Positions Of Energy Levels Research Articles

The spectral investigations of interaction between high-molecular proteins and small adenine derivates

The spectral properties of co-systems of the DNA, RNA, and small nucleotide derivates with high-molecular π-electron-containing proteins were investigated. The positions of the first excited electronic energy levels of these compounds were verified. AT-complex in the DNA, adenine groups in the RNA/oligoadenylate, and tryptophane groups in the proteins were examined as the main triplet electronic excitations traps. The changes in fluorescence and phosphorescence spectra of the co-systems mentioned above under a variation of mutual concentrations of the oligoadenylate and protein macromolecules were observed. The spectral response of the binding of the oligoadenylate to the proteins (Human Albumin, Interferon, Immunoglobulin, Insulin) was fixed.

Evaluation of photocatalytic performances of PEG and PVP capped zinc sulfide nanoparticles towards organic environmental pollutant in presence of sunlight

Advanced oxidation processes triggered by nanoscale materials are promising owing to the in-situ generation of reactive radicals that can degrade toxic organic pollutants. In the present study, zinc sulfide (ZnS) nanoparticles with polyethylene glycol-4000 (PEG-4000) and polyvinylpyrrolidone (PVP) cappings were prepared using the chemical precipitation method and characterized thoroughly. Optical and structural characteristics of the capped ZnS nanoparticles were investigated and compared with those of uncapped ZnS nanoparticles. Results showed that PVP and PEG capped ZnS nanoparticles exhibited smaller crystallite size of 1.42 and 1.5 nm, respectively, as compared to uncapped ZnS (1.93 nm). Consequently, band gap energies of capped ZnS nanoparticles were higher which enable them to work as solar photocatalyst. The photocatalytic performance of the PEG, PVP-capped, and uncapped ZnS nanoparticles were evaluated against methyl orange (MO) dye and showed 85%, 87%, and 80% dye removal efficiencies, respectively. Degradation rate constant derived using Langmuir-Hinshelwood model revealed faster degradation kinetics bycapped ZnS photocatalysts owing to broader light absorption range. A possible dye degradation mechanism based on the energy levels positions was proposed to explain the route of photocatalytic degradation of MO by ZnS materials. It was inferred that the generation of reactive oxygen species by photogenerated electron-hole pairs facilitate degradation of MO dye molecules under sunlight illumination. It is expected that this work will provide insights into the development of strategies employed to achieve enhanced photocatalysis by nanoscale materials through organic capping.

Design, synthesis and mechanism of green afterglow phosphors Zn4B6O13:Mn2+ doped with Ln3+ (Ln = Sm, Yb, Eu) guided by VRBE

In this work, the construction of host referred binding energy (HRBE) diagram and vacuum referred binding energy (VRBE) diagram is described in detail. The energy gap of Zn4B6O13 is calculated by diffuse reflectance spectroscopy and the energy level positions of Eu3+ in VRBE are determined by the charge transfer (CT) band of Zn4B6O13 doped Eu3+ to construct a complete lanthanide ions VRBE diagram. According to the constructed VRBE of Zn4B6O13 system, novel long-afterglow phosphors Zn4B6O13:Mn2+ co-doped with Ln3+ (Ln = Sm, Yb, Eu) is designed and synthesized successfully. The influence of B2O3 contents on the crystal structure and luminescence of the Mn2+ doped zinc borate phosphors were analyzed by XRD and emission spectra. Photoluminescence excitation and emission spectra, persistent luminescence spectra and afterglow decay curve indicate that the doping of lanthanide ions Sm3+ and Yb3+ prolonged the afterglow duration of green emission of Mn2+ effectively. The fitting results of persistent luminescence spectra is consistent with the fast decay process of afterglow decay curve. The energy level depths of Sm3+ and Yb3+ traps obtained by thermoluminescence analysis are 0.49 eV and 1.12 eV respectively, which are in good agreement with the results calculated by VRBE. The energy level position of Sm3+ and Yb3+ below the conduction band (CB) are suitable trap depth, which can store and release electrons continuously. However, that of Eu3+ is too deep to enhance the afterglow. According to the VRBE theory, the mechanism of the electron trap is satisfactorily explained, which is important to the subsequent research of system design and mechanism explanation of lanthanide ions doped long afterglow materials.

Construction of WO3/CsPbBr3 S-scheme heterojunction via electrostatic Self-assembly for efficient and Long-Period photocatalytic CO2 reduction

Owing to the severe photogenerated carriers recombination and low oxidation ability, the photocatalytic performance of pristine CsPbBr3 is still unsatisfactory. Herein, melamine foam supported S-scheme WO3/CsPbBr3 heterojunction is successfully synthesized by electrostatic self-assembly. Because of the appropriate energy level positions, an S-scheme charge migration route between CsPbBr3 and WO3 is constructed. Under solar light irradiation, melamine foam assisted WO3/CsPbBr3 exhibits significantly enhanced photocatalytic CO2 reduction performance under liquid H2O medium, and the electron consumption rate (Relectron) reaches to 1225.50 μmol.g−1.h−1, which is 1.49- and 13.7-fold of CsPbBr3 and WO3, respectively, ascribing to the boosted charges transfer and the strengthened redox ability. Furthermore, S-scheme WO3/CsPbBr3 heterojunction also exhibits strong durability, with no noticeable reduction of product yields after four 8-h cycles.

High electrical transport performance of C12A7: e– ceramics electrides on Cu‐doping

Abstract(Ca1‐xCux) 12A7: e– bulks (0 ≤ x ≤ 0.05) with electrical performance were fabricated by the in‐situ aluminothermic synthesis. The results showed that all the electron concentrations of (Ca1‐xCux) 12A7: e– reached the theoretical value of about 2.28 × 1021 cm–3. In (Ca0.96Cu0.04) 12A7: e–, the electron mobility at room temperature increased from 3.81 to 5.19 cm2 V–1 S–1 and the conductivity increased from 415 to 1405 S cm–1. It indicated that Cu‐doping effectively improved electrical properties. The photoexcitation property also changed positively. The energy required for electrons to transition from cage conduction band to frame conduction band showed a decreasing trend, from 2.23 to 1.48 eV. The first‐principle calculation showed an upward shift in the Fermi energy level position of C12A7: e–. In addition, Cu atoms provided more density of states near the Fermi energy level. The number of empty orbitals near the Fermi surface of (Ca1‐xCux) 12A7: e– that can receive excited electrons increased. It provided a theoretical basis for preparing (Ca1‐xCux) 12A7: e– with high electrical transport characteristics.

Optimization of interfacial characteristics of antimony sulfide selenide solar cells with double electron transport layer structure

Antimony sulfide selenide thin film solar cells have drawn great interest in the field of photovoltaic due to their advantages of simple preparation method, abundant raw materials, non-toxic and stable photoelectric properties. After the development in recent years, the photoelectric conversion efficiency of antimony sulfide selenide solar cells has exceeded 10%, which has great development potential. In this work, the carrier recombination near n/i interface in antimony sulfide selenide solar cells is studied. It is found that the characteristics of the n/i interface are affected by the interfacial electron mobility and energy band structure. The improvement of the interface electron mobility can make the electrons more effectively transferred to the electron transport layer, and realize the effective improvement of the short circuit current density and fill factor of the device. Moreover, the introduction of ZnO/Zn<sub>1–<i>x</i></sub>Mg<sub><i>x</i></sub>O double electron transport layer structure can further optimize the performance of antimony sulfide selenide solar cells. The change of Zn<sub>1–<i>x</i></sub>Mg<sub><i>x</i></sub>O energy level position can adjust the energy level distribution of the interface and light absorption layer simultaneously. When the conduction band energy level of Zn<sub>1–<i>x</i></sub>Mg<sub><i>x</i></sub>O is –4.2 eV and the corresponding Mg content is 20%, the effect of restraining the carrier recombination is the most obvious, and the antimony sulfide selenide solar cell also obtains the best device performance. Finally, under the ideal condition of removing the defect state, the antimony sulfide selenide solar cells with 600 nm in thickness can achieve 20.77% theoretical photoelectric conversion efficiency. The research results provide theoretical and technical support for further optimizing and developing the antimony sulfide selenide solar cells.

Enhancing photovoltaic performance of carbon-based planar Cs3Sb2I9-xClx solar cells by using P3HT as hole transport material

The existence of toxic lead (Pb) remains a main handicap to the commercial application of perovskite solar cell (PSC). Although antimony (Sb)-based all-inorganic perovskite-like solar cells can overcome the toxicity and instability of hybrid Pb-based PSC, the Sb-based all-inorganic cell presents poor photoelectric conversion efficiency (PCE). Herein, we report a novel strategy that adopts poly (3-hexylthiophene) (P3HT) to modify the Cs3Sb2I9−xClx/carbon interface in carbon-based planar Cs3Sb2I9−xClx solar cells. It was found that the Cs3Sb2I9−xClx solar cell comprising P3HT exhibits less Voc deficit and higher PCE (1.67%). The mechanism behind performance improvement of P3HT-based Cs3Sb2I9−xClx device is suitable energy level position and high hole transport rate with low recombination. Moreover, the introduction of the P3HT layer has no negative impact on the stability of the carbon-based planar Cs3Sb2I9−xClx device.

Amino-functionalized NH2-MIL-125(Ti)-decorated hierarchical flowerlike Znln2S4 for boosted visible-light photocatalytic degradation

Developing novel heterojunction photocatalysts with visible-light response and remarkable photocatalytic activity have been verified to applying for the photodegradation of antibiotics in water environment. Herein, NH2-MIL-125(Ti) was integrated with flowerlike ZnIn2S4 to construct NH2-MIL-125(Ti)@ZnIn2S4 heterostructure using a one-pot solvothermal method. The photocatalytic performance was evaluated by the degradation of tetracycline (TC) under visible light illumination. The optimized NM(2%)@ZIS possesses a photodegradation rate (92.8%) and TOC removal efficiency (58.5%) superior to pristine components, which can be principally attributed to the positive cooperative effects of well-matched energy level positions, strong visible-light-harvesting capacity, and abundant coupling interfaces between the two. Moreover, the probable TC degradation mechanism was also clarified using the active species trapping experiments. This study inspires further design and construction of NH2-MIL-125(Ti) and ZnIn2S4 based photocatalysts for effective removal of antibiotics in water environment.

Electronics and coordination engineering of atomic cobalt trapped by oxygen-driven defects for efficient cathode in solar cells

A rational design and the metal coordination environment regulating of single-atom catalysts (SACs) in specific catalytic reaction remain great challenges. The oxygen defective support can be employed as traps to capture metal species, which provides an effective pathway to synthesize SACs. Here, we propose a counterions-assisted oxygen-driven defect capture (CODC) strategy to fabricate a series of atomically dispersed Co-based catalysts with different electronic and coordination environments. When serving as cathode for dye-sensitized solar cells (DSCs), the triiodine reduction reaction (IRR) activity is very sensitive to the coordination structure. Density functional theory (DFT) calculations reveal that the intrinsic electronic distributions, electron-donating ability, and energy level position determine the coordination behavior and catalytic performance of SACs. Our findings not only define an efficient synthetic strategy to a broad class of M-N x C y based SACs for highly-efficient IRR, but also provide an insight for exploring coordination-sensitive reaction from the atomic view. • An electronic and coordination environment control for accelerating the IRR process was developed. • The atomically dispersed Co-based catalysts were synthesized by a counterions-assisted oxygen-driven defect capture strategy. • The IRR catalytic activity was sensitive to the coordination structure of atomic cobalt. • The electron-donating ability and energy level position determined the coordination behavior of SACs by DFT study.

Activation energy distribution in thermal quenching of exciton and defect-related photoluminescence of InP/ZnS quantum dots

Thermal quenching is one of the essential factors in reducing the efficiency of radiative processes in luminophores of various nature. The emission activity of low-dimensional structures is influenced also by multiplicity of parameters that are related to synthesis processes, treatment regimes, etc. In the present work, we have investigated the temperature dependence of photoluminescence caused by exciton and defect-related transitions in ensembles of biocompatible InP/ZnS core/shell nanocrystals with an average size of 2.1 and 2.3 nm. The spread in the positions of energy levels is shown to be due to size distribution of quantum dots in the ensembles under study. For a quantitative analysis of the experimental data, we have proposed a band model accounting for the Gaussian distribution of the thermally activated barriers in the photoluminescence quenching processes. The model offers the thermal escape of an electrons from the core into the shell as the main mechanism for non-radiative decay of excitons. In turn, the quenching of defect-related emission is predominantly brought about through the emptying of the hole capture centers based on dangling phosphorus bonds. We have revealed the correlation between size distributions of quantum dots and scatter of the activation energy of exciton luminescence quenching. The developed approach will give further the possibility to optimize technological regimes and methods for band engineering of indium phosphide-based type-I quantum dots.

Structural diversity in four coordination polymers based on polypyridyl ligand regulated by metal centers for photodegradation of methylene blue and methyl orange

Four coordination polymers (CPs) based on π-conjugated polypyridyl ligand {[Cu(HL) (5-Me-IPA)]·0.25H2O}n (1), {[Co(HL) (5-Me-IPA)]·0.25H2O}n (2), {[Zn(HL) (5-Me-IPA)]}n (3) and {[Zn(HL) (5-Me-IPA)]·H2O}n (4) (HL ​= ​4'-(4-hydroxyphenyl)-4,2':6′,4″-terpyridine, 5-Me-IPA ​= ​5-methyl-iso-Phthalic acid) have been solvothermally synthesized by controlling metal centers and pH condition, exhibiting three-dimensional framework with Schläfli symbol of 66 (for 1) and 658 (for 2) and two-dimensional network for 3 and 4. The photodegradation of methylene blue (MB) and methyl orange (MO) over 1–4 have been investigated, indicating complex 1 exhibits the best photocatalytic activity with degradation rates of 83.9% (for MB in 150 ​min) and 70.7% (for MO in 300 ​min) resulting from the band gap, position of valence band energy levels, separation of electrons and holes, and charge carrier mobility regulated by copper center. This work provides an example of structure-function relationship for photodegradation of organic dyes over coordination polymers.

A Brief Study on Optical and Mechanical Properties of an Organic Material: Urea Glutaric Acid (2/1)—A Third Order Nonlinear Optical Single Crystal

Urea glutaric acid (UGA), an organic crystal, was synthesized and grown using a low temperature solution technique. Single crystal XRD revealed a monoclinic structure with a C2/C space group. The various cell data were identified. The optical parameters were calculated from UV-visible spectrum. The transmittance spectra showed the cutoff wavelength as 240 nm (low) and the energy gap determined from the spectra was compared with the theoretical energy gap. The transition number revealed the electron transition, which corresponded to direct allowed transition. The diverse optical parameters like reflectance, extinction coefficient, refractive index and optical susceptibility were determined. The least value of Urbach energy caused less defects and a good crystalline nature. The steepness value and electron phonon interaction were calculated. The positions of lower and higher band energy levels were identified. Electronic polarizability was found using the Clausius–Mossoti relation and tabulated. The mechanical fitness was measured from Vickers hardness analysis. The nonlinear optical property was measured from Z-scan analysis. Thus, the optical results support the material suitability and fitness for optical and electronic domain applications.

Solar light-driven 2D MoS2 nanoflake-supported 1D ZnWO4 nanorod heterostructure: Efficient separation of charge carriers for removing toxic organic pollutants

In this study, a novel photocatalyst for efficiently eliminating toxic and harmful antibiotics from water bodies was prepared successfully. Precisely, MoS2/ZnWO4 (MSZW) heterostructures were prepared using a facile hydrothermal technique. The constructed samples were characterized by using structural, morphological, diffuse reflectance spectroscopy, and photoluminescence measurements. The efficiencies of the catalysts were investigated using the removal of tetracycline (TC) antibiotic under stimulated solar light irradiation. Among the prepared photocatalysts, the optimal MSZW-10 heterostructure displayed superior photocatalytic performance and degrade ~97.40% of TC within 105 min. Moreover, the photocatalytic performance of MSZW-10 is approximately ~6.18 and ~10.77 times greater over pure MoS2 and ZnWO4, respectively. The progress in the photocatalytic performance chiefly owing to its improved partition of charge carriers, the robust positive synergistic effect of suitable positions of energy levels, improved light absorption ability, and enhanced interfacial charge transfer between MoS2 and ZnWO4. The MoS2/ZnWO4 composite exhibits significantly enhanced photocatalytic performance as well as excellent reusability performance, thus indicating its applicability in wastewater treatment.

Charge Density Based Small Signal Modeling for InSb/AlInSb Asymmetric Double Gate Silicon Substrate HEMT for High Frequency Applications

This paper proposes the Asymmetric Double Gate Silicon Substrate HEMT (ADG-Si-HEMT) to study the carrier concentration and intrinsic small signal parameters of the InSb/AlInSb silicon wafer DG-HEMT device. The HEMTs work as a three-port system and the device is named Asymmetric Double Gate HEMT when the top and bottom gates are biased with different gate voltages. The position of quasi-Fermi energy levels (Ef) is used to investigate the modulation of back-channel charge density caused by the front gate voltage. Also, the small signal model is obtained for a various parameters such as cut off frequency, gate to source capacitance and transconductance. To enhance device operation, the effects of the following factors are being investigated delta doping, drain current for various top and bottom gate voltages. The transconductance 2390 Sm/mm for Vfg = 0.2 V and cut off frequency around 197 GHz for Vbg = 0.3 are obtained. The analytical results are compared to the results of the Sentaurus 3-D TCAD simulation. Because of the variation in threshold voltage and modifying carrier density in dual channels, the asymmetric biassing approach has a wide range of mixed applications.

MoO3/g-C3N4 heterostructure for degradation of organic pollutants under visible light irradiation: High efficiency, general degradation and Z-scheme degradation mechanism

The development of semiconductor photocatalyst with simple and controllable components, high catalytic efficiency and cycle stability, and diversified degradation goals is an important condition for achieving large-scale commercial applications for environmental remediation. The achievement of these important performance indicators requires the precise modulation of the components and the clarification of the photocatalysis process and charge transfer mechanisms. In this work, we have fabricated a heterostructured photocatalyst composed of graphite carbon nitride (g-C3N4) nanosheets and MoO3 nanoparticles through a simple mixing and annealing process. The compound exhibits effective visible light photocatalytic activity for both rhodamine (RhB) and methyl orange (MO). In the evaluation of RhB catalytic performance, the optimized heterojunction photocatalyst achieves extremely high visible light photocatalytic performance with a small amount of catalyst (0.1 g/L). It is characterized by nearly 100% degradation rate within 24 min. The kinetic constant k is 0.11 min−1, and the cycle stability is 100% after four cycles. Direct Z-scheme charge transfer is established based on the measurement of energy level positions, free radical scavenging experiment and electrochemical analysis. Electrons accumulate in the g-C3N4 conduction band while holes remain in the MoO3 valence band, maintaining a high redox potential and promoting effective carrier separation. Superoxide radicals and holes play a prominent role in photocatalytic degradation, and the role of hydroxyl radicals cannot be ignored.

Ultrafast electrical control of optical polarization in hybrid semiconductor structure

We theoretically analyze the dynamics of circular polarized photoluminescence (PL) associated with split-off states emerging in a semiconductor quantum well (QW) due to tunnel coupling with remote spin-split bound states. A mechanism for ultrafast PL polarization switching is proposed based on tunnel barrier transparency modulation. Such modulation can be experimentally realized by applying a gate voltage to the semiconductor heterostructure. The proposed mechanism is based on the split-off state energy level position being sensitive to the transparency of the tunnel barrier. The obtained results open the possibility to form fully polarized PL signal and are promising for applications in spintronics, in particular, for ultrafast polarization modulation in spin lasers. • A mechanism for ultrafast PL polarization switching is proposed in a hybrid structure. • The role of the split-off states in the PL polarization switching is revealed. • Position of the split-off states is very sensitive to the tunnel coupling between the QW and the bound state. • The obtained results open the possibility to effective and fast control of PL polarization.

The stabilization of Ni(OH)2 by In2O3 rods and the electrochromic performance of Ni(OH)2/In2O3-rod composite porous film

In this paper, a Ni(OH)2/In2O3-rod composite film with a porous structure was prepared by hydrothermal and solvothermal techniques using fluorine-doped tin oxide conductive glass as a substrate to improve the film/substrate connection and the cycle stability of the Ni(OH)2 film. A blank Ni(OH)2 film was also prepared for comparison purposes. The morphology, microstructure, and components of the films were characterized through X-ray photoelectron spectroscope, scanning electron microscope, and X-ray diffractometer. The electrochromic performance of the films including transmittance, cyclic voltammetry, cycle stability, electrochemical impedance, and switch speed was examined. The energy level positions and band gaps of the fluorine-doped tin oxide conductive glass and In2O3 layers were calculated based on their Mott–Schottky plots and ultraviolet-visible diffuse reflectance spectra. The results show that the In2O3 rods are approximately perpendicular to the substrate. The introduction of the In2O3 rod array transition layer enhanced the film/substrate connection in addition to providing favorable conditions for the nucleation and growth of Ni(OH)2, resulting in the improved Ni(OH)2 stability and porous structure as well as electrochromic performance. The mechanism of the improvement is explained in this paper.

Energy Level Locations of Lanthanide Ions in Strontium-Aluminosilicate Phosphors

This paper determines the position of energy levels of lanthanide ions in Sr2Al2SiO7 (SAS) phosphor by a combining analysis of the lowest 4f-5d transition of Ce3+ ions and the charge transfer of Eu3+ ions-doped SAS phosphor. The SAS samples were successfully synthesized via solid state reaction, and their structure phase was further confirmed by X-ray diffraction. In the case of Eu3+-doped SAS phosphors, the energy of the charge transfer (CT) transition of the Eu3+ is about 4.70 eV (264 nm) and this energy is applied to determine the position 4f level of all divalent lanthanides relating to the top of the valence band in the SAS host lattice. For Ce3+ activated SAS samples, the lowest 4f1→4f05d1 excitation energy is determined around 3.71 eV (334 nm) and it is used to estimate the lowest 4f-5d transitions for all lanthanide (Ln) ions in host lattice. A broad band emission of the 5d→4f transition of Ce3+ ions includes two peaks emission with different energy about 1997 cm-1 that coincides with the theoretical value of 2000 cm-1. The host referred binding energy (HRBE) diagram of all Ln2+ and Ln3+ ions relating to the valance band of SAS materials has been constructed by using the data of fluorescent properties of Ce3+ and Eu3+ ions. The energy of 4f→5d transitions of Eu2+ ions that was predicted from the energy level scheme matches well with the observed experimental energy.

The Impact of UV Photoelectron Spectroscopy on the Field of Organic Optoelectronics—A Retrospective

AbstractThe field of organic electronics has been of widespread interest for a long time. Over the years, device efficiencies increased steadily due to the development of new materials, as well as an improved understanding of the physical mechanisms governing underlying fundamental processes such as charge transport or charge carrier generation and recombination. Especially the positions of energy levels that are responsible for the charge transport throughout a device are of paramount importance. This generated a high demand for reliably measured values. The most important technique that can directly access these values in a thin film is photoelectron spectroscopy. The very fruitful collaboration between surface scientists and device specialists is ​ reviewed here, showing a range of experiments through which UV photoelectron spectroscopy helped to unravel the working mechanisms of organic semiconductors in devices.

Substrate temperature dependence of material, optical, and electronic properties of boron-doped ZnO thin films

Abstract Sputtered boron-doped ZnO (BZO) thin films at deposition temperature ranging from 300 °C to 600 °C are studied in this work. The BZO films exhibit preferred orientation of (002) planes. The surface morphology is dependent on deposition temperature, characterized essentially by three distinct features. Hall-effect measurements suggest that the BZO film deposited at 400 °C show the optimum results of carrier concentration, mobility, and resistivity with values that can reach 2.06 × 10 20 cm−3, 5.38 cm2/ V ⋅ s , and 5.64 × 10 − 3 Ω ⋅ cm , respectively. By combining the optical band gap from transmittance spectra and work function from ultraviolet photoemission spectroscopy, the band structure of BZO films is derived. The positions of BZO energy levels presented in this study can provide insights into band engineering in BZO-based optoelectronic devices.