Electronic Energy Level Structure Research Articles

Rare earth oxide based electrocatalysts: synthesis, properties and applications.

As an important strategic resource, rare earths (REs) constitute 17 elements in the periodic table, namely 15 lanthanides (Ln) (La-Lu, atomic numbers from 57 to 71), scandium (Sc, atomic number 21) and yttrium (Y, atomic number 39). In the field of catalysis, the localization and incomplete filling of 4f electrons endow REs with unique physical and chemical properties, including rich electronic energy level structures, variable coordination numbers, etc., making them have great potential in electrocatalysis. Among various RE catalytic materials, rare earth oxide (REO)-based electrocatalysts exhibit excellent performances in electrocatalytic reactions due to their simple preparation process and strong structural variability. At the same time, the electronic orbital structure of REs exhibits excellent electron transfer ability, which can reduce the band gap and energy barrier values of rate-determining steps, further accelerating the electron transfer in the electrocatalytic reaction process; however, there is a lack of systematic review of recent advances in REO-based electrocatalysis. This review systematically summarizes the synthesis, properties and applications of REO-based nanocatalysts and discusses their applications in electrocatalysis in detail. It includes the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), methanol oxidation reaction (MOR), nitrogen reduction reaction (NRR) and other electrocatalytic reactions and further discusses the catalytic mechanism of REs in the above reactions. This review provides a timely and comprehensive summary of the current progress in the application of RE-based nanomaterials in electrocatalytic reactions and provides reasonable prospects for future electrocatalytic applications of REO-based materials.

All-optical modulation by continuous wave light using two-color excited-state absorption at visible wavelengths.

We demonstrated all-optical modulation with a nonlinear medium, i.e., indigo carmine, an aromatic conjugated structure with delocalized π-electrons, using non-high power continuous wave light for pump and probe of different visible wavelengths. Pump-induced probe transmission increase occurred through absorption saturation of probe light by pump-induced linear and nonlinear absorption including two-color excited-state absorption (ESA). The two-color ESA occurred only when both pump light and probe light co-propagated through a medium, leading to nearly pump power-independent increase in probe transmission for appropriately chosen wavelengths of pump and probe light, given the optical transition structure of electronic energy levels in the medium.

Quantum Junction Solar Cells: Development and Prospects

AbstractNanocrystals, called semiconductor quantum dots (QDs), contain excitons that are three‐dimensionally bound. QDs exhibit a discontinuous electronic energy level structure that is similar to that of atoms and exhibit a distinct quantum confinement effect. As a result, QDs have unique electrical, optical, and physical characteristics that can be used in a variety of optoelectronic device applications, including solar cells. In this review article, the stable and controllable synthesis of QD materials is outlined for upscaling solar cells, including material development and device performance enhancement. It includes a systematic variety of device structures for the fabrication of solar cells, such as QD, hybrid QD/organic, hybrid QD/inorganic, perovskite QD, and hybrid 2D MXene QD/perovskite. The mechanisms for the improvement of stability by QD treatment are examined. For example, the 2D MXene QD and/or Cu1.8S nanocrystal doping significantly increases the long‐term light and ambient stability of perovskite solar cells, resulting from improved perovskite crystallization, reduced hole transport layer (HTL) aggregation and crystallization of films, and reduced UV‐induced photocatalytic activity of the electron transport layer (ETL). For the advancement of QD solar cells and their interaction with various materials, the conclusions from this review are crucial. Finally, future prospects for the development of QD solar cells as well as current challenges are discussed.

Exploring electronic energy level structure and excited electronic states of β-carotene using DFT.

Carotenoids are a class of natural pigments that play a fundamental role in photosynthesis and optoelectronics. However, the complexity of their energy level structure and electronic states has prevented a clear interpretation of their photophysics and photochemistry. The mediating nonradiative decay of the bright S2 state to the dark S1 state of carotenoids involves a population of bridging intermediate state. Herein, time-dependent DFT was used to study the energy level and electronic excitation process of β-carotene. A π-π* transition and π electron delocalization of electron excitation could be inferred based on the difference in the electron cloud distribution of the HOMO and LUMO orbitals. Through the electronic transition contribution in the UV-vis spectra and the electron density difference between the ground state and the excited state, the electronic energy level structure and possible dark state were analyzed. On this basis, the electronic excitation process of β-carotene was theoretically studied by combining electron-hole analysis and transition density matrix (TDM). There was a charge transfer from the β-ionone ring to the long-chain in the (S0) → (S2), (S0) → (S4) and (S0) → (S5).

In-situ oriented Sc-Co3O4 nanowire arrays for highly efficient ethanol detection

Improving the response of gas sensors has always been a hot research topic. Due to their unique electronic energy level structure, the compositing rare-earth (RE) element materials display unique properties in many fields such as catalysis, luminescence, and energy conversion. Along these lines, combining materials with the RE element of scandium (Sc) is considered a new method to optimize the performance of sensors based on the employment of ZIF-67 derived Co3O4 nanowire arrays. In this work, the Sc element was uniformly distributed on the surface of the Co3O4 nanowires, which were grown by enforcing hydrothermal and chemical bath-based methods. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors show a maximum response of 32–100 ppm ethanol at a lower operating temperature (110 °C). The variation of the response was small range even after 35 days. Interestingly, the extracted response has increased more than three times that of the pure Co3O4 nanowire array devices. In addition, we tested the ethanol concentration range of 10–500 ppm and showed good performance. The gas-sensing properties of the sensors were systematically tested towards volatile organic compounds, including ethanol, acetone, methanol, etc. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors still exhibit excellent selectivity to ethanol. The enhanced sensing performance is attributed to the strong catalytic effect of Sc and the modification of the surface morphology of Co3O4 by Sc. Our work provides an effective and promising method for improving the ethanol sensing performance of the ZIF-67 derived Co3O4 nanowires at low-temperature values.

Efficient photocatalytic hydrogen evolution over Cu3Mo2O9/TiO2 p-n heterojunction

The heterojunction formed by semiconductors with a matching electronic energy level structure can effectively promote charge transfer, thereby greatly improving the photocatalytic hydrogen production activity of the catalyst. Herein, the Cu3Mo2O9/TiO2 hybrid was prepared via a simple mechanical mixing method. In the binary composite, the p-n heterojunction formed between Cu3Mo2O9 and TiO2 can favor the charge separation, resulting in excellent hydrogen production rate of 3401.9 μmol·g−1·h−1, it is 14.5-fold of pristine TiO2. According to the optional and photoelectrochemical properties, it can be confirmed that Cu3Mo2O9 plays a pivotal role in accelerating charge transfer and improving light absorption capacity of the composite. As a new type of photocatalyst, there is very limited information on Cu3Mo2O9 for its application in photocatalytic hydrogen production. This work provides the possibility to expand application range of Cu3Mo2O9 in energy conversion.

Near‐Infrared Photoactive Semiconductor Quantum Dots for Solar Cells

AbstractSemiconductor quantum dots (QDs) are nanocrystals whose excitons are bound in 3D space. Owning to their remarkable quantum confinement effect, QDs exhibit a discontinuous electronic energy level structure similar to that of atoms, leading to novel physical, optical, and electrical properties for various optoelectronic device applications including solar cells. Near‐infrared photoactive narrow bandgap (NBG) QDs can maximize the use of solar energy through the quantum size effect, offering a good opportunity for designing highly efficient wide‐spectrum responsive solar cells. This review analyzes the recent research progress of NBG QDs as light absorbing materials in solar cells. The critical elaboration of the latest achievements both in material design and device optimization for NBG QD‐based solar cells (QDSCs), including QD synthesis and film fabrication, design of device configuration, classification of NBG QDs and their photovoltaic performance, strategies for performance improvements is focused upon. The current challenges and perspectives for the further advance of NBG QDSCs are also discussed.

Integrating biphase γ- and α-Fe2O3 with carbon dots as a synergistic nanozyme with easy recycle and high catalytic activity

A new method is offered for the synthesis of heteronanostructures as a multifunctional catalyst mimicking functions of dual- or multi-enzyme activities. In this method, the coordination reaction and surface adsorption are firstly used to preform ferrous and ferric ion-modified carbon dots (CDs) for regulating heterogeneous nucleation process of iron oxide. Thus a unique multiphase nanostructure containing CDs and biphase γ- and α-Fe2O3 is obtained under hydrothermal conditions. As-prepared heteronanostructure with magnetic properties shows excellent enzyme-like activities under visible light irradiation, which is more than a 6-fold enhancement compared to pure phase Fe2O3 nanomaterials. This could be attributed to highly efficient charge separation and transfer efficiency induced by heterogeneous interfaces as well as multiphase-induced new electronic energy level structure. Moreover, its catalytic activities can be also tuned by temperature, pH, hydrogen peroxide and levels of oxygenation in microenvironments. Not only does this work open an effective strategy to design novel heteronanostructures, but it also may provide a synergistic nanozyme as a multimodal platform for a broad of applications.

Realizing the Control of Electronic Energy Level Structure and Gas-Sensing Selectivity over Heteroatom-Doped In2O3 Spheres with an Inverse Opal Microstructure.

Understanding the effect of substitutional doping on gas-sensing performances is essential for designing high-activity sensing nanomaterials. Herein, formaldehyde sensors based on gallium-doped In2O3 inverse opal (IO-(Ga xIn1- x)2O3) microspheres were purposefully prepared by a simple ultrasonic spray pyrolysis method combined with self-assembled sulfonated polystyrene sphere templates. The well-aligned inverse opal structure, with three different-sized pores, plays the dual role of accelerating the diffusion of gas molecules and providing more active sites. The Ga substitutional doping can alter the electronic energy level structure of (Ga xIn1- x)2O3, leading to the elevation of the Fermi level and the modulation of the band gap close to a suitable value (3.90 eV), hence, effectively optimizing the oxidative catalytic activity for preferential CH2O oxidation and increasing the amount of adsorbed oxygen. More importantly, the gas selectivity could be controlled by varying the energy level of adsorbed oxygen. Accordingly, the IO-(Ga0.2In0.8)2O3 microsphere sensor showed a high response toward formaldehyde with fast response and recovery speeds, and ultralow detection limit (50 ppb). Our findings finally offer implications for designing Fermi level-tailorable semiconductor nanomaterials for the control of selectivity and monitoring indoor air pollutants.

Carbon nitride nested tubes with graphene as a dual electron mediator in Z-scheme photocatalytic deoxynivalenol degradation

Schematic illustration of the electronic energy level structure and mechanism in the photocatalytic reaction of Z-scheme CNTZG systems under light irradiation.

Modeling of luminescence-based oxygen sensing by redox-switched energy transfer in nanocrystalline TiO2:Sm3+

It is shown that the luminescence of Sm3+ ions, which were doped into anatase nanopowder, is highly sensitive to the presence of oxygen gas. The luminescence was effectively excited through TiO2 band-to-band absorption and exhibited oxygen sensitivity in a wide concentration range from pure O2 gas down to 100 ppm of O2 in a nitrogen atmosphere. An increase in oxygen concentration led to a stronger intensity and longer lifetime of Sm3+ luminescence, an exactly opposite behavior to luminescence-based sensors described by Stern-Volmer law. An original physical model is developed for describing such luminescent enhancement mechanism: it is proposed, that the adsorbed oxygen suppresses the inherent luminescence quenching of Sm ions taking place via a resonant energy transfer to acceptor defects in the material. Electron transfer between the adsorbed oxygen and these defects changes the structure of electronic energy levels and hence the energy accepting ability of the latter. The model allows describing the oxygen-dependent non-exponential luminescence decays in a quantitative manner and relates the luminescence characteristics to the material parameters such as the surface-to-volume ratio of nanocrystallites and the density of acceptor defects and gas adsorption sites.

Low-temperature rapid synthesis of nitrogen and phosphorus dual-doped carbon dots for multicolor cellular imaging and hemoglobin probing in human blood

Heteroatom doping of carbon dots (CDs) can efficiently tune the structure of electronic energy levels and modulate the photochemical properties of CDs. However, the reported synthesis routes of heteroatom-doped CDs are complicated and rigorous. Herein, a simple and rapid low-temperature heating strategy was applied to synthesize fluorescent nitrogen and phosphorus dual-doped CDs (N,P-CDs) using sucrose as carbon source, and 1,2-ethylenediamine (EDA) and phosphoric acid as dopants, respectively. These N,P-CDs exhibit excellent fluorescent stability over wide pH range solutions (4–11), ultrahigh ion strength (3 M KCl), and longtime UV light irradiation (3 h continuously), which makes these N,P-QDs promising good candidates for fluorescent probes. These N,P-CDs showed excellent biocompatibility, multicolor cellular imaging, and non-cytotoxicity to human hepatocellular carcinoma HepG2 cells even at 500 μg/mL levels for 48 h incubation. These N,P-CDs exhibited a strong blue emission and a sensitive response to hemoglobin. The N,P-CDs based fluorescent probe was then applied to sensitively determine hemoglobin with a detection limit of 0.29 nM. Notably, it was also applied for label-free detection of hemoglobin in human urine samples and human blood samples, which indicated its potential applications in clinical diagnosis and other biologically related study.

A solid reaction towards in situ hybridization of carbon dots and conjugated polymers for enhanced light absorption and conversion.

We for the first time developed a green and very simple method towards carbon-dot-incorporated poly(diphenylbutadiyne) nanohybrids (PDPB) through a solid reaction without the need of a template, a solvent and a surfactant. The incorporation of carbon dots into the PDPB nanostructures not only significantly improved visible light absorption but also enhanced photocatalytic performances.

New insights into the temperature-dependent photoluminescence of Mg-doped GaAs nanowires and epilayers

The intentional introduction of impurities in semiconductor nanowires is very important in view of device applications. Doping affects the electronic energy level structure which in the case of III–V nanowires can also be strongly influenced by the simultaneous occurrence of two polytypes, zinc-blende (ZB) and wurtzite (WZ). In this work, we report a study on GaAs nanowires with different Mg-acceptor doping levels through temperature dependent photoluminescence. A comparable investigation is presented for Mg-doped GaAs epilayers. For the later, only a band is observed which is ascribed to the involvement of the Mg acceptor due to the observed bandgap energy narrowing effect with increasing the doping level, and the temperature dependent behaviour. A different behaviour is reported for nanowires: several radiative transitions are observed whose temperature dependence follows that of bulk GaAs, in accordance with spatially indirect recombination. Although the polytypic regions mask the role of doping in nanowires it favours the charge separation required for photovoltaic applications.

Parameter free calculation of the subgap density of states in poly(3-hexylthiophene).

We investigate the influence of intra-chain and inter-chain interactions on the sub-gap density of states in a conjugated polymer using a combination of atomistic molecular dynamics simulation of polymer film structure and tight-binding calculation of electronic energy levels. For disordered assemblies of poly-3-hexylthiophene we find that the tail of the density of hole states is approximately exponential with a characteristic energy of 37 meV, which is similar to experimental values. This tail of states arises mainly from variations in the electronic coupling between neighbouring monomers, and is only slightly influenced by interchain coupling. Thus, knowledge of the disorder in torsion between neighbouring monomers is sufficient to estimate the density of states for the polymer. However, the intrachain torsional disorder is determined largely by the packing of the chains rather than the torsional potential alone. We propose the combination of methods as a tool to design higher mobility conjugated polymers.

Correction to “Analysis of Electronic States and Energy Level Structure of Uranyl in Compounds”

Correction to “Analysis of Electronic States and Energy Level Structure of Uranyl in Compounds”

Resonant coherent excitation of hydrogen-like ions planar channeled in a crystal; Transition into the first excited state

The presented program is designed to simulate the characteristics of resonant coherent excitation of hydrogen-like ions planar-channeled in a crystal. The program realizes the numerical algorithm to solve the Schrödinger equation for the ion-bound electron at a special resonance excitation condition. The calculated wave function of the bound electron defines probabilities for the ion to be in the either ground or first excited state, or to be ionized. Finally, in the outgoing beam the fractions of ions in the ground state, in the first excited state, and ionized by collisions with target electrons, are defined. The program code is written on C++ and is designed for multiprocessing systems (clusters). The output data are presented in the table. Program summary Program title: RCE_H-like_1 Catalogue identifier: AEKX_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEKX_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 2813 No. of bytes in distributed program, including test data, etc.: 34 667 Distribution format: tar.gz Programming language: C++ (g++, icc compilers) Computer: Multiprocessor systems (clusters) Operating system: Any OS based on LINUX; program was tested under Novell SLES 10 Has the code been vectorized or parallelized?: Yes. Contains MPI directives RAM: <1 MB per processor Classification: 2.1, 2.6, 7.10 External routines: MPI library for GNU C++, Intel C++ compilers Nature of problem: When relativistic hydrogen-like ion moves in the crystal in the planar channeling regime, in the ion rest frame the time-periodic electric field acts on the bound electron. If the frequency of this field matches the transition frequency between electronic energy levels, the resonant coherent excitation can take place. Therefore, ions in the different states may be observed in the outgoing beam behind the crystal. To get the probabilities for the ion to be in the ground state or in the first excited state, or to be ionized, the Schrödinger equation is solved for the electron of ion. The numerical solving of the Schrödinger equation is carried out taking into account the fine structure of electronic energy levels, the Stark effect due to the influence of the crystal electric field on electronic energy levels and the ionization of ion due to the collisions with crystal electrons. Solution method: The wave function of the electron of ion is the superposition of the wave functions of stationary states with time-dependent coefficients. These stationary wave functions and corresponding energies are defined from the stationary Schrödinger equation. The equation is reduced to the problem of the eigen values and vectors of Hermitian matrix. The corresponding matrix equation is considered as the linear equation system. Then the time-dependent coefficients of the electron wave function are defined from the Schrödinger equation, with a time-periodic crystal field. The time-periodic field is responsible for the transitions between the stationary states. The final time-dependent Schrödinger equation represents the matrix equation which has been solved by means of the QR-algorithm. Restrictions: As expected the program gives the correct results for relativistic hydrogen-like ions with the kinetic energies up to 1 GeV/u and at the crystal thicknesses of 1–100 μm. The restrictions are: first, the program might give inadequate results, when the ion kinetic energy is too large (>10 GeV/u); second, the unaccounted physical factors may be significant at specific conditions. For example, the spontaneous emission by exited highly charged ions, as well as both energy and angular spread of the incident beam, could lead to additional broadening of the resonance. The medium polarization by the electric field of ion can influence the electronic energy levels of the ion in the non-relativistic case. The role of these factors was discussed in the references. Also, the large crystal thickness may require large computational time. Running time: In general, the running time depends on the number of processors. In our tests we used the crystal thickness up to 100 μm and the number of 2.66 GHz processors was up to 100. The running time was about 1 hour in these conditions.

Analysis of Electronic States and Energy Level Structure of Uranyl in Compounds

An effective operator Hamiltonian has been developed for evaluating the excited states of uranyl ion in compounds. Including free-ion and crystal-field interactions, the parametrized Hamiltonian is able to reproduce the energy level structure in good agreement with experimental measurements on uranyl in chloride compounds and nitride complexes. It is shown that the low-lying excited states belong to a nonbonding σf configuration (therefore, one Slater integral of G(3) is sufficient to account for the Coulomb electron exchange interaction) and that the spin-orbit coupling surpasses the electrostatic interactions in energy level splitting. In comparison with previously reported ab initio calculations, the present studies find that the Coulomb interactions in uranyl were excessively evaluated in the first-principle calculations.

Self-assembled light lanthanide oxalate architecture with controlled morphology, characterization, growing mechanism and optical property

Flower-like Sm 2(C 2O 4) 3·10H 2O had been synthesized by a facile complex agent assisted precipitation method. The flower-like Sm 2(C 2O 4) 3·10H 2O was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, thermogravimetry–differential thermal analysis and photoluminescence. The possible growth mechanism of the flower-like Sm 2(C 2O 4) 3·10H 2O was proposed. To extend this method, other Ln 2(C 2O 4) 3· nH 2O (Ln = Gd, Dy, Lu, Y) with different morphologies also had been prepared by adjusting different rare earth precursors. Further studies revealed that besides the reaction conditions and the additive amount of complex agents, the morphologies of the as-synthesised lanthanide oxalates were also determined by the rare earth ions. The Sm 2(C 2O 4) 3·10H 2O and Sm 2O 3 samples exhibited different photoluminescence spectra, which was relevant to Sm 3+ energy level structure of 4f electrons. The method may be applied in the synthesis of other lanthanide compounds, and the work could explore the potential optical materials.

Two-dimensional C/BN core/shell structures

Single layer core/shell structures consisting of graphene as core and hexagonal boron nitride as shell are studied using first-principles plane wave method within density functional theory. Electronic energy level structure is analysed as a function of the size of both core and shell. It is found that the confinement of electrons in two dimensional graphene quantum dot is reduced by the presence of boron nitride shell. The energy gap is determined by the graphene states. Comparison of round, hexagonal, rectangular and triangular core/shell structures reveals that their electronic and magnetic states are strongly affected by their geometrical shapes. The energy level structure, energy gap and magnetic states can be modified by external charging. The core part acts as a two-dimensional quantum dot for both electrons and holes. The capacity of extra electron intake of these quantum dots is shown to be limited by the Coulomb blockade in two-dimension.