Light Absorption Spectra Research Articles

In situ Measuring Film-Depth-Dependent Light Absorption Spectra for Organic Photovoltaics.

Organic donor–acceptor bulk heterojunction are attracting wide interests for solar cell applications due to solution processability, mechanical flexibility, and low cost. The photovoltaic performance of such thin film is strongly dependent on vertical phase separation of each component. Although film-depth-dependent light absorption spectra measured by non-in situ methods have been used to investigate the film-depth profiling of organic semiconducting thin films, the in situ measurement is still not well-resolved. In this work, we propose an in situ measurement method in combination with a self-developed in situ instrument, which integrates a capacitive coupled plasma generator, a light source, and a spectrometer. This in situ method and instrument are easily accessible and easily equipped in laboratories of the organic electronics, which could be used to conveniently investigate the film-depth-dependent optical and electronic properties.

Effect of hydrogen adsorption energy on the electronic and optical properties of Si-modified single-layer graphene with an Al decoration

The adsorption energy and changes in the structural, electronic, and optical properties of an Al-modified Si-doped single-layer graphene (SLG) structure after hydrogen adsorption were studied using first-principles calculations. The simulation results revealed that the hydrogen adsorption energy of SLG + Si + Al gradually increased to 0.571 eV with an increase in the number of hydrogen molecules. After structural optimization, the C–C bond and the C–Si–C bond angle of SLG + Si + Al regular hexagonal lattice changed within 1.430–1.440 Å and decreased by 29.997°, respectively. In the SLG + Si + Al structure, the resonance of electrons was strengthened, the absorption spectrum of light was enhanced, the width of the absorption peak increased, and electrons absorbed more energy in the transition process.

填补碘空位抑制δ-HC(NH2)2PbI3相以制备高效太阳电池

Formamidinium lead halide (α-FAPbI3) with a broad light absorption spectrum, has recently received considerable attention in optoelectronic applications. However, the FAI-PbI2-DMSO (DMSO: dimethyl sulfoxide) intermediate anisotropic fibers readily form a non-perovskite phase (δ-FAPbI3) and uncontrolled excess PbI2, which hinders the further increase in the efficiencies of solar cells. Caculations indicate that iodine defects in polycrystalline films would enlarge the perovskite tolerance factor and result in the formation of iodide Frenkel defects. Herein, we introduce a post-treatment technique to heal the as-prepared FAPbI3 thin layer and restrain the notorious δ-FAPbI3 through vacancy filling. Furthermore, a new intermediate phase of FAI-PbI2-DMSO-FACl led to a high-quality perovskite layer with an enlarged average grain size that exceeded 2 μm. Consequently, the power conversion efficiencies of FAPbI3 solar cells were significantly enhanced due to the high crystallity of the pure α-phase perovskite. Therefore, this method can be used to obtain high pure-black perovskite films and efficient solar cells.

Au-Mediated Charge Transfer Process of Ternary Cu2O/Au/TiO2-NAs Nanoheterostructures for Improved Photoelectrochemical Performance.

Based on a facile three-step preparation method, Cu2O/Au/TiO2-NAs ternary heterojunction nanocomposites have been successfully synthesized by electrodepositing a Cu2O layer on the surface of Au nanoparticles (NPs) decorated highly ordered TiO2 nanotube arrays (NAs). The structure, surface morphology, chemical composition, and optical and intrinsic defects properties of the as-prepared samples are characterized by transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), UV–vis light absorbance spectra, Raman scattering, and X-ray photoelectron spectroscopy (XPS). Simultaneously, the Cu2O/Au/TiO2-NAs ternary nanohybrids exhibited progressively improved photoelectrocatalytic (PEC) performance compared with the dual Cu2O/TiO2-NAs type-II nanoheterojunctions, confirming by the photocurrent density versus testing time curve (amperometric I–t curve), open-circuit potential versus testing time curve (Voc–t curve), and electrochemical impedance spectroscopy (EIS) measurements, which were mainly ascribed to the synergistic effect of reduced interfacial charge transfer resistance and boosted energetic charge carriers generation associated with embedding Au NPs. Furthermore, the self-consistent charge transfer mechanism of Z-scheme and interband transitions mediated with Au NPs for Cu2O/Au/TiO2-NAs triple nanocomposites is proposed, which was evaluated by nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra excited by 266 and 400 nm, respectively. Following this scheme, UV–vis light photocatalytic activities of Cu2O/Au/TiO2-NAs ternary nanohybrids were elaborated toward photodegradation of methyl orange (MO) in aqueous solution, and the photodegradation rate of optimum triple nanocomplex was found to be 90%.

Endurance degradation of solution-processed ZnO polycrystalline film-based resistive switching memory

Metal oxide-based resistive switching memory cell has potential applications in the next generation of nonvolatile memory devices due to its simple structure, fast reading/writing speed, and good endurance. Zinc oxide (ZnO) is one of excellent resistive switching candidate materials owing to its low-cost, simple preparation process and significant resistive switching characteristics. In this work, homogeneous ZnO precursor solution is spin-coated on indium tin oxide (ITO)-coated glass substrate to deposit a smooth and dense film composed by ZnO nanoparticles with the hexagonal wurtzite structure. Atomic force microscopy images reveal the average grain size of ZnO polycrystalline nanoparticle is about 23.7 nm. An optical band gap of about 3.3 eV is derivate from the ultraviolet-visible light absorption spectra. Current-voltage ( I - V ) curves of Ag/ZnO/ITO memory cells exhibit reversible low-voltage bipolar resistive switching characteristics. Their switching voltages ( V Set/ V Reset) are lower than ± 0.4 V, and the ON/OFF resistance ratio is 103–104 at the read voltage of −0.1 V, which are superior to resistive switching performance of other ZnO polycrystalline films prepared via similar solution methods. However, the memory cell can only maintain 60 stable I - V cycles. After that, the low resistance state gradually degrades to the high resistance state, and the resistive switching memory window completely disappears after 100 I - V cycles. X-ray photoelectron spectra of Zn 2p and O 1s core-levels for ZnO film before and after I - V measurement demonstrate that as-grown film is oxygen-defective ZnO x I - V measurement. Under sustained electric field stress, some drifted oxygen ions combine with oxygen vacancies and change to localized lattice oxygen atoms, this partially remedies the oxygen-deficiency of as-grown non-stoichiometric ZnO x

Electrophysical Properties of Metal Oxide Films Fabricated by Using Spray Pyrolysis

This document describes the technology of manufacturing metal oxide films ZnO, SnO2, Zn2SnO4 from aqueous solutions of the corresponding salts by spray pyrolysis. The modes and conditions of deposition of metal oxide films on hot (420 °C) glass substrates are given. The electrical parameters of the films were measured by the van der Pau method and by the Hall effect, the surface resistance was in the range from 140 to 85⋅103 Ohm/. The band gap was determined by light absorption spectra and was within 3.2...3.5 eV. For all metal oxides, the n-type conductivity was determined using the thermosonde and the Hall effect.

Photometric determination of rhenium in mixed hydrochloric-nitric acidic solutions formed upon processing of molibdenite concentrate

The results of spectrophotometric study of the system Re (VII) – HNO 3 – HCl – mercaptoacetic acid – Sn (II) are used to develop a sensitive and selective method of photocolorimetric determination of rhenium in acid nitrate-sulfate solutions formed upon decomposition of molybdenite concentrates with nitric acid and also to reveal trends in complexation of aliovalent rhenium with organic sulfur ligands. Ammonium perrhenate (AR-0) was purified on a Purolite C-100 cation exchanger. Solutions of mercaptoacetic (thioglycolic) acid were prepared from chemically pure Apolda chemical (Germany). Light absorption spectra were recorded on EPS-3T (Hitachi, Japan) and Specord M-40 (Carl Zeiss Jena, Germany) spectrophotometers; the optical density of the solutions was recorded on a KFK-2 (Russia) photocolorimeter. Optimal conditions for the formation of a colored complex compound with mercaptoacetic acid in a mixed hydrochloric-nitric acid solution were determined along with the composition and stability of the complex. The mechanism of redox reactions that occur during complexation is proposed. A technique for monitoring the rhenium content in the products of hydrometallurgical processing of molybdenite concentrates is developed. The procedure provides rhenium determination in the presence of accompanying elements (Mo, Cu, Fe, Ni, etc.) and oxidizing agents (>120 g/liter The developed procedure includes preliminary separation of molybdenum and other interfering impurities by selective sorption of ions on a strongly basic anionite (ChFO) followed by their desorption with a 5 M HNO 3 solution and subsequent photocolorimetric determination of rhenium in the eluate in the form of an orange-yellow (λ max = 460 nm) mixes-ligand complex of Re (III) of assumed composition [Re(L) 3 NOCl]–, where L — is mercaptoacetic acid anion. The developed method of rhenium determination was used in analysis of effluents of washing sulfuric acid taken from the sulfuric acid workshop of the copper smelting plant of Almalyk MMC JSC (Uzbekistan).

Visible-Light Active Photocatalytic Dual Layer Hollow Fiber (DLHF) Membrane and Its Potential in Mitigating the Detrimental Effects of Bisphenol A in Water

The presence of bisphenol A (BPA) in various water sources has potentially led to numerous adverse effects in human such as increased in blood pressure and derangement in liver function. Thus, a reliable treatment for the removing BPA is highly required. This present work aimed to study the efficiency of visible light driven photocatalytic dual-layer hollow fiber (DLHF) membrane for the removal of BPA from water and further investigated its detrimental effects by using an in-vivo model. The prepared membranes were characterized for their morphology, particles distribution, surface roughness, crystallinity and light absorption spectra. The removal of 81.6% and 86.7% in BPA concentration was achieved for N-doped TiO2 DLHF after 360 min of visible and UV light irradiation, respectively. No significant changes for all three groups were observed in liver function test meanwhile the rats-exposed to untreated BPA water shows significance blood pressure increment contrary to rats-exposed to treated BPA water. Similarly, the normal morphology in both jejunum and ileum were altered in rats-exposed to untreated BPA water group. Altogether, the presence of N-doped TiO2 in DLHF are shown to significantly enhance the photocatalytic degradation activity under visible irradiation, which effectively mitigates the effect of BPA in an in-vivo model.

Time-Dependent Density Functional Theory Investigation of the UV–Vis Spectra of Organonitrogen Chromophores in Brown Carbon

The ability of brown carbon (BrC) in aerosols to absorb solar radiation is an important but highly uncertain factor in climate forcing. The uncertainties are partially due to incomplete characterization of BrC chromophores and lack of authentic standards to confirm light absorption. Organonitrogen species are crucial components in atmospheric aerosols, but their light-absorbing properties remain to be fully characterized. To facilitate the molecular characterization of BrC chromophores, time-dependent density functional theory (TD-DFT) based computational chemistry approaches were used in this study to predict the light absorption spectra of 16 organonitrogen species, including nitroaromatics, nitro-heterocyclic compounds, organonitrates, and Maillard-type reaction products in BrC. Effects of basis sets, functionals, solvation, and pH on light absorption properties of these compounds were evaluated. Predicted absorption spectra were compared with experimental measurements. Overall, the PBE0 and B3LYP functionals tend to outperform PBE and CAM-B3LYP on the predicted absorption spectra of studied compounds. Absorbance calculated in water and methanol (bulk solvents) varies up to 2 nm (0.03 eV). Absorbance calculated in gas phase (vacuum state) blue-shifts in comparison to solvation. Absorbance of weak acids (e.g., nitrophenols) is enhanced under basic conditions, and the absorption spectra can be predicted by the fractions of conjugate acid–base species. Results from this study demonstrate that a combined use of TD-DFT predictions and experimental measurements of light absorption can allow for a rapid and reliable determination of potential chromophores in BrC when authentic standards are not available.

Mixedligand complexes of uranium (VI) with dithiolophenols and hydrophobic amines in photometric analysis

AbstractIn this paper we studied the interaction of uranium (VI) with with dithiolphenols (2,6‐dithiophenol, 2,6‐dithiol‐4‐methylphenol, 2,6‐dithiol‐4‐ethylphenol, 2,6‐dithiol‐4‐tert‐butylphenol), and hydrophobic amines by absorption spectroscopy method. The sudied hydrophobic amines are aniline, N–methylaniline, N,N–dimethylaniline, diphenylguanidine, triphenylguanidine, benzylamine, phenantrolin, dipyridyl, p‐aninopyridin, 2‐(N,N‐dimethylaminomethyl)‐4‐methylphenol and 2‐(N,N‐dimethylaminomethyl)‐4‐bromphenol. The optimal conditions for the formation and extraction of ionic associates were found and the ratios of components in the complexes were established. It was found that associates are formed in a weakly acidic medium (pHopt = 3.5‐7.1). The maxima in the light absorption spectra are observed at λ = 434‐478 nm. Molar coefficient of absorption is equal ε = (2.65‐3.62)•104. On the basis of the obtained data, photometric methods of uranium determination in various objects have been developed.

Light entrainment of retinal biorhythms: cryptochrome 2 as candidate photoreceptor in mammals.

The mechanisms that synchronize the biorhythms of the mammalian retina with the light/dark cycle are independent of those synchronizing the rhythms in the central pacemaker, the suprachiasmatic nucleus. The identity of the photoreceptor(s) responsible for the light entrainment of the retina of mammals is still a matter of debate, and recent studies have reported contradictory results in this respect. Here, we suggest that cryptochromes (CRY), in particular CRY 2, are involved in thatlight entrainment. CRY are highly conserved proteins that are a key component of the cellular circadian clock machinery. In plants and insects, they are responsible for the light entrainment of these biorhythms, mediated by the light response of their flavin cofactor (FAD). In mammals, however, no light-dependent role is currently assumed for CRY in light-exposed tissues, including the retina. It has been reported that FAD influences the function of mammalian CRY 2 and that human CRY 2 responds to light in Drosophila, suggesting that mammalian CRY 2 keeps the ability to respond to light. Here, we hypothesize that CRY 2 plays a role in the light entrainment of retinal biorhythms, at least in diurnal mammals. Indeed, published data shows that the light intensity dependence and the wavelength sensitivity commonly reported for that light entrainment fits the light sensitivity and absorption spectrum of light-responsive CRY. We propose experiments to test our hypothesis and to further explore the still-pending question of the function of CRY 2 in the mammalian retina.

Black phosphorus @ molybdenum disulfide 2D nanocomposite with broad light absorption and high stability for methylene blue decomposition photocatalyst

Recently, black phosphorus (BP) has become an increasingly popular two-dimensional material with application in many fields. In the field of photocatalyst, the substance is attracted by a wide spectrum and abundant constituents. BP is an attractive material with unique properties owing to its anisotropic structure, which is favorable for catalyst design as a result of bandgap change based on thickness. However, it has proved problematic in the photocatalyst field, due to rapid recombination of electrons and holes. As a result, to overcome this, we used a complex with MoS2 to prevent the recombination of electrons and holes and to have a broad range of optical absorption from visible light to NIR. MoS2 nanoflakes are a two-dimensional (2D) material of the transition metal dichalcogenide family, the advantage of which is that it can be used as a nano-junction between 2D materials. The nanocomposite material of BP and MoS2 shows a remarkable increase in photocatalytic decomposition ability of methylene blue which is an organic dye. It also has many cycles of catalytic ability, which is advantageous in terms of stability. There are expectations that MoS2 @ BP photocatalysts will be widely applied as a non-precious metal photocatalyst with broad light absorption spectra and multi-function photocatalytic materials.

"Брэгговская" решетка заселенности электронов, наводимая в гетероструктуре Al-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-As-GaAs-Al-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-As ее собственным стимулированным пикосекундным излучением

It was shown that the modulation of the spectrum of stimulated picosecond emission generated in the AlxGa1-xAs–GaAs–AlxGa1-xAs waveguide heterostructure upon optical pumping of GaAs, and a number of previous experimental results become explainable under the assumption that emission forms a symmetric modification of the “Bragg” population lattice of nonequilibrium electrons GaAs. Boundary conditions defining the lattice design are proposed. In particular, in order to satisfy them, the lattice can only change discretely. The latter is consistent with a change in the modulation of the light absorption spectrum in GaAs, which reflects the modulation of population depletion created by emission in a high-quality heterostructure. The latter is consistent with a change in the modulation of the light absorption spectrum in GaAs, which reflects the modulation of population depletion created by emission. Inducing the lattice, i.e. burning out spatial holes, is one of the reasons for the multimode nature of emission, competition and switching of its modes, modulation of the gain spectrum (burning out frequency holes). The same is possible in a semiconductor laser, as in a waveguide.

Recent developments and perspectives in CdS-based photocatalysts for water splitting

Over the past decades, visible-light-driven water splitting on CdS has gained substantial attention owing to its low cost, appropriate bandgap, and electron affinity that best fit the visible light absorption spectrum.

Identification of Bioactive Phytochemicals in Mulberries.

Mulberries are consumed either freshly or as processed fruits and are traditionally used to tackle several diseases, especially type II diabetes. Here, we investigated the metabolite compositions of ripe fruits of both white (Morus alba) and black (Morus nigra) mulberries, using reversed-phase HPLC coupled to high resolution mass spectrometry (LC-MS), and related these to their in vitro antioxidant and α-glucosidase inhibitory activities. Based on accurate masses, fragmentation data, UV/Vis light absorbance spectra and retention times, 35 metabolites, mainly comprising phenolic compounds and amino sugar acids, were identified. While the antioxidant activity was highest in M. nigra, the α-glucosidase inhibitory activities were similar between species. Both bioactivities were mostly resistant to in vitro gastrointestinal digestion. To identify the bioactive compounds, we combined LC-MS with 96-well-format fractionation followed by testing the individual fractions for α-glucosidase inhibition, while compounds responsible for the antioxidant activity were identified using HPLC with an online antioxidant detection system. We thus determined iminosugars and phenolic compounds in both M. alba and M. nigra, and anthocyanins in M. nigra as being the key α-glucosidase inhibitors, while anthocyanins in M. nigra and both phenylpropanoids and flavonols in M. alba were identified as key antioxidants in their ripe berries.

Investigating the Photocatalytic Performances of Nanocomposites Containing Narrow‐band‐gap Copolymers and ZnO†

AbstractComposites of ZnO and conjugated polymers find applications in removal of polluting dyes from industrial wastes. The choice of functionality and repeating unit of polymer is important to improve the efficacy of the process. While heterocyclic diketopyrrolopyrrole (DPP) ‐based polymers are often considered as the most promising donor moiety in traditional bulk heterojunction solar cell devices, benzothiadiazole‐based polymers are reported to show the best performance as photosensitizer for dye degradation. In this paper, we report for the first time the preparation of copolymers containing both the above mentioned heterocyclic repeating units linked directly or by a double bond. We were delighted to observe broad spectrum of substantial light absorption from UV to NIR range and a low band gap for one of the polymers, the main reason behind higher efficacy in dye removal under sunlight. Finally, we studied the efficacy of the polymers as photosensitizer for ZnO promoted dye degradation process which showed almost a complete degradation of a model dye only within two hours, one of the best results reported recently using the conjugated polymers.

Study of Uranium(VI) Complexation with Dithiolphenols and Hydrophobic Amines

The interaction of uranium(VI) with editionpanorama (2,6-dithiolphenol, 2,6-dithiol-4-methylphenol, 2,6-dithiol-4-ethylphenol, 2,6-dithiol-4-tert-butylphenol) and hydrophobic amines has been studied by absorption spectroscopy. Hydrophobic amines used are aniline, N–methylaniline, N,N-dimethylaniline, diphenylguanidine, triphenylguanidine, benzylamine, phenantrolin, dipyridyl, p-aninopyridin, 2‑(N,N-dimethylaminomethyl)-4-methylphenol, and 2-(N,N-dimethylaminomethyl)-4-bromphenol. The optimal conditions for the formation and extraction of ionic associates are found and the ratios of components in the complexes are determined. It has been found that associates are formed in a weakly acidic medium (pHopt 3.5–7.1). The maxima in the light absorption spectra are observed at λ = 434–478 nm. Molar coefficient of absorption is equal to e = (2.65–3.62) × 104. On the basis of the obtained data, photometric methods of uranium determination in various objects have been developed.

Effects of hydroxyl groups and hydrogen passivation on the structure, electrical and optical properties of silicon carbide nanowires

The effects of hydrogen and hydroxyl passivation on the structure, electrical and optical properties of SiCNWs were investigated. The passivation performance of different atoms (groups) were discussed by analyzing the distribution of electronic states and the polarity of chemical bonds. The results show that passivation can improve the stability of SiCNWs structure, and the effect of hydroxyl is better than hydrogen passivation. And hydrogen and hydroxyl passivation both increase the band gap of SiCNWs, and the changing trend of band gap is relevant to the polarity of the covalent bond formed by the passivation of surface atoms. Moreover, passivation enhances the stability of the optical properties of SiCNWs, resulting in narrowing of light absorption, photoconductivity and other spectra, and the response peak shifts to the deep ultraviolet region, which means that hydrogen or hydroxyl passivation of SiCNWs is likely to be a candidate material for deep ultraviolet micro-nano optoelectronic devices.

Cyclotron resonance inside the Mott gap: A fingerprint of emergent neutral fermions

A major obstacle to identify exotic quantum phases of matter featuring spin-charge separation above one-dimension is the lack of tailored probes allowing to establish their presence in correlated materials. Here we propose an optoelectronic response that could allow to pinpoint the presence of certain spin-charge separated states with emergent neutral gapless fermions in two and three-dimensional materials. We show that even though these states behave like insulators under static electric fields, they can display clear cyclotron resonance peaks in their light absorption spectrum under static magnetic fields, but typically the principal Kohn mode will be missing in comparison to ordinary metals. This distinctive phenomena could be tested in materials such as triangular lattice organics, three-dimensional mixed valence insulators YbB$_{12}$ and SmB$_6$, and transition metal dichalcogenides 1T-TaS$_2$ and 1T-TaSe$_2$.

Improve the quality of HC(NH2)2PbIxBr3−x through iodine vacancy filling for stable mixed perovskite solar cells

Formamidinium-based (FA-based) with broader light absorption spectra have been attracted enormous attention. However, the FAI-PbI2-DMSO intermediate anisotropic fibers can easily produce yellow δ-FAPbI3 and uncontrolled excess PbI2, which significantly increased the defect and reducing the reproducibility of devices. Furthermore, the iodine defect in polycrystalline films would enlarge the perovskite tolerance factor and trigger ion migration. This ion migration within perovskite layer leads to device degradation and impedes large scale commercial applications. Herein, we develop a vacancy filling (VF) method to repair iodine vacancy as well as yield pure black phase FA perovskite. Upon post treatment with FABr, the point defects on surface and the notorious δ-FAPbI3 caused by lager tolerance are removed though vancancy fulling. The champion of obtained FAPbIxBr3−x device presents the power conversion efficiency (PCE) up to 18.2% and could remain >85% of the original PCE after 20 days in the dark at room temperature (10–25 °C) and humidity of 10–40%. Therefore, this VF technique provides an interesting entry for obtaining high pure black perovskite phase.