites for DFX and the values of binding constant at 25 and 37 °C were calculated 1.7 × 107 and 3 × 107 M−1, respectively. The static type of quenching mechanism is involved in the quenching of intrinsic emission of enzyme. The thermodynamic data suggest that hydrophobic interactions play a major role in the binding reaction. UV–vis spectroscopy results represented the changes in tryptophan (Trp) absorption and Soret band spectra, which indicated changes in Trp and heme group position caused by the drug binding. Also, CD data represented that high concentrations of DFX lead to a significant decreasing in the content of β-sheet and random coil accompanied an increasing in α-helical content of the protein. The molecular docking results indicate that docking may be an appropriate method for prediction and confirmation of experimental results and also useful for determining the binding mechanism of proteins and drugs. According to above results, it can be concluded that the DFX can chelate the Fe(III) on the enzyme active site leading to changes in the function and structure of catalase which can be considered as a side effect of this drug and consequently has an important role in hepatic complications and fibrosis.

Effect of In–2N heavy co-doping and preferred orientation on the optical band gap and absorption spectrum of ZnO

Nowadays although the In–N co-doping effects on the optical band gap and absorption spectrum of ZnO are studied extensively, all of the In–N co-doped ZnO materials are of random doping, and the preferred orientation doping using the unpolarized structure of ZnO has not been considered so far. Therefore, in this paper, based on the density functional theory using first principles plane-wave ultrasoft pseudopotential (GGA+U) method, the densities of states and absorption spectra of un-doped and the In–N heavily co-doped Zn1-xInxO1-yNy (x= 0.0625-0.03125, y=0.0625-0.125) in different orientations are calculated. The results show that in the same doping mode, the larger the volume of doping system, the higher the total energy and the formation energy are and the narrower the optical band gap is; the red shifting of absorption spectrum becomes more significant with the increase of In–2N co-doping amount. Those are in good agreement with the experimental results. Under the condition of different doping manners and the same In–2N co-doped concentration, the co-coped In–N atoms along the c-axis orientation, have the narrower optical band gap and more significant red shifting of absorption spectrum than the In–N atoms with the orientation perpendicular to the c-axis. We believe that these results may be helpful for designing and preparing the new photocatalyst materials of In–N heavily co-doped ZnO.

Advanced Flexible CIGS Solar Cells Enhanced by Broadband Nanostructured Antireflection Coatings

ABSTRACTFlexible copper indium gallium diselenide (CIGS) solar cells on lightweight substrates can deliver high specific powers. Flexible lightweight CIGS solar cells are also primary candidates for building-integrated panels. In all applications, CIGS cells can greatly benefit from the application of broadband and wide-angle AR coating technology. The AR coatings can significantly improve the transmittance of light over the entire CIGS absorption band spectrum. Increased short-circuit current has been observed after integrating AR coated films onto baseline solar panels. NREL’s System Advisor Model (SAM) has predicted up to 14% higher annual power output on AR integrated vertical or building-integrated panels. The combination of lightweight flexible substrates and advanced device designs employing nanostructured optical coatings together have the potential to achieve flexible CIGS modules with enhanced efficiencies and specific power.

Study of the effect of Cu heavy doping on band gap and absorption spectrum of ZnO

Contradictory experimental absorption spectra blue shift and red shift results have been reported in the literatures. To solve this problem, this study investigates the electronic structure and absorption spectra of Zn1−xCuxO (x=0, 0.0313 and 0.0625, respectively) and Zn32CuO32 supercells employing first-principles calculations with GGA+U method. By increasing the Cu substitutional doping concentration from 3.13% to 6.25%, the following results are obtained: increased magnetic properties, narrower band gaps, and a significant red shift in the absorption spectrum. These findings are in good agreement with the experimental results. The changes of band gap and absorption spectrum for interstitial doping and substitutional doping are opposite.

Ag-PMMA structures for application in infra-red optical range

In proposed work the preparation of ordered microstructures of silver with arc shape on the patterned polymer surfaces is described. The most attractive feature of these structures is the ability to manipulate with their optical properties. Structures were fabricated by laser scanning of poly(methyl methacrylate) doped by porphyrine. Simple lattice and the fishnet structure were obtained on the polymer surface. Both structures were coated using silver shadow evaporation method. Prepared structures were analysed by AFM, SEM and FIB-SEM methods. Then electrical and optical properties were estimated by resistance measurements and infrared spectroscopy. In this work preparation of sinusoidal pattern and fishnet structure on the polymer surface is described. Artificial nature of the prepared structure manifests itself by strong absorption band in absorption spectra and as an increase of reflectivity in reflection spectra near absorption band.

Band engineering and absorption spectra in compressively strained Ge0.92Sn0.08/Ge (001) double quantum well for infrared photodetection

AbstractWe report a theoretical investigation of strained Ge1−xSnx/Ge (001)‐oriented quantum wells as a bulding block in active region of infrared photodetector. The electronic band parameters, gaps, discontinuities and effective masses for heterointerfaces between compressively strained Ge1−xSnx and relaxed Ge have beencomputed at room temperature. From this preliminary and mendatory work, we conclude that pseudomorphic Ge1−xSnx alloys become direct band gap semiconductors at a Sn‐fraction of 15.3%, e.g. a lattice mismatch as high as 2.3%. Due to achievable critical layer thickness and mainly solid solubility limit, a type‐I compressively strained Ge/Ge0.92Sn0.08/Ge (double) quantum well is studied by solving Schrödinger equation without and applied bias voltage. A strong absorption coefficient (> 1×104 cm−1) and a Stark shift of the direct transition between 2.01 μm and 2.25 μm at large external fields (40kV/cm) are attractive characteristics for the design of infrared photodetectors (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate.

The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarbo-xylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2 and 3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of 6.0 ± 2.5 fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells, which may lead to reduced recombination effects and improved efficiencies of future devices.

Phenolics Impart Au3+-Stress Tolerance to Cowpea by Generating Nanoparticles

While evaluating impact of Au nanoparticles on seed germination and early seedling growth of cowpea, HAuCl4 was used as control. Seedlings of cowpea raised in HAuCl4, even at concentration as high as 1 mM, did not show any suppression in growth. Accordingly, Au3+, despite being a heavy metal, did not alter levels of stress markers (viz. proline and malondialdehyde) in cowpea. Interestingly, cowpea turned clear pale yellow HAuCl4 solutions colloidal purple during the course of seed germination and seedling growth. These purple colloidal suspensions showed Au-nanoparticle specific surface plasmon resonance band in absorption spectra. Transmission electron microscopic and powder X-ray diffraction investigations confirmed presence of crystalline Au-nanoparticles in these purple suspensions. Each germinating seed of cowpea released ∼35 nmoles of GAE of phenolics and since phenolics promote generation of Au-nanoparticles, which are less/non toxic compared to Au3+, it was contemplated that potential of cowpea to withstand Au3+ is linked to phenolics. Of the different components of germinating seed of cowpea tested, seed coat possessed immense power to generate Au-nanoparticles, as it was the key source of phenolics. To establish role of phenolics in generation of Au-nanoparticles (i) seed coat and (ii) the incubation medium in which phenolics were released by germinating seeds, were tested for their efficacy to generate Au-nanoparticles. Interestingly, incubation of either of these components with Au3+ triggered increase in generation of Au-nanoparticles with concomitant decrease in phenolics. Accordingly, with increase in concentration of Au3+, a proportionate increase in generation of Au-nanoparticles and decrease in phenolics was recorded. In summary, our findings clearly established that cowpea possessed potential to withstand Au3+-stress as the phenolics released by seed coat of germinating seeds possess potential to reduce toxic Au3+ to form non/less toxic Au-nanoparticles. Our investigations also pave a novel, simple, green and economically viable protocol for generation of Au-nanoparticles.

First principles study of the effect of high V doping on the optical band gap and absorption spectrum of ZnO

Nowadays, the studies on optical band gap and absorption spectrum of V doped ZnO have presented two distinctly different experimental results, that is, the blue shift increases and decreases when the mole fraction of impurity increases in a range from 0.0417 to 0.0625. To solve this contradiction, according to the first-principles plane-wave ultrasoft pseudopotential of the density functional theory, we set up models for a pure ZnO cell and two supercells of Zn1-xVxO (x=0.0417, 0.0625) to calculate the total density of state, partial density of state, magnetism and absorption spectrum through using the method of GGA+U. The calculation results indicate that with the doping amount increasing from 2.083 at% to 3.125 at%, the magnetic moment of doping system increases and magnetism augments, too. Moreover, the volume of doping system increases, the total energy decreases and the formation energy becomes lower, thereby making the system more stable. Meanwhile, its optical band gap becomes wider, and the absorption spectrum shifts toward low energy. The calculation results are consistent with the experimental data.

First-principle study on the effect of high Pr doping on the optical band gap and absorption spectra of TiO2

Nowadays, the studies on band gap and absorption spectrum of TiO2 doped with Pr lead to opposite conclusions. Two experimental results about red-shift and blue-shift are reported in the literature. We have set up models for pure TiO2 and different doping concentrations of Pr-doped TiO2 to calculate the electronic structure and absorption spectrum based on the first-principle plane-wave ultrasoft pseudopotential in terms of the density functional theory (DFT) to slove the above problem. Results indicate that under the condition of heavy doping Pr, compared with the pure TiO2, as the Pr concentration increases the atomic charge of the doped system reduces and the total energy of the doped system becomes higher, and its formation energy will be greater. This makes the stability decline, the band gap narrowed, the absorption spectrum red-shift, and the absorption strength more significant. The results of the calculation is in agreement with the experimental data.

Spectroscopic studies of the binding of Cu(II) complexes of oxicam NSAIDs to alternating G-C and homopolymeric G-C sequences

Drugs belonging to the Non-steroidal anti-inflammatory (NSAID) group are not only used as anti-inflammatory, analgesic and anti-pyretic agents, but also show anti-cancer effects. Complexing them with a bioactive metal like copper, show an enhancement in their anti-cancer effects compared to the bare drugs, whose exact mechanism of action is not yet fully understood. For the first time, it was shown by our group that Cu(II)-NSAIDs can directly bind to the DNA backbone. The ability of the copper complexes of NSAIDs namely meloxicam and piroxicam to bind to the DNA backbone could be a possible molecular mechanism behind their enhanced anticancer effects. Elucidating base sequence specific interaction of Cu(II)-NSAIDs to the DNA will provide information on their possible binding sites in the genome sequence. In this work, we present how these complexes respond to differences in structure and hydration pattern of GC rich sequences. For this, binding studies of Cu(II) complexes of piroxicam [Cu(II)-(Px)2 (L)2] and meloxicam [Cu(II)-(Mx)2 (L)] with alternating GC (polydG–dC) and homopolymeric GC (polydG–polydC) sequences were carried out using a combination of spectroscopic techniques that include UV–Vis absorption, fluorescence and circular dichroism (CD) spectroscopy. The Cu(II)-NSAIDs show strong binding affinity to both polydG–dC and polydG–polydC. The role reversal of Cu(II)-meloxicam from a strong binder of polydG–dC (Kb=11.5×103M−1) to a weak binder of polydG–polydC (Kb=5.02×103M−1), while Cu(II)-piroxicam changes from a strong binder of polydG–polydC (Kb=8.18×103M−1) to a weak one of polydG–dC (Kb=2.18×103M−1), point to the sensitivity of these complexes to changes in the backbone structures/hydration. Changes in the profiles of UV absorption band and CD difference spectra, upon complex binding to polynucleotides and the results of competitive binding assay using ethidium bromide (EtBr) fluorescence indicate different binding modes in each case.

Self-assemblies of tricationic porphyrin on inorganic polyphosphate

Self-assemblies formed by the new synthesized tricationic porphyrin derivative (TMPyP3+) on the polyanionic inorganic polyphosphate (PPS) in aqueous solution were studied using different spectroscopic techniques and DFT calculation method. From the fluorescence quenching of the bound TMPyP3+ molecules and their Raman spectra we conclude that porphyrin chromophores form the stable π–π stacking-assemblies onto PPS polyanions. The transformation of the Soret band in absorption spectra at different PPS/TMPyP3+concentration ratios evidences that the assemblies are mixtures of J- and H-aggregates. Molecular modeling performed shows that the flexibility of PPS strand allows a realization of spiral or “face-to-face” one-dimensional structures formed by porphyrin molecules arranged in parallel and antiparallel modes. The peculiarity of PPS structure allows a formation of two porphyrin stacks on opposite sides of polymer strands that result in the appearance of higher-order aggregates. Their size was estimated from the light scattering data. Distinctions between TMPyP3+ and TMPyP4 aggregation on PPS template are discussed.

Theoretical Modeling of Deuteration-Induced Shifts of the 0–0 Bands in Absorption Spectra of Selected Aromatic Amines: The Role of the Double-Well Potential

The harmonic approximation fails for inversion of the NH2 group in the ground state of aromatic amines as this vibration is characterized by a symmetric double-well potential with relatively small energy barrier. In such cases, the standard harmonic vibrational analysis is inapplicable: the inversion frequency calculated for the bottom of the potential well is strongly overestimated, while it attains imaginary values for the planar conformation of the molecule. The model calculations are discussed taking explicitly into account the presence of the double-well potential. The study is initially focused on reproduction of the deuteration-induced shifts of the 0-0 absorption band for anthranilic acid. The (incorrect) harmonic frequency of the NH2 inversion is replaced by a better one, obtained from numerical calculations employing a simple, quartic-quadratic model for the double-well potential, which is parametrized using just the harmonic frequency of the inversion and the height of the energy barrier. This operation brings theoretical results to qualitative agreement with experiment. A still better match is achieved with a modified version of the model that accounts for mixing of the NH2 inversion mode with other normal modes while retaining the initial simplicity of one-dimensional approach. The corrected results show surprisingly good accuracy, with deviations of the calculated shifts from the experimental values reduced to less than 5 cm(-1). In order to test the performance of the model for systems with higher energy barrier for the NH2 inversion, we have measured the LIF excitation spectra of three different amminobenzonitriles. Partial assignment of the 0-0 bands has been achieved based on their relative intensities for samples with different isotopic exchange ratios. Calculated shifts are in excellent agreement with experimental values for the identified bands. Theoretical predictions are used to complete the assignment of the 0-0 bands in the spectra of the studied amminobenzonitriles.

A Density Functional Study of Furofuran Polymers as Potential Materials for Polymer Solar Cells

The structural, electronic, and optical properties of poly(3-hexylthiophene) (P3HT) have been comprehensively studied by density functional theory (DFT) to rationalize the experimentally observed properties. Rather, we employed periodic boundary conditions (PBC) method to simulate the polymer block, and calculated effective charge mass from the band structure calculation for describing charge transport properties. The simulated results of P3HT are consistent with the experimental results in band gaps, absorption spectra, and effective charge mass. Based on the same calculated methods as P3HT, a series of polymers have been designed on the basis of the two types of building blocks, furofurans and furofurans substituted with cyano (CN) groups, to investigate suitable polymers toward polymer solar cell (PSC) materials. The calculated results reveal that the polymers substituted with CN groups have good structural stability, low-lying FMO energy levels, wide absorption spectra, and smaller effective masses, which are due to their good rigidity and conjugation in comparison with P3HT. Besides, the insertion of CN groups improves the performance of PSC. Synthetically, the designed polymers PFF1 and PFF2 are the champion candidates toward PSC relative to P3HT.

A study of quantum well solar cell structures with bound-to-continuum transitions for reduced carrier recombination

A bound-to-continuum quantum well solar cell structure is proposed, and the band structure and absorption spectra are analyzed by the use of an eight band k·p model. The structure is based on quantum wells that only support bound states for the valence band. The absence of bound conduction band states has a number of potential advantages, including a reduction of electron trapping and, therefore, a reduction of quantum well induced photocarrier recombination due to reduced spatial overlap of the electron and hole wavefunctions.

Optical properties of tungsten trioxide from first-principles calculations

Tungsten trioxide (WO${}_{3}$) is an Earth abundant material of potential use as a light absorber for solar energy conversion processes. We carried out ab initio calculations of the band structure and absorption spectrum of WO${}_{3}$ using many-body perturbation theory and we present a detailed comparison of our results with photoemission and absorption data. We show that it is necessary to take into account multiple effects, including spin-orbit and electron-phonon interactions and exciton binding in order to correctly predict the measured optical gap. The absorption spectrum obtained by solving the Bethe-Salpeter equation compares well with experiments over a wide energy range, and our calculations correctly account for the redshift observed experimentally upon N${}_{2}$ intercalation in WO${}_{3}$.

First-principle study on the effect of high Ga doping on the optical band gap and the band-edge of optical absorption of ZnO

Based on the density functional theory (DFT), and using the first-principles plane-wave ultrasoft pseudopotential method, we set up models for a pure ZnO and four different concentrations of Ga-doped ZnO, and the geomertry optimization for the four modes was carried out. The total density of states (TDOS), the band structures (BS) and absorption spectrum were also calculated. Results show that the range of Ga doping amount is limited to 2.08 at% to 6.25 at% in this paper; when the doping concentration of Ga increases, the volume change of the system is not obvious; however, when is energy increases, the system will be unstable, the Burstein-Moss effect of its optical band gap will increase, and the absorption spectrum will shift to high energy. The results of calculation agree with the experimental data.

First-principles study on the effect of high Mn doped on the band gap and absorption spectrum of ZnO

According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, we set three different concentration Mn doped ZnO models, and perform the geomertry optimizations for the three modes. The total density of states, the band structures and the optical absorption are also calculated. The results show that in the case of non-spin state, the smaller the doping concentration of Mn is, the smaller the formation energy of ZnO is and the easier the Mn doping is, thus the stabler the crystal struetuer is; the Mn doping leads to the degenerations of the impurity energy band and the conduction band, and also to the optical absorption blue-shift. These calculation results accord with the experimental results. Moreover, the magnetism exists in the system under the situation of spin polarization, the absorption spectrum has a red-shift, which is consistent with the experimental result.