Electronic Transitions Research Articles

Observation of Hydrostatic‐Pressure‐Modulated Giant Caloric Effect and Electronic Topological Transition

AbstractPhase transition is a fundamental phenomenon in condensed matter physics, in which states of matter transform to each other with various critical behaviors under different conditions. The magnetic martensitic transformation features significant multi‐caloric effects that benefit the solid‐state cooling or heat pumping. Meanwhile, the electronic topological transition (ETT) driven by pressure has been rarely reported in martensitic systems. Here, the modulation effects of hydrostatic pressure on phase transitions in a magnetic martensitic alloy are reported. Owing to the huge volume expansion during the transition, the martensitic transition temperature is driven from 339 to 273 K by pressure within 1 GPa, resulting in highly tunable giant baro‐ and magneto‐caloric effects (BCE and MCE) in a wide working temperature range. Interestingly, an ETT is further induced by pressure in the martensite phase, with a sudden drop of the measured saturation magnetization around 0.6 GPa. First‐principles calculations reveal a sharp change in the density of states (DOS) due to the orbit shift around the Fermi level at the same pressure and reproduce the experimental observation of magnetization. Besides, the ETT is accompanied by remarkable changes in the lattice parameters and the unit‐cell orthorhombicity. The study provides insight into pressure‐modulated exotic phase‐transition phenomena in magnetic martensitic systems.

Anthocyanins of Delonix Regia Floral Petals: A Novel Approach on Fluorescence Enhancement, Forster Resonance Energy Transfer Mechanism and Photostability Studies for Optoelectronic Applications.

In this work, we focused on extracting the anthocyanin dye in acetone, butanol, ethanol, and water solvents from Delonix regia flowers by a simple maceration extraction process. The identification of functional group analysis, vibrational studies, energy transfer mechanisms, optoelectronic properties, photostability studies, FRET-assisted potential light emissions and photometric properties of the anthocyanin dyes are successively investigated. FTIR spectroscopy and vibrational studies have confirmed the existence of polyphenolic groups in 2-phenyl chromenylium (anthocyanin) dyes. The optoelectronic results show the least direct bandgap (2.04eV), indirect bandgap (1.55eV), Urbach energy (0.380eV), high refractive index (1.20), dielectric constant (2.794), and high optical conductivity (1.954 × 103 S/m) for the anthocyanin dye extracted found in water solvent. The photoluminescence properties such as Stoke's shift, high quantum yield, and lifetime results show that anthocyanin dyes are promising candidates for red-LEDs and optical materials. The absorption and emission spectra of the anthocyanin dyes follow the mirror image rule and the Franck-Condon factor exists between vibrational energy levels corresponding to all the electronic transitions. The excellent correspondence between the absorption and emission spectra reinforces that the anthocyanins are efficient (46%) FRET probes. Further, photometric properties such as CIE, CRI, CCT and colour purity results of anthocyanins in all studied solvents revealed that this material exhibits orange to red shades (x = 0.48 → 0.54 and y = 0.36 →0.45) and is well suitable for have great potential in the manufacturing of Organic-LEDs and other optoelectronic device applications.

Orthogonal effect of exchange and correlation parameters in density functional theory to compute geometric and spectroscopic quantities.

The influence of the composition of the functional used for density functional theory computations on one structural parameter (a dihedral angle) and a spectroscopic parameter (absorption wavelength) is assessed in this study on the basis of two molecules (flavonols). In this kind of molecules, these two parameters should be correlated according to the nature of the electronic transition involved. However, it is shown herein that by varying the proportion of true exchange and correlation while building a functional, it is possible to obtain independently a large range of values for these parameters without any relation with the underlying real values. Therefore, it is concluded that the choice of a functional after a benchmark, especially using user-defined functionals, should be carried out with great care to avoid such effects.

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Uncovering the Potential of Industrial Waste: Turning Discarded Resources into Sustainable Advanced Materials

Abstract To identify solutions for utilizing industrial wastes (slag, sludge, fly ash, and bottom ash) in the development of pro-environmental systems, this paper reviews existing literature and explores material characterization methods. A review analysis was conducted to uncover their potential, and it was found that many utilizations can be made to recycle them into sustainable materials. Structure characterization, optical-dielectric function, and morphology analysis were analyzed to confirm the recent review. Structural properties are represented by crystallite size and crystallinity, where nickel slag shows the smallest distribution (55±10) nm with the highest crystallinity (25.42%), indicating its association with uniformity of response to external disturbances and micro-structural stability. From the analysis of optical and dielectric functions via Kramers Kronig relation, the widening of ∆(LO-TO) was shown by fly ash and slag indicating stable bonding suitable as x-ray shielding and sensor, while high electron loss functions were shown by sludge and bottom ash indicating high potential electronic transition performance. Based on their chemical and physical properties, these industrial wastes are not limited as construction materials and can even be upgraded to more advanced development materials.

High-temperature concomitant metal-insulator and spin-reorientation transitions in a compressed nodal-line ferrimagnet Mn3Si2Te6

Symmetry-protected band degeneracy, coupled with a magnetic order, is the key to realizing novel magnetoelectric phenomena in topological magnets. While the spin-polarized nodal states have been identified to introduce extremely-sensitive electronic responses to the magnetic states, their possible role in determining magnetic ground states has remained elusive. Here, taking external pressure as a control knob, we show that a metal-insulator transition, a spin-reorientation transition, and a structural modification occur concomitantly when the nodal-line state crosses the Fermi level in a ferrimagnetic semiconductor Mn3Si2Te6. These unique pressure-driven magnetic and electronic transitions, associated with the dome-shaped Tc variation up to nearly room temperature, originate from the interplay between the spin-orbit coupling of the nodal-line state and magnetic frustration of localized spins. Our findings highlight that the nodal-line states, isolated from other trivial states, can facilitate strongly tunable magnetic properties in topological magnets.

Corporate learning in a disruptive digital era: a new global organizational paradigma (A case-study of IBM’s Your Learning Platform)

In a digital world when the technologies as well as the market places are evolving at an alarming pace, facilitating the employees to acquire newer knowledge and helping them advance their learning is most challenging than ever before. Staying agile and to become and remain ahead of competition in this swiftly changing business landscape is a daunting task indeed for companies. Corporate universities and Classrooms in B-schools have totally been overshadowed and got undermined by newer versions of learning and we are witnessing that the buffet of teaching employees is expanding and changing more than ever before. In addition to tracking down a plethora of in-person opportunities in the form of mentorships and training, employees are able to use their computers and smart phones to sift through facilely rich content online at any time and place. It may be in the form of online social media networks, published papers, as well as videos and courses. Nowadays, mobile and cloud technologies, and social networks are taken for granted by the tech-savvy modern employees. And not surprisingly, the millennials believe that technology makes them more effective and productive and hence always prefer to communicate through the electronic mode at workplace than face to face or for that matter even the telephone. They are found to be using technology only routinely. This Paper addresses the important challenge of shifting learning to the 21st Century platform economy faced by corporates and discusses how IBM has successfully tackled the same through its Your Learning Platform.

Effects of La-N Co-Doping of BaTiO3 on Its Electron-Optical Properties for Photocatalysis: A DFT Study

In cation–anion co-doping, rare earth elements excel at regulating the electronic structure of perovskites, leading to their improved photocatalytic performance. In this regard, the impact of co-doping rare earth elements at the Ba and Ti sites in BaTiO3 on its electronic and photocatalytic properties was thoroughly investigated based on 2 × 2 × 2 supercell structures of BaTiO3 with different La concentrations of 12.5% and 25% using DFT calculations. The band structure, density of states, charge density difference, optical properties, and the redox band edge of the co-doped models mentioned above were analyzed. The results indicated that the BaTiO3 structure co-doped with 25% La at the Ti site exhibited higher absorption in the visible range and displayed a remarkable photocatalytic water-splitting performance. The introduced La dopant at the Ti site effectively reduced the energy required for electronic transitions by introducing intermediate energy levels within the bandgap. Our calculations and findings of this study provide theoretical support and reliable predictions for the exploration of BaTiO3 perovskites with superior photocatalytic performances.

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Multiphoton Ionization/Dissociation of Molecular Sulfur S2 in the UV Region.

The multiphoton ionization/dissociation dynamics of molecular sulfur (S2) in the ultraviolet range of 205-300 nm is studied using velocity map ion imaging (VMI). In this one-color experiment, molecular sulfur (S2) is generated in a pulsed discharge and then photodissociated by UV radiation. At the three-photon level, superexcited states are accessed via two different resonant states: the B3Σu- (v' = 8-11) valence states at the one-photon level and a Rydberg state at the two-photon level. Among the decay processes of these superexcited states, dissociation to electronically excited S atoms is dominant as compared to autoionization to ionic states S2+ (X2Πg) at wavelengths λ < 288 nm. The anisotropy parameter extracted from these images reflects the parallel character of these electronic transitions. In contrast, autoionization is found to be particularly efficient at S(1D) and S(1S) detection wavelengths around 288 nm. Information obtained from the kinetic energy distributions of S atoms has revealed the existence of vibrationally excited S2+ (X2Πg (v+ > 11)) that dissociates to ionic products following one-photon absorption. This work also reveals many interesting features of S2 photodynamics compared to those of electronically analogous O2.

Investigation on the hydrogen storage properties, electronic, mechanical properties, debye temperature of H24AlXO20S2 (X=Na, Rb, Cs, K) hydrides

The stability and lattice vibration of H24AlXO20S2 (X = Na, Rb, Cs, K) hydrides are predicted by calculating the crystal structure and energy. The formation enthalpy proves the structural stability and the dynamic stability of the hydride is predicted by the phonon dispersion diagram. Meanwhile, the optical and mechanical properties are analyzed by using the quasi-Debye model. The elastic constants and modulus prove H24AlXO20S2 (X = Na, Rb, Cs, K) mechanical stability. By the value of B/G and Poisson's ratio, it inferred that H24AlNaO20S2, H24AlRbO20S2 and H24AlKO20S2 are brittle. Only H24AlCsO20S2 is ductile and has the lowest hardness. H24AlRbO20S2 has the largest shear modulus and Young's modulus, so it has the highest hardness. In addition, by calculating the anisotropy index of the hydrides, it is proved that they are anisotropic. H24AlKO20S2 has the strongest anisotropy and the value of AU is 0.2477. The anisotropy of the hydride is further studied by calculating the Debye temperature and sound velocity of H24AlXO20S2 (X = Na, Rb, Cs, K) hydrides. The energy band and state density analysis reveal their electronic transitions and bonding.

Significant Enhancement of Electrocaloric Effect in Ferroelectric Polycrystalline Ceramics Through Grain Boundary Barrier Engineering

AbstractA key challenge currently for the new ferroelectric refrigeration with high efficiency and environmental friendliness lies in the urgent demand for ferroelectric materials with huge electrocaloric effects (ECE). Ferroelectric polycrystalline ceramics with high ECE stand out as one of the most promising candidates for electrocaloric cooling applications. However, the grain boundary network, as a barrier for the cross‐transmission of charged carriers, widely exists in electrocaloric polycrystalline ceramics and is often neglected in favor of focusing more on composition regulation and structural design. Herein, a grain boundary barrier engineering is proposed that regulates the Schottky barrier at the grain boundary network in the Ba0.8Zr0.2TiO3 ceramics by a maneuverable annealing process and clarifies its critical role in enhancing the ECE of polycrystalline ceramics. As a result, a substantial enhancement of the EC performance (from 0.68 to 1.63 K at 50 °C and 80 kV cm−1, ≈2.4 times) has been achieved in the annealed Ba0.8Zr0.2TiO3 ceramics with a lower Schottky barrier. The microstructural and electrical characterization reveals that the lower Schottky barrier in the grain boundary network facilitates the domain switching and electronic transition, hence resulting in enhanced polarization response and EC performance.

Exploring hot carrier relaxation dynamics in MoSi2N4 monolayer for photocatalytic applications: Insights into electron-phonon coupling mechanisms

The relaxation process of hot carriers in MoSi2N4 monolayer remains unclear due to the need to sample electron–phonon interaction at different momenta. Utilizing density functional theory (DFT) combined with nonadiabatic molecular dynamics (NAMD), we determined that the material possesses an indirect bandgap of approximately 2.33 eV, primarily originating from the d orbitals of inner Mo atoms. NAMD simulations unveil rapid relaxation of hot electrons and holes, exhibiting lifetimes of approximately 166 fs and 146 fs, respectively. The rapid relaxation of hot carriers couples with the vibrations of outer Si and N atoms, with no inter-valley scattering observed between the K and K′ valleys. Notably, the coupling between the d orbitals of inner Mo atoms and the vibrations of outer Si and N atoms plays a pivotal role in determining the relaxation dynamics of hot carriers, shedding light on the intricate interplay between electronic and vibrational modes in this material. Our research reveals the potential application value of MoSi2N4 monolayer material as a photocatalyst and elucidates a relaxation mechanism governing the dynamics of excited carriers.

Effects of electrical stimulation on carbon sequestration of photosynthetic bacteria: Response of the photosynthetic unit to electrical stimulation

Bioelectrochemical systems have been used to enhance the carbon sequestration of photosynthetic bacteria (PSB), but it is unclear whether the electrical stimulation affects the structure of membrane proteins involved in photochemical activity. In this study, the rate of CO2 fixation in the photosynthetic bacteria R. palustris increased with electrical stimulation, and the enhancement partly remained even after the power off. The CO2 fixation rate in electrical-stimulated PSB was 10% higher than in non-stimulated PSB, and the activity of the CO2 fixation enzyme Rubisco was 16% higher. This resulted from the improved light utilization efficiency of the photosynthetic units in R. palustris after electrical stimulation, particularly due to the enhancement of the primary reaction mediated by the light capture protein RC-LH1. The molar extinction coefficient of the light capture protein RC-LH1 increased from 3301 cm−1 mM−1 to 3733 cm−1 mM−1, and the maximum rate of the primary reaction increased from 6.88 × 10−3 e−RC−1s−1 to 8.66 × 10−3 e−RC−1s−1. Circular dichroism spectroscopy and Fourier transform infrared spectroscopy indicated that the electrical stimulation increased the dipole moment of the α-helix in RC-LH1 to facilitate the quinone transport in the primary reaction. Nuclear magnetic resonance spectroscopy revealed that the electrical stimulation increased the formation of hydrogen bonds in bacteriochlorophyll a for electron transition. This study investigated the response of photosynthetic bacteria to electrical stimulation, providing a distinct outlook on the electrochemical regulation of photosynthesis for carbon capture.

Nitrogen‐Rich Carbon Dot‐Mediated n→π* Electronic Transition in Carbon Nitride for Superior Photocatalytic Hydrogen Peroxide Production

AbstractSolar‐driven synthesis of hydrogen peroxide (H2O2) through photocatalysis stands out as a promising avenue for sustainable energy generation, marked by environmental friendliness and industrial feasibility. However, the inherent limitations of carbon nitride (CN) in photocatalytic H2O2 production significantly impede their performance. Herein, a novel 0D/2D carbon dots‐modified CN nanosheet heterojunction (CDsMCN) is introduced, synthesized through a hydrothermal‐calcination tandem strategy induced by CDs derived from melamine. This innovative technique enhances the n→π* electronic transition in CDsMCN, accelerating the separation efficiency of electron‐hole pairs, boosting oxygen adsorption, and promoting a highly selective 2e− ORR. Comparative to pristine CN, CDs10MCN exhibited a remarkable tenfold increase in H2O2 production, reaching an impressive 1.48 mmol L−1. Furthermore, CDs10MCN demonstrates exceptional stability, maintaining its catalytic efficiency at the initial level over four consecutive cycles. The notable achievement of a molar selectivity of H2O2 ≈80% at an onset potential of 0.6 V (vs RHE) underscores its exceptional ability to produce the desired product selectively. Advanced in situ characterization together with DFT calculations revealed that the ultrathin CDs10MCN nanosheet heterojunction with enhanced n→π* electronic transition improves its optical properties, reduces bandgap, facilitates fast charge migration, and increases photocatalytic H2O2 performance, thereby serving as a promising candidate for advanced catalytic applications.

Self-enhanced regulation of stable organic radicals with polypeptide nanoparticles for mild second near-infrared phototheranostics

Stable organic radicals have emerged as a promising option to enhance fluorescence quantum yield (QY), gaining traction in medical treatment due to their unique electronic transitions from the ground state (D0) to the doublet excited state (D1). We synthesized a stable dicyanomethyl radical with a NIR-II fluorescence QY of 0.86 %, surpassing many NIR-II organic dyes. Subsequently, amphiphilic polymer-encapsulated nanoparticles (NPs) containing the radical were created, achieving a NIR-II fluorescence QY of 0.32 %, facilitating high-contrast bio-imaging. These CNPPs exhibit self-enhanced photothermal properties, elevating photothermal conversion efficiency (PCE) from 43.5 % to 57.5 % under 915 nm laser irradiation. This advancement enables more efficient photothermal therapy (PTT) with lower dye concentrations and reduced laser power, enhancing both feasibility and safety. Through regular fractionated mild photothermal therapy, we observed the release of damage-associated molecular patterns (DAMPs) and an increase in cytokine expression, culminating in combined mild phototherapy (m-PTT)-mediated immunogenic cell death (ICD). Consequently, we developed an immunostimulatory tumor vaccine, showcasing a novel approach for refining photothermal agents (PTA) and optimizing the PTT process.

Instantaneous Marcus theory for photoinduced charge transfer dynamics in multistate harmonic model systems

Modeling the dynamics of photoinduced charge transfer (CT) in condensed phases presents challenges due to complicated many-body interactions and the quantum nature of electronic transitions. While traditional Marcus theory is a robust method for calculating CT rate constants between electronic states, it cannot account for the nonequilibrium effects arising from the initial nuclear state preparation. In this study, we employ the instantaneous Marcus theory (IMT) to simulate photoinduced CT dynamics. IMT incorporates nonequilibrium structural relaxation following a vertical photoexcitation from the equilibrated ground state, yielding a time-dependent rate coefficient. The multistate harmonic (MSH) model Hamiltonian characterizes an organic photovoltaic carotenoid-porphyrin-fullerene triad dissolved in explicit tetrahydrofuran solvent, constructed by mapping all-atom inputs from molecular dynamics simulations. Our calculations reveal that the electronic population dynamics of the MSH models obtained with IMT agree with the more accurate quantum-mechanical nonequilibrium Fermi’s golden rule. This alignment suggests that IMT provides a practical approach to understanding nonadiabatic CT dynamics in condensed-phase systems.

Quantum jumps in driven-dissipative disordered many-body systems

Quantum jumps in driven-dissipative disordered many-body systems

Model expressions for refractive indices of electron waves in cold magnetoactive plasma of arbitrary density

Despite the undoubted importance of having fairly simple analytical expressions for the refractive indices of wave modes in a magnetoactive plasma, such expressions are known only in some particular cases. For electron waves with frequencies much higher than the lower hybrid resonance frequency, such an expression is known only for whistler waves in a dense plasma when the electron plasma frequency significantly exceeds the electron cyclotron frequency. In this Letter, we propose simple operational expressions for the refractive indices of all four electron modes in a magnetoactive plasma, namely, the fast magnetosonic, also called whistler mode, the slow extraordinary mode, the ordinary mode, and the fast extraordinary mode. The form of these expressions does not depend on the value of the ratio of plasma frequency to cyclotron frequency.

DFT and TD‐DFT Study of Many‐Body and Hydrogen Bonding Interactions: Nitrosamine Oligomers

AbstractThis study focuses on the properties and intermolecular interactions of nitrosamine oligomers, which are important in both semiconductor manufacturing and nuclear waste management. The study explores various configurations of nitrosamine oligomers, ranging from monomers to pentamers in linear, ladder, and cyclic clusters, with the finding that dimer cyclic forms and hexamers and above are unstable. Many‐body analysis revealed that two‐body interaction energies made remarkable contributions to the binding energy, while the sum of 3‐, 4‐, and 5‐body energy contributed less, indicating the decrease in stability of nitrosamine from dimer to pentamer clusters. Using advanced computational techniques, such as dispersion‐corrected B3LYP‐D3 and TD‐DFT, the study investigates the vibrational modes and electronic absorption spectra of nitrosamine oligomers. The results reveal that different configurations can significantly affect the vibrational modes and electronic properties of nitrosamine oligomers. The NH2 symmetric and asymmetric modes were particularly intense in various forms of nitrosamine oligomers. The wavelengths of electronic transition, oscillator strength, and HOMO to LUMO gap were reported. Additionally, the study reports on nitrosamine oligomers’ hydrogen‐bonded cooperativity and binding energy contributions. Overall, these findings offer valuable insights into the stability and properties of nitrosamine oligomers, with potential applications in materials science and chemical engineering.