Electronic Energy Levels Research Articles

The optical phonon drag effect on strong-coupling decay magnetopolaron in Gaussian alkali halogen ionic quantum wells

The polaron phenomenon is commonly observed in low-dimensional semiconductor materials and is known to have unique effects on conductive material properties. Furthermore, the phonon dragging effect, which leads to the polaron energy level, is less than the electron energy level. A decay magnetic field also affects the polaron effect, which causes polaron energy level changes. We demonstrate the unique electron–phonon coupling properties of this polaron using numerical calculations. Our findings have strong implications for theories of polaron properties and provide compelling evidence for a semiconductor device that industrial manufacturers use for new low-dimensional materials.

Luminescence performance of Eu3+ doped 25La2O3-60Al2O3-15ZrO2 glass prepared by containerless method

Rare-earth metal Eu doped glass 25La2O3-60Al2O3-15ZrO2:xEu3+ (x = 0.1 wt%, 0.5 wt%, 1.0 wt%, 3.0 wt% and 5.0 wt%) was prepared by gas suspension containerless laser melting technology, which is transparent and has sphere ball shape. The glass shows excellent thermal stability although the temperature difference ΔT between crystallization initiation temperature To and glass transition temperature Tg (ΔT=To-Tg) is just between 48.6 ℃− 64.9 ℃, showing low glass forming ability and being difficult to prepare glass by traditional melt-quenching method. The Eu-doped glass preserves rather high transparency, and presents enhanced mechanical performance due to the Eu3+ doping, which improves glass network connectivity. Strong orange emission peak centered at 605 nm and red emission peak at 696 nm, and weak yellow emission peak centered at 582 nm and red emission peak at 646 are engendered under the excitation of 394 nm light, attributing to the 5D0→7F2, 5D0→7F4, 5D0→7F1, and 5D0→7F3 electron energy level transitions of Eu, respectively. The 25La2O3-60Al2O3-15ZrO2:xEu3+ phosphor glass has strong nearly standard red light with high color purity, which presents excellent candidate for red luminescent phosphor and shows potential application in white-light-emitting diode.

Persistent currents and electronic properties of Mandelbrot quantum rings

In this study, we investigate the persistent current, and electronic energy levels of Mandelbrot quantum rings. For this purpose, three types of Mandelbrot quantum rings are proposed. Furthermore, Mandelbrot equation is generalized by introducing parameter m, which makes Mandelbrot’s shape more symmetric by adding new branches to it, on the other hand, the iteration parameter M, controls geometrical deficiencies. We explain the procedure needed to form these structures, including a padding scheme, then we solve the resulting two-dimensional Schrodinger equation using the central finite difference method with uniform distribution of the mesh points. Thereafter, we obtain the persistent current in different situations including different Mandelbrot orders and quantum ring shapes. We show that the persistent current can have different shapes and intensities by changing the described geometrical parameters of Mandelbrot quantum rings. We explain this phenomenon by considering symmetries in the potential, and consequently the wavefunction.

Morphology, Energy Level Alignment, and Charge Transfer at the Protoporphyrin IX-Semiconductor Interface.

The combination of molecular catalysts and semiconductor substrates in hybrid heterogeneous photo- or electrocatalytic devices could yield synergistic effects that result in enhanced activity and long-term stability. The extent of synergy strongly depends on the electronic interactions and energy level alignment between the molecular states and the valence and conduction band of the substrate. These properties of hybrid interfaces are investigated for a model system composed of protoporphyrin IX (PPIX) as a stand-in for molecular catalysts and a variety of semiconductor substrates. Monolayers of PPIX are deposited using Langmuir-Blodgett deposition. Their morphology is studied in dependence of the deposition surface pressure to achieve a high-quality, dense coverage. By making use of ultraviolet-visible spectroscopy and ultraviolet photoelectron spectroscopy, the band alignment is determined by the vacuum level and incorporates an interface dipole of 0.4 eV independent of the substrate. The HOMO, LUMO, and LUMO+1 levels were determined to be at 5.6, 3.7, and 2.7 eV below the vacuum level, respectively. The quenching of PPIX photoluminescence in dependence of the potential gradient between excited state and electron affinity of the semiconductor substrates is overall in good agreement with electron transfer processes occurring at very fast time scales on the order of femtoseconds. Nevertheless, deviations from this model become apparent for narrower band gap semiconductors, which points to an additional relevance of other processes, such as energy transfer. These findings highlight the importance of matching the semiconductor to the molecular catalyst to prevent undesirable deactivation pathways.

Semiconductor Characterization by Terahertz Excitation Spectroscopy.

Surfaces of semiconducting materials excited by femtosecond laser pulses emit electromagnetic waves in the terahertz (THz) frequency range, which by definition is the 0.1-10 THz region. The nature of terahertz radiation pulses is, in the majority of cases, explained by the appearance of ultrafast photocurrents. THz pulse duration is comparable with the photocarrier momentum relaxation time, thus such hot-carrier effects as the velocity overshoot, ballistic carrier motion, and optical carrier alignment must be taken into consideration when explaining experimental observations of terahertz emission. Novel commercially available tools such as optical parametric amplifiers that are capable of generating femtosecond optical pulses within a wide spectral range allow performing new unique experiments. By exciting semiconductor surfaces with various photon energies, it is possible to look into the ultrafast processes taking place at different electron energy levels of the investigated materials. The experimental technique known as the THz excitation spectroscopy (TES) can be used as a contactless method to study the band structure and investigate the ultrafast processes of various technologically important materials. A recent decade of investigations with the THz excitation spectroscopy method is reviewed in this article. TES experiments performed on the common bulk A3B5 compounds such as the wide-gap GaAs, and narrow-gap InAs and InSb, as well as Ge, Te, GaSe and other bulk semiconductors are reviewed. Finally, the results obtained by this non-contact technique on low-dimensional materials such as ultrathin mono-elemental Bi films, InAs, InGaAs, and GaAs nanowires are also presented.

Emergence of tunable intersubband-plasmon-polaritons in graphene superlattices

On-demand modification of the electronic band structures of high-mobility two-dimensional (2D) materials is of great interest for various applications that require rapid tuning of electrical and optical responses of solid-state devices. Although electrically tunable superlattice (SL) potentials have been proposed for band structure engineering of the Dirac electrons in graphene, the ultimate goal of engineering emergent quasiparticle excitations that can hybridize with light has not been achieved. We show that an extreme modulation of one-dimensional (1D) SL potentials in monolayer graphene produces ladder-like electronic energy levels near the Fermi surface, resulting in optical conductivity dominated by intersubband transitions (ISBTs). A specific and experimentally realizable platform comprising hBN-encapsulated graphene on top of a 1D periodic metagate and a second unpatterned gate is shown to produce strongly modulated electrostatic potentials. We find that Dirac electrons with large momenta perpendicular to the modulation direction are waveguided via total internal reflections off the electrostatic potential, resulting in flat subbands with nearly equispaced energy levels. The predicted ultrastrong coupling of surface plasmons to electrically controlled ISBTs is responsible for emergent polaritonic quasiparticles that can be optically probed. Our study opens an avenue for exploring emergent polaritons in 2D materials with gate-tunable electronic band structures.

How Does Pseudo-Jahn-Teller Effect Induce the Photoprotective Potential of Curcumin?

In this paper, the molecular and electronic structure of curcumin is studied. High-symmetric gas-phase tautomers and their deprotonated forms in various symmetry groups are identified. The stability of lower-symmetry structures was explained by using the Pseudo-Jahn-Teller (PJT) effect. This effect leads to stable structures of different symmetries for the neutral enol and keto forms. The presented analysis demonstrated the potential significance of the PJT effect, which may modulate the setting of electronic and vibrational (vibronic) energy levels upon photodynamic processes. The PJT effect may rationalize the photoprotection action and activity of naturally occurring symmetric dyes.

Multipolar quantum electrodynamics of localized charge-current distributions: Spectral theory and renormalization

We formulate a nonrelativistic quantum field theory to model interactions between quantized electromagnetic fields and localized charge-current distributions. The electronic degrees of freedom are encoded in microscopic polarization and magnetization field operators whose moments are identified with the multipole moments of the charge-current distribution. The multipolar Hamiltonian is obtained from the minimal coupling Hamiltonian through a unitary transformation, often referred to as the Power-Zienau-Woolley transformation; we renormalize this Hamiltonian using perturbation theory, the result of which is used to compute the leading-order radiative corrections to the electronic energy levels due to interactions between the electrons and quantum vacuum fluctuations in the electromagnetic field. Our renormalized energy shift constitutes a generalization of the Lamb shift in atomic hydrogen, valid for general localized assemblies of atoms and molecules, possibly with net charge but absent a free current. By expanding the fields in a series of multipole moments, our results can be used to study contributions to this energy shift coming from specific multipole moments of arbitrary order.

Electron and hole spectrum taking into account deformation and polarization in the quantum dot heterostructure InAs/GaAs

In the paper InAs spherical quantum dots in a GaAs matrix were investigated. The energies of electrons and holes in single- and multi-band models (with strong, weak, and intermediate spin-orbit interaction) were calculated taking into account both the deformation of the quantum-dot matrix and the polarization charges on the quantum dot surface. The dependence of the energy levels of electrons and holes on the radius of the quantum dot is considered. It is shown that the deformation effects are stronger than polarization for the electron. For holes those effects are opposites. The energies of electrons and holes have been compared in all approximation models.

Hot carrier generation in a strongly coupled molecule–plasmonic nanoparticle system

Abstract In strongly coupled light matter systems electronic energy levels become inextricably linked to local electromagnetic field modes. Hybridization of these states opens new relaxation pathways in the system, particularly important for plasmon decay into single electron states, known as hot carriers. We investigate the influence of the coupling strength between a plasmonic resonator and a molecule on hot carrier generation using first principles calculations. An atomistic approach allows the capture of changes in the electronic structure of the system. We show that hot carriers are not only preferably generated at excitation frequencies matching the new polaritonic resonances, but their energy distribution strongly deviates from the one corresponding to the non-interacting system. This indicates existence of new plasmon decay paths due to appearance of hybridized nanoparticle–molecule states. We observe also direct electron transfer between the plasmonic nanoparticle and the molecule. Therefore, we may conclude, that bringing plasmonic nanostructures in strong interaction with molecules gives the ability to manipulate the energy distribution of the generated hot carriers and opens possibility for charge transfer in the system.

Synthesis, spectral, DFT, intrinsic constant of DNA binding and antioxidant activity of vanadyl (IV)2+ complexes of a symmetrical bisthiosemicarbazides

A new series of complexes were prepared by reacting vanadyl (II) sulphate with three multidentate bisthiosemicarbazides, TSCs in search for synthesizing a series of vanadyl complexes to be good candidates for utilization as anti-diabetic drugs. The TSCs 1(H4DDAT), 3 (H4DDET) and 5 (H4DDPT) were characterized by partial elemental analyses, 2DNMR, mass, FTIR and UV–vis. Spectra. The complexes were characterized by elemental analyses (C, H, N, S, M), spectral (FTIR, UV–vis., mass, ESR and XRD), magnetic susceptibility and molar conductivity measurements and assigned the formulae: [(VO)(H4DDAT) (H2O) (OH)]. H2O (2), [(VO)(H4DDET)(SO4)(H2O)].1·5H2O (4) and [(VO)(H4DDPT)(H2O)(SO4)2].2H2O (6). TSC`s were found to bind metal ion in keto or enol/thiol forms as neutral, monobasic or dibasic tridentate and / or hexadentate selective chelate as proved by the data of FTIR and NMR (heteronuclear single quantum coherence (HSQCNMR), correlated spectroscopy (COSY-NMR). UV–vis. and EPR data suggested a square pyramidal arrangement for complex (2) and an octahedral geometry for complexes (4) and (6), respectively. The anisotropic Lande splitting factor evaluated from EPR spectra for the complexes gave values; g|| < g⊥ < ge =2 0.0023. Orbital energy levels for magnetic electrons were determined from theoretically well fitted Spin Hamiltonian parameters. The thermal stability and nature of solvent molecules nature were studied by TGA and DrTGA. XRD data complex (2) suggested a triclinic complex (2); a cubic structure for complex (4) and a monoclinic for complex (6). Molecular modeling evaluated by DFT theory suggested oxygen atoms, N of NH or S of CS groups as donor atoms of TSc moiety and the geometry, Mullikan population, Mullikan charge and HOMO–LUMO gap were computed. Moreover, all compounds were screened for antioxidant activity such as SOD-like activity, scavenging of hydroxyl radicals as well as DNA binding ability.

Improving Accuracy and Transferability of Machine Learning Chemical Activation Energies by Adding Electronic Structure Information.

Predicting chemical activation energies is one of the longstanding and important challenges in computational chemistry. Recent advances have shown that machine learning can be used to create tools to predict them. Such tools can significantly decrease the computational cost for these predictions compared to traditional methods, which require an optimal path search along a high-dimensional potential energy surface. To enable this new route, we need both large and accurate datasets and a compact yet complete description of the reactions. Although data for chemical reactions is becoming increasingly available, the key step of encoding the reaction as an efficient descriptor remains a big challenge. In this paper, we demonstrate that including electronic energy levels in the description of the reaction significantly improves the prediction accuracy and transferability. Feature importance analysis further demonstrates that electronic energy levels have a higher importance than some structural information and typically require less space in the reaction encoding vector. In general, we observe that the results of the feature importance analysis relate well to the domain knowledge of fundamental chemical principles. This work can help to build better chemical reaction encodings for machine learning and thus improve the predictions of machine learning models for reaction activation energies. These models could ultimately be used to recognize reaction limiting steps in large reaction systems, allowing to account for bottlenecks at the design stage.

NIR emissions from Nd3+-activated phosphate-based glass system for cost-effective, tunable, and miniaturised laser devices

This work represents a phosphate-based glass system of composition (40-x) P2O5 − 30 B2O3 − 30 ZnSO4 - x Nd2O3, ( × = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) to determine the optical absorption and emission spectral characteristics. Moreover, Judd-Ofelt (J-O) intensity and radiative parameters were computed. Samples were prepared using melt-quenching method and characterized using Archimedes measurement, Ultraviolet–Visible-Near Infrared Spectroscopy and Photoluminescence Spectroscopy. The density values of these samples were reduced as the Nd2O3 concentration increased. The absorption spectra revealed 11 peaks corresponded to Nd3+ transitions from the lowest electronic energy level (4I9/2) to various excited levels. The optical energy band gap was found to be reduced with Nd3+ doping. The refractive indices (n) increased as the Nd3+ increase. The improving tendency of n was clarified in terms of the enhancing trend of samples molar volume (obtained from density), indicating a structural-optical correlation in the proposed glass system. The obtained values of Urbach energy (Eu) have an increasing trend in the range of ∼ 0.318–0.711 eV. Tow significant NIR emission peaks were assigned to the 4F5/2 → 4I9/2 and 4F3/2 → 4I9/2 transitions of Nd3+. Values of J-O intensity parameters Ω2, Ω4 and Ω6 were found in the range of (1.63–2.25)× 10−19 cm2, (2.57–2.94)× 10−19 cm2 and (1.53–1.82)× 10−19 cm2, respectively. The obtained stimulated emission cross-section for the NIR transitions from Nd3+ ((23.83–26.64)× 10−20 cm2 for 4F5/2 → 4I9/2, and (10.93–17.91)× 10−20 cm2 for 4F3/2 → 4I9/2 obviously revealed the lasing effectiveness of the titled glass system.

Optimization of Coherent Dynamics of Localized Surface Plasmons in Gold and Silver Nanospheres; Large Size Effects

Noble metal nanoparticles have attracted attention in recent years due to a number of their exciting applications in plasmonic applications, e.g., in sensing, high-gain antennas, structural colour printing, solar energy management, nanoscale lasing, and biomedicines. The report embraces the electromagnetic description of inherent properties of spherical nanoparticles, which enable resonant excitation of Localized Surface Plasmons (defined as collective excitations of free electrons), and the complementary model in which plasmonic nanoparticles are treated as quantum quasi-particles with discrete electronic energy levels. A quantum picture including plasmon damping processes due to the irreversible coupling to the environment enables us to distinguish between the dephasing of coherent electron motion and the decay of populations of electronic states. Using the link between classical EM and the quantum picture, the explicit dependence of the population and coherence damping rates as a function of NP size is given. Contrary to the usual expectations, such dependence for Au and Ag NPs is not a monotonically growing function, which provides a new perspective for tailoring plasmonic properties in larger-sized nanoparticles, which are still hardly available experimentally. The practical tools for comparing the plasmonic performance of gold and silver nanoparticles of the same radii in an extensive range of sizes are also given.

Tracing spatial confinement in semiconductor quantum dots by high-order harmonic generation

We report here on results of systematic experimental-theoretical investigation of high-order harmonic generation (HHG) in layers of CdSe semiconductor quantum dots of different sizes and a reference bulk CdSe thin film. We observe a strong decrease in the efficiency, up to complete suppression of HHG with energies of quanta above the band gap for the smallest dots, whereas the intensity of below band gap harmonics remains weakly affected by the dot size. In addition, it is observed that the suppression of the above gap harmonics is enhanced with increasing the driving wavelength. These systematic investigations allow us to develop a simple physical picture explaining the observed suppression of the highest harmonics: the discretization of electronic energy levels seems to be not the predominant contribution to the observed suppression but rather the confined dot size itself, causing field-driven electrons to scatter off the dot's walls. The reduction in the dot size below the classical electron oscillatory radius and the corresponding scattering limits the maximum acceleration by the laser field. Moreover, this scattering leads to a chaotization of motion, causing dephasing and a loss of coherence, therefore suppressing the efficiency of the emission of highest-order harmonics. Our results demonstrate a regime of intense laser-nanoscale solid interaction, intermediate between the bulk and single-molecule response, and are crucial for nanophotonic platforms aiming at control over high-order harmonic properties and efficiency.

Long-Lived Multiple Charge Separation by Proton-Coupled Electron Transfer.

Multiple charge separation has been successfully realized by a proton-coupled electron transfer reaction in an organic cocrystal. Benefiting from the adjustable electronic energy level of the electron donor and acceptor through thermal-induced proton migration, distinct optical absorption behaviors combined with color changes to blue or green are observed in these charge-separated states. It is of interest to note that such charge-separated states exhibit a longer lifetime of over a month as a result of the excellent coplanarity and π-π interaction of the electron acceptors. Moreover, the enhanced absorption toward longer wavelengths endows the charge-separated state with near-infrared (808 nm) photothermal conversion for imaging and bacterial inhibition, whereby the conversion performance can be controlled by the degree of proton migration.

Long‐Lived Multiple Charge Separation by Proton‐Coupled Electron Transfer

AbstractMultiple charge separation has been successfully realized by a proton‐coupled electron transfer reaction in an organic cocrystal. Benefiting from the adjustable electronic energy level of the electron donor and acceptor through thermal‐induced proton migration, distinct optical absorption behaviors combined with color changes to blue or green are observed in these charge‐separated states. It is of interest to note that such charge‐separated states exhibit a longer lifetime of over a month as a result of the excellent coplanarity and π‐π interaction of the electron acceptors. Moreover, the enhanced absorption toward longer wavelengths endows the charge‐separated state with near‐infrared (808 nm) photothermal conversion for imaging and bacterial inhibition, whereby the conversion performance can be controlled by the degree of proton migration.

Charge transport mechanism of cross‐linked polyethylene/silicone rubber composite insulation by energy band theory

AbstractThe composite insulation composed of cross‐linked polyethylene (XLPE) and silicone rubber (SiR) is common in high voltage direct current cable accessory installation. However, the space charge accumulation, especially the interfacial charge accumulation of XLPE/SiR, poses a serious threat to the safe operation of cable accessories, and its charge transport mechanism is still unclear, especially at the micro‐scale. In order to investigate the charge transport mechanism of XLPE/SiR, simultaneous measurement of space charge and relaxation current is performed on XLPE/SiR at various electric fields with different polarities, and the electronic energy levels of XLPE and SiR are determined by quantum chemical calculation (QCC). The results of QCC show that both the hole traps and the electron traps in XLPE are mainly shallow traps. As for SiR, the hole traps are shallow traps, while the electron traps are deep traps. The results of simultaneous measurement show that the interfacial charge accumulation and the composite conductivity of XLPE/SiR are significantly different under different polarities, that is, there is an obvious polarity effect. Based on the results of QCC, the electronic energy levels of XLPE/SiR system are constructed considering the interface between XLPE and SiR, as well as the interfaces between the materials and the electrodes. On this basis, the charge transport mechanism of XLPE/SiR is discussed in detail, and the polarity effect is well explained, which is believed to be related to the differences in the charge injection barrier and the interfacial barrier under different polarities, as well as the electron/hole traps in XLPE and SiR.

Tungsten bronze CsxWO3 nanopowders doped by Ti to enhance transparent thermal insulation ability for energy saving

Cesium tungsten bronze (CsxWO3), a unique energy-saving material, has attracted great interest because of its excellent visible transmittance and near-infrared absorption. In order to improve its optical properties, the Ti doping modification was carried out in this work, and a series of Ti-doped CsXWO3 (Ti-CsxWO3) nanopowders were synthesized by a solvothermal reaction and post-annealing. The 1.71 at. % of Ti dopants achieved remarkable enhancement of both integral visible transmittance (Tlum, 380–780 nm) and near-infrared shielding efficiency (ΨNIR, 780–2500 nm) of CsxWO3. The Tlum and ΨNIR of the 1.71 at. % Ti-CsxWO3 polymer film reaches 63.87 % and 76.90 %, respectively, higher by 51.88 % and 65.00 % than those of the CsxWO3 film. The improvement of Tlum is attributed to the broadening of band gap and smaller size of the nanoparticles induced by Ti doping, and the enhanced ΨNIR would result from the increased free electron concentration and energy levels of impurities. The incorporation of Ti elements renders CsxWO3 a promising application in the field of energy saving.

Critical Crystallographic Transition in Violation of Kasha’s Rule of Size-Specific ZnO Quantum Dots

Investigation of the intrinsic relationship between crystallography and electronic properties may provide an avenue to unravel the photophysical aspects of semiconductor nanostructures. Since the 1980s, semiconducting materials at the nanoscale dimensions have been of immense scientific interest because of the unique quantum characteristics beyond a particular size limit. Prudent advances in the synthetic strategies of naked ZnO quantum dots have offered the opportunity to imbue the structure–property relationship of nanostructured systems. Seven size-specific ZnO nanospheres have been synthesized through alkaline hydrolysis of the precursor salt in the presence of alcohol in the reaction medium. The photoluminescence behavior of colloidal dispersion of ZnO nanoparticles has been studied as a function of excitation wavelength with a periodic interval of 10 nm in the range of 290–430 nm. It has been observed that changes in the excitation wavelength shift the emission spectrum in a regular manner independent of the size of ZnO particles under investigation. The empirical proposition in the framework of Kasha’s rule has been established as a milestone of spectroscopy, being validated in tens of thousands of fluorophore systems; meanwhile, although obscure, anomalous cases have also been observed both in molecular and nanoscale systems. Crystallographic analysis has shown that there occurs a structural transition that determines the localization of electronic energy levels in the experimental size range of the ZnO particles. Therefore, the salient feature of physical significance is that crystallographic transition appears to exhibit the excitation wavelength-dependent shift of the photoluminescence maximum and is therefore the violation of Kasha’s rule for the ZnO quantum dots.