Absorption In Region Research Articles

Calculation of the Density of the Distribution of Electronic States in the Conduction Band from the Fundamental Absorption Spectra of Amorphous Semiconductors

The region of fundamental absorption in the optical spectra of amorphous semiconductors is theoretically studied using the Davis-Mott approximation according to the Kubo-Greenwood formula. As is known, three types of optical transitions of the electron can be observed in the fundamental absorption region; from the tail of the valence band to the conduction band, from the valence band to the conduction band and from the valence band to the tail of the conduction band. For all these electronic transitions, analytical expressions of the partial absorption spectra are obtained from two different types of the Kubo-Greenwood formula. The width of the optical mobility gap and the proportionality coefficient were determined in the analytical form of the interband absorption spectrum by fitting them to the experimental interband absorption spectrum. A new method is presented for calculating the density of distribution of electronic states in the conduction band of amorphous carbon based on the experimental interband absorption spectrum and the analytical expression of the Kubo-Greenwood formula written for the interband absorption spectrum.

Novel 1,2,4-triazole sensitizers using N-arylsydnone as Synthon: Synthesis, Spectral, electrochemical, DFT and photovoltaic properties

Two novel 1,2,4-triazolone derivatized triphenylamine (TPA) and phenothiazine (PTZ) based metal-free organic dyes have been designed, synthesized and anchored on 1D CdS nanowires to serve as photoelectrochemical (PEC) dye-sensitized solar cells (DSSCs). Solution chemistry is employed simply and efficiently to link cadmium sulfide nanowires (CdS NWs) into a nano-network. Optical, electrochemical and density functional theory (DFT) have been well utilized to examine the properties of synthesized dyes (TPA and PTZ). In the visible range, sensitizer-anchored CdS NWs exhibit a wider region of light absorption referenced to naked CdS NWs. Comprehensive photovoltaic assessment showed that TPA and PTZ devices respectively showed IPCE 3.02 and 3.13 times more efficient than bare CdS NWs under standard sunlight (100 mW/cm2, AM 1.5G) illumination. The collected findings offer solid evidence for the existence of increasing external quantum efficiency (EQE) and exhibit good agreement with the optical experiments.

One sight on sound generation and absorption by vortices

Vortices generate sound and absorb sound. A. Powell and M. S. Howe deduced the equations and showed that the exterior product of vortex and local velocity took part in sound generation and absorption. However, it is difficult to image its physical phenomena. In this paper, as one example, the interaction of sound and vortices at the throat of a cavity with grazing flow is investigated by CFD simulation. As the results, it is found that sound absorbing regions and sound generating regions are locally distributed and moving. It is also found that when counterclockwise vortices turn to the left, they absorb sound and when they turn to the right, they generate sound. Based on these results, 'Floating Vertical Bar Model (FVB Model)' is proposed to image the sound generation and absorption phenomena, in which a vortex is simulated as a bar floating vertically on the water surface, because a vortex has coherent structure along its axis like a bar. When a vortex (a bar) is accelerated perpendicular to its axis, pressure fluctuation (water wave) is easily generated. And when sound wave (water wave) shakes a vortex (a bar), sound energy is absorbed by a vortex (a bar) motion.

Electrochemical analysis of thermally treated two dimensional zinc sulphide hexagonal nano-sheets with reduced band gap

Significantly reduced band gap (2.0 eV) zinc sulphide (ZnS) nanoparticles are synthesized using microwave/ultraviolet/ultrasonic assisted hydrothermal route in a two step process. Initially, ZnS nanospheres are synthesized, showing a cubic structural phase with a band gap of 3.2 eV, which is further annealed at 1000 °C to get the final product. Following annealing, the cubic ZnS undergoes a phase change to wurtzite ZnS, in the form of hexagonal nanosheets showing polymorphism phenomena, along with a reduced band gap of 2 eV. The optical analysis reveals a red shift in the absorbance region, transitioning from the absorption of UV radiations in cubic ZnS to visible radiations in wurtzite ZnS. Thermogravimetric (TGA) measurements and its analysis also revealed the phase change of ZnS (cubic) to ZnS (Wurtzite) when heated at 1000 °C. Microstructural analysis reveals the formation of sheets oriented along (100) plane, which is evidenced by the interplanar spacing and lattice fringes. The photoluminscence spectra highlights quantum energy states present between the highest occupied molecular orbital (HOMO), which is 2.36 eV for cubic phase and 1.76 eV for the hexagonal phase, and the lowest unoccupied molecular orbital (LUMO), with values of −0.84 eV for cubic while −0.24 for hexagonal ZnS. The CIE coordinates for wurtzite ZnS, at X= 0.55 and Y= 0.23, corresponds to red light emission. The suitability of wurtzite phase ZnS for solar cell applications has been demonstrated through electrochemical studies using Nyquist plot and cyclic voltrammetry (CV) techniques. CV demonstrates the presence of redox peaks and reversibility of the material during the redox process. The diffusive behaviour is also confirmed by observing the variation of peak current with scan rate, following Rendle Sevick equation. The presence of Warburg diffusion in Nyquist plot indicates the efficient charge transfer dynamics of the material, suggesting a high potential for exciton formation in energy production. Consequently, this material stands as a promising candidate for efficient solar cells.

Toward soluble high-performance electrochromic polymer: Optimizing cross-link density

Cross-linked conjugated polymers attract great attentions in optoelectronic field due to their unique properties resulting from the existence of intramolecular pore and network structure. However, the poor solubility restricts the application of cross-linked polymers in photoelectric device. Here, the strategy of changing cross-link density is employed to optimize solubility and properties of cross-linked conjugated polymer. Five polythiophene derivatives with different cross-link densities were synthesized through direct arylation reaction. The cross-linked conjugated polymers achieve good solubility in organic solvent through decreasing cross-link density, and possess similar optical absorption regions compared to conjugated polymer without cross-linked structure. Through optimizing cross-link density, the electrochromic properties of conjugated polymers could be enhanced, including optical contrast (55 %), response time (0.6 s), coloration efficiency (CEox = 510 cm2 C-1; CEred = 3567 cm2 C-1), and stability, which is more excellent than that of reported cross-linked polymers. And, the flexible electrochromic device based on PET-(1,9) was constructed by simple solution processing and could achieve fast color change between wine red and light blue in low voltage driving force, which indicating the applicability of soluble cross-linked conjugated polymer. Besides, the mechanism about ionic transport and stability improvement of cross-linked conjugated polymers is discussed. These results demonstrate that changing cross-link density is an effective strategy to optimize the properties of cross-linked conjugated polymers.

Synergetic enhancement effect of two-dimensional MoS2 nanosheets and metal organic framework-derived porous ZnO nanorods for photodegradation performance.

Two-dimensional transition metal dichalcogenides and semiconductor metal oxides have shown great potential in photocatalysis. However, their stability and efficiency need to be further improved. In this paper, porous ZnO nanorods with high specific surface area were prepared from metal-organic framework ZIF-8 by a simple hydrothermal method. A MoS2/ZnO composite was constructed by loading MoS2 onto the surface of porous ZnO nanorods. Compared with ZnO materials prepared by other methods, MoS2/ZnO prepared in this paper exhibits superior photocatalytic performance. The enhanced photocatalytic activity of the MoS2/ZnO composite can be attributed to the formation of heterojunctions and strong interaction between them, which greatly facilitate the separation of electrons and holes at the contact interface. In addition, due to the wide absorption region of the visible spectrum, MoS2 can greatly broaden the light absorption range of the material after the formation of the composite material, increase the utilization rate of visible light, and reduce the combination of electrons and holes. This study provides a new way to prepare cheap and efficient photocatalysts.

Preparation of PbBiO2I ultrathin nanosheets with rich oxygen vacancies for enhanced visible-light-driven photocatalytic activities

Photocatalytic oxidation technology is deemed as a prospective approach to settle the global environmental crisis. Nevertheless, the photocatalytic performance is limited by the insufficient solar light harvesting ability and disappointing charge carrier separation efficiency of photocatalysts. Herein, PbBiO2I ultrathin nanosheets with tunable oxygen vacancy (OV) concentrations were successfully fabricated via ionothermal process. The crystal structure, morphology and photoelectrochemical properties of the acquired catalysts were systematically studied. The photocatalytic degradation results demonstrate that rich oxygen vacancy (ROV) PbBiO2I possesses the highest photocatalytic degradation activity, which is about 2.9 and 35.0 times higher than those of deficient oxygen vacancy (DOV) PbBiO2I and bulk PbBiO2I in rhodamine B (RhB) degradation. The enhanced visible-light absorption region arising from bulk oxygen vacancy and surface oxygen vacancy can serve as highly active sites for catalytic reaction. This contributes to enriching electrons to accelerate oxygen molecular activation and boost charge separation. Additionally, superoxide radicals (O2•-) and holes (h+) are proved to be the major reactive species during photocatalytic process. By which, a feasible photocatalytic mechanism was primarily proposed. This research can offer a new avenue for developing bismuth-based defective photocatalyst in the field of environmental remediation.

Ammonia induced strong LSPR effect of chain-like ATO nanocrystals for hyperspectral selective energy-saving window applications

Sb-doped SnO2 (ATO) is a promising multifunctional material with great potentials for practice applications, however, it suffers from poor absorption efficiency of near-infrared (NIR) light due to its relatively weak localized surface plasmon resonance (LSPR) effect. In this study, a series of chain-like ATO nanocrystals (NCs) with high Sb5+/Sb3+ ratio(s) and oxygen defect concentration were precisely prepared by a simple but efficient precipitation-hydrothermal method. The introduction of NH3 served as a double-hero in controlling both the solution pH and the shape of nanocrystals. Both experimental and theoretical calculation results have indicated that our synthesis strategy effectively increases the free carrier concentration and mobility of ATO NCs to improve LSPR effect, and thereby effectively broaden the NIR light absorption region and improve the absorption capacity. Furthermore, the as-prepared ATO hydrosols show great potentials for practical applications in energy-saving building since a flexible application mode as an energy-saving window can be implemented. Both the formation of ATO hydrosol windows by pouring into the laminated glass and spin-coating onto the flat glass to create ATO coatings can result in excellent optical properties and thermal insulation performance. These findings may not only accelerate the commercialization process of ATO but also provide valuable theoretical guidance for developing novel hyperspectral materials.

Construction of a novel double S-scheme heterojunction CeO2/g-C3N4/Bi2O4 for significantly boosted degradation of tetracycline: Insight into the dual charge transfer mode

Constructing dual S-scheme heterojunction, as one kind of new strategy for the reinforcement of photocatalytic property, shows significant advantages in facilitating the migration of photoinduced charges and achieving high redox potentials. Herein, a novel double S-scheme heterojunction CeO2/g-C3N4/Bi2O4 was designed and synthesized successfully. The photodegradation of tetracycline (TC) over CeO2/g-C3N4/Bi2O4 was carried out under the irradiation of visible light. The double S-scheme interfacial charge transmission mode of CeO2/g-C3N4/Bi2O4 was investigated according to Fermi level, band structure, and the in-depth analysis of in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and electron spin resonance (ESR) spectra. The CeO2/g-C3N4/Bi2O4 exhibits excellent catalytic activity with a high TC removal efficiency of 94 % and a remarkable mineralization efficiency of 51 %. The rate constant (0.05811 min−1) of TC degradation for CeO2/g-C3N4/Bi2O4 is 12.9, 7.8, 4.3, 2.2, and 3.1 times those for g-C3N4, CeO2, Bi2O4, g-C3N4/Bi2O4 and CeO2/g-C3N4, separately. The prominently boosted activity may be due to two factors. Firstly, the successful creation of the double S-scheme electron migration channel greatly boosts the transmission of photogenerated carriers, represses the recombination of electrons with holes, and ensures the strongest redox potential of CeO2/g-C3N4/Bi2O4. Secondly, the introduction of Bi2O4 with excellent visible-light absorption broadens the optical absorption region of CeO2/g-C3N4/Bi2O4. Additionally, the influence of the typical environmental factors (pH, inorganic anions, cations, and natural humus) on the photodegradation of TC was explored. The three probable pathways for TC degradation were inferred via analyzing intermediates. The current work offers a novel outlook for enhancing the activity of ternary heterojunction photocatalysts applied in environmental restoration.

Electronic structure and optical properties of superconducting compounds ScGa3 and LuGa3

The optical properties of bulk AuCu3-type ordered superconducting binary compounds ScGa3 and LuGa3 have been experimentally investigated for the first time in the wide spectral range and explained in terms of the band structure. First-principles calculations of electronic densities of states and optical conductivities are performed within the framework of LSDA+U method using the LMTO-ASA software package. The measured dielectric functions spectra for both materials exhibit a strong absorption region above ∼ 1[Formula: see text]eV, which are in a reasonable agreement with the calculated metal-like energy structures of compounds. Features of quantum light absorption are discussed on the basis of a comparative analysis of experimental and theoretical spectra of interband optical conductivity. Plasma and relaxation frequencies of conduction electrons are determined.

The Impact of Model Resolution on the Southern Hemisphere in Community Climate System Model Version 4 Idealized Climate Simulations

Model resolution plays a large role in accurately simulating the Southern Hemisphere circulation in both the ocean and atmosphere. Resolving the mesoscale field is important as it has been shown to have a significant impact on the large-scale climate in eddy-rich regions, which are regions of large CO2 absorption. The presence of ocean and atmospheric mesoscale features can affect sea surface temperatures, the strength and location of storm tracks, and many other air-sea processes. Additionally, with an improvement in resolution, the eddy kinetic energy in the ocean can be expected to change considerably. The significance model resolution has on the Southern Hemisphere is examined using the Community Climate System Model, Version 4, eddy-parameterizing and eddy-resolving simulations. The CO2 concentrations and ozone levels are specified independently to better understand how the mesoscale field responds to extreme changes in external forcing and the resulting climate impacts. Overall, in the eddy-parameterizing simulations, the ozone forcing is found to be more important than the changes in CO2 concentrations. However, in the case of the eddy-resolving simulations, the CO2 concentrations are found to be more dominant, especially in eddy-rich regions. These results demonstrate the need for an increase in model resolution for climate prediction.

Assisted assembling of Bi2WO6/rGO composites: A 3D/2D Hierarchical nanostructures for enhanced photocatalytic water remediation and photo-(electro)catalytic water splitting proficiency

The current study explores the possibility of effectively improving Bi2WO6 (BWO) nanostructures in photocatalytic clean H2 generation and treating water from pharmaceutical wastes. BWO nanoparticles (NPs) hybridized with carbon-derived materials proved to be an efficient candidate in the field of photocatalysis. In this work, BWO nanostructures have been synthesized via the facile co-precipitation technique. The reduced graphene oxide (r-GO) was used as the carbon derivative for the hybridization process. Furthermore, different weight percentages of rGO were loaded with BWO NPs through the wet impregnation technique. The structural, and morphological analysis confirmed the formation of BWO/x% rGO composites. UV-DRS analysis showcased the reduction in bandgap in annexure with increased light absorbance region upon rGO inclusion. Time-resolved photoluminescence (TRPL) proved a prolonged lifetime for BWO/15% rGO composite. In addition, their photocatalytic abilities were put to the test, and BWO/15% rGO nano-hybrid demonstrated a superior degradation of pharmaceutical wastes like tetracycline hydrochloride (TCH) and levofloxacin (LVX) from water in 15 min. Furthermore, photo-electrochemical measurements showed the lowest onset potential and better charge transfer for efficient splitting of water. The photocatalytic water splitting was performed in the presence of sacrificial agents and in the absence of sacrificial agents, where BWO/15% rGO exhibited maximum H2 evolution.

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages

AbstractChiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host–guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R‐PAC‐2, S‐PAC‐2 (with Br substituents) and R‐PAC‐3, S‐PAC‐3 (with CH3 substituents) enantiomers. PAC‐2, rather than PAC‐3, achieves fullerene encapsulation and selective binding of C70 over C60 in fullerene carbon soot. More significantly, the occurrence of chiral induction between R‐PAC‐2, S‐PAC‐2 and fullerenes is confirmed by single‐crystal X‐ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face‐to‐face arene‐fullerene interactions dominate C70 selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages.

Chiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host-guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R-PAC-2, S-PAC-2 (with Br substituents) and R-PAC-3, S-PAC-3 (with CH3 substituents) enantiomers. PAC-2, rather than PAC-3, achieves fullerene encapsulation and selective binding of C70 over C60 in fullerene carbon soot. More significantly, the occurrence of chiral induction between R-PAC-2, S-PAC-2 and fullerenes is confirmed by single-crystal X-ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face-to-face arene-fullerene interactions dominate C70 selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.

Introducing thiazole units into small-molecule acceptors for efficient non-fullerene organic solar cells

The end-group modification engineering has been widely applied in non-fullerene acceptors (NFAs) to achieve high-performance organic solar cells (OSCs). Herein, we designed and synthesized a series of small-molecule acceptors (SMAs), namely ODTz-γ, ODTz-m, DTTz-γ and DTTz-m, which containing the electron-withdrawing thiazole units on the end groups at different position. These SMAs not only exhibited strong and broad absorption region from 500 nm to 900 nm, identical band gaps, but also the similar energy levels, indicating the position of thiazole units have trivial effect on their absorbance and energy levels. OSCs were fabricated by integrating an electron-donating polymer PBDB-T with these resultant electron-accepting materials. Devices based on ODTz-γexhibited an obviously higher power conversion efficiency over 12.0%, which outperformed those of obtained from devices based on other SMAs. Further characterization of the devices revealed that introducing the thiazole units into the γ position of end groups can enhance the charge transport mobility, suppress recombination, and improve the blend film morphology.

Enhancement in the light-stability of BAPO and ITX-based photo-curable materials via photobleaching of pyrrolidene cyclohexanone

In this study, it was proved that the light-stability of bis(2,4,6-trimethyl benzoyl) phenyl phosphonate(BAPO) and isopropyl thioxanthone(ITX)-based photocurable materials was improved by adding the solution mask (E)-1-cyclohexyl-3-(1H-pyrrol-2-yl)-prop-2-en-1-one(E-CPP), which was resulting from the BAPO/ITX light absorption inhibition by E-CPP's wider absorption region and larger molar extinction coefficient. In addition, BAPO/ITX can be reactivated to absorb light for photopolymerization when E-CPP fades under high-intensity irradiation of LED@405 nm. The relevant mechanism was finally verified and proposed.

A novel multifunctional magnetically recyclable BiOBr/ZnFe2O4-GO S-scheme ternary heterojunction: Photothermal synergistic catalysis under Vis/NIR light and NIR-driven photothermal detection of tetracycline

The threat of tetracycline (TC) to human health has become a significant issue that cannot be disregarded. Herein, in order to achieve effective degradation and high-sensitivity detection of TC, BiOBr/ZnFe2O4-GO (BOB/ZFO-GO) S-scheme heterojunction nanocomposites (NCs) have been prepared using hydrothermal method. GO with high light absorption capacity accelerated the electron transfer between BiOBr and ZnFe2O4 nanocrystals and extended the light absorption region of BOB/ZFO NCs. The optimal GO addition of BOB/ZFO-GO NCs could degrade TC solution of 10 mg/L in 80 min and have a high reaction rate constant (k) of 0.072 min−1 under visible/NIR light. According to calculations, the non-metal photocatalyst (BOB/ZFO-GO(2)) with the best degradation performance had a photothermal conversion efficiency of up to 23%. Meanwhile, BOB/ZFO-GO NCs could be recycled by magnetic field. The excellent photocatalytic and photothermal performance could be maintained even after several cycles. In addition, a photothermal detection sensor based on a photothermal material/specific recognition element/tetracycline sandwich-type structure was constructed for the trace detection of TC concentration with a detection limit as low as 10-4 ng/mL. This research provides a unique idea for the multi-functionalization of photocatalysts and has a wide range of potential applications for the identification and treatment of organic wastewater.

Effects of 63 MeV proton irradiation on the performance of MWIR InGaAs/InAsSb nBn photodetectors

An investigation into the effects of 63 MeV proton irradiation on high-sensitivity mid-wave infrared InGaAs/InAsSb nBn devices is performed. Three different structures with various absorber region doping profiles are irradiated and characterized to assess their impact on performance degradation. Minority carrier lifetime is measured using time-resolved photoluminescence and lifetime damage factors are assessed. The majority carrier concentration is determined via capacitance–voltage measurements and dopant introduction rates are calculated. An analysis of dark current density is performed using these material parameters, revealing a reduction in mobility with proton fluence and the emergence of a proton-induced trap energy level. Quantum efficiency is calculated at each proton fluence, and quantum efficiency damage factors show that the graded doping structure exhibits the least reduction of quantum efficiency with dose, attributed to its effective mobility enhancement. Conclusively, detector sensitivity, assessed via shot-noise limited noise-equivalent irradiance, shows that the graded doping structure is the least susceptible to high energy proton irradiation-induced performance degradation.

Daul Z-scheme heterojunction BiOBr/Bi2O2.33/g-C3N4 for enhanced visible-light-driven tetracycline hydrochloride degradation

The construction of heterojunction photocatalysts with superior visible light photocatalytic performance is an effective strategy to addressing antibiotic pollution. A dual Z-scheme heterojunction BiOBr/Bi2O2.33/g-C3N4 was synthesized via hydrothermal and calcination methods, exhibiting exceptional degradation TC-HCL efficiency under visible light irradiation. The well-designed heterojunction was comprehensively supported by SEM, XPS, XRD and other series of characterization. Moreover, the BBCN50 heterojunction demonstrated an optimal degradation efficiency of 97.0% in 60 min compared to BB and CN with efficiencies of 90.8% and 70 respectively. The superior photocatalytic performance is attributed to the significantly broadened visible light absorption region and enhanced migration and separation of photogenerated electron-hole pairs facilitated by the fabricated heterojunction. Moreover, cyclic interpretation and free radical capture research have confirmed both the high stability of catalyst and its Z-type charge transfer mechanism.

Signatures of cosmic ray heating in 21-cm observables

ABSTRACT Cosmic rays generated by supernovae carry away a significant portion of the lifetime energy emission of their parent star, making them a plausible mechanism for heating the early universe intergalactic medium (IGM). Following a review of the existing literature on cosmic ray heating, we develop a flexible model of this heating mechanism for use in 3D seminumerical 21-cm signal simulations and conduct the first investigations of the signatures it imprints on the 21-cm power spectrum and tomographic maps. We find that cosmic ray heating of the IGM is short-ranged, leading to heating clustered around star-forming sites, and a sharp contrast between heated regions of 21-cm emission and unheated regions of absorption. This contrast results in greater small-scale power for cosmic ray heated scenarios compared to what is found for X-ray heating, thus suggesting a way to test the nature of IGM heating with future 21-cm observations. Finally, we find an unexpectedly rich thermal history in models where cosmic rays can only escape efficiently from low-mass haloes, such as in scenarios where these energetic particles originate from population III star supernovae remnants. The interplay of heating and the Lyman–Werner feedback in these models can produce a local peak in the IGM kinetic temperature and, for a limited parameter range, a flattened absorption trough in the global 21-cm signal.