Search

The current research depicts the laser irradiation-induced effect on the optoelectrical and structural properties of thermally evaporated Bi15In20Se65 thin films with different exposure durations (0, 10, 20, 30, 60, and 90 min). The illumination effect under different lasing times leads to the retention of amorphous nature, indicating the short-range ordering inside the matrix. An improvement in the homogeneous and smooth texture of the film surface even after irradiation has been observed. However, significant optical changes have been noticed with different exposure durations. Transparency decreased with the exposure time, whereas an increment in the absorption coefficient with red shifting in the absorption edge was observed. Broad transparency and less absorption over the infrared region make these films promising for infrared optics such as temperature detection, energy management, monitoring, night vision, etc. Laser illumination allowed bond rearrangements that led to an increase in defect states over the forbidden gap regime and reduced the bandgap from 1.02 to 0.94 eV, confirming the photodarkening nature. This consequently enhanced the Urbach energy and electron–phonon interactions. Both extinction coefficient and refractive index enhanced with lasing duration, indicating an increment in the scattering centers with the lasing duration. The increase in the lasing time results in the increase of interband transitions, which might be due to the increase of carrier concentrations in the system. The non-linear susceptibility (χ(3)) and refractive indices showed enhancement with exposure duration. The observed non-linear refractive index (SI) is 20–30 times greater than silica. This reduction of Eg and enhancement in non-linearity improves the occurrence of two-photon absorption, signifying the potentiality for photonic devices. The hydrophilic nature of laser-irradiated films makes them suitable for applications such as self-cleaning, antifouling, and antifogging as coating materials. [ABSTRACT FROM AUTHOR]

First-principles simulations were conducted to explore various electronic properties of crystalline SiO2 (α-quartz) under ultrafast laser irradiation. Employing Density Functional Perturbation Theory and the many-body (GW) approximation, we calculated the impact of thermally excited electrons on the electronic specific heat, electron pressure, effective mass, deformation potential, electron-phonon coupling and electron relaxation time of quartz, covering a wide range of electron temperatures, up to 100,000 K. We show that the electron-phonon relaxation time of highly-excited quartz becomes twice faster compared to low-excited states. The deformation potential, which dictates atomic displacement, has a non-monotonic behavior with a well-pronounced minimum at around 16,000 K (2.7 × 1021 cm−3 of excited electrons) where the bond ionicity of the Si-O starts decreasing followed by a cohesion loss at 35,000 K due to the pressure exerted by the excited electrons on the lattice. Consequently, our calculated data, illustrating the evolution of physical parameters, can facilitate simulations of laser-matter interactions and provide predictive insights into the behavior of quartz under experimental conditions. [ABSTRACT FROM AUTHOR]

In this study, a novel thermally stability broad-band near-infrared (NIR) phosphor SrLaMgTaO 6 (SLMT): Cr3+ was research, along with investigations into its structure, morphology, PL spectra and crystal field strengths. Additionally, the mechanism of concentration quenching in these samples was investigated, which primarily attributed to electric multipolar interactions notably. Surprisingly, the NIR emission intensity at 423 K remains 80.4 % of its room temperature intensity, which shows its outstanding thermal stability. To comprehend the mechanism behind the exceptional thermal stability of luminescence, a comprehensive analysis in this material was conducted, focusing on factors such as the crystal field strength of the host material and the electron-phonon coupling (EPC) effect. Subsequently, an optimized phosphor coating was applied to a 470 nm LED chip to get a NIR pc-LED device, which was evaluated for its performance. The research demonstrate that SLMT: Cr3+ phosphor is a promising NIR pc-LED. [ABSTRACT FROM AUTHOR]

Hydrogen in metals is a significant research area with far-reaching implications, encompassing diverse fields such as hydrogen storage, metal-insulator transitions, and the recently emerging phenomenon of room-temperature superconductivity under high pressure. Hydrogen atoms pose challenges in experiments as they are nearly invisible, and they are considered within ideal crystalline structures in theoretical predictions, which hampers research on the formation of metastable hydrides. Here, we propose pressure-induced hydrogen migration from tetrahedral (T-) site to octahedral (O-) site, forming LaH x O H 2 − x T in cubic LaH2. Under decompression, it retains H x O occupancy, and is dynamically stable even at ambient pressure, enabling a synthesis route of metastable dihydrides via compression-decompression process. We predict that the electron-phonon coupling strength of LaH x O H 2 − x T is enhanced with increasing x, and the associated Tc reaches up to 10.8 K at ambient pressure. Furthermore, we calculated stoichiometric hydrogen migration threshold pressure (Pc) for various lanthanides dihydrides (RH2, where R = Y, Sc, Nd, and Lu), and found an inversely linear relation between Pc and ionic radii of R. We propose that the highest Tc in the face-centered-cubic dihydride system can be realized by optimizing the O/T-site occupancies. [ABSTRACT FROM AUTHOR]

In our pursuit of understanding electron-phonon coupling (EPC) and their impact on material properties, we delved deep into the intricate role played by the Eliashberg function in governing electron self-energy. Through meticulous evaluation of tailored polynomial models approximating this function, we unearthed profound insights into how phonon interactions intricately modify electronic energy bands. Employing numerical computations, we meticulously unraveled both the real and imaginary aspects of electron self-energy, crucial in comprehending EPC effects in various materials. Investigating superconductivity within monolayer graphene and its interaction with diverse doping substances, our study led us to identify optimal polynomial models that accurately capture EPC behaviors, offering invaluable implications for predicting critical temperatures in superconducting materials. Expanding the parameters within our models allowed us to anticipate changes in self-energy models for higher-order configurations not explored in this study. Our selection of polynomial spanning degrees from n = 1 to 10 the efficacy of n = 2 (Debye) as the most realistic and accurate model, closely followed by n = 1, albeit occasional deviations observed in specific materials. These discrepancies often stemmed from noise model inaccuracies and parameter approximations. Our comprehensive approach outshone the traditional Kramer-Kronig transform in assessing electron-phonon interactions. Looking ahead, the application of multiple models to the Eliashberg function diagram holds immense promise for enhancing accuracy, despite the challenge of concurrently adjusting multiple input parameters. This integration of numerical modeling with experimental data forms a robust framework, empowering the prediction and fine-tuning of material properties vital for the future fabrication of devices. [ABSTRACT FROM AUTHOR]

VS2 and VSe2 have attracted particular attention among the transition metals dichalcogenides because of their promising physical properties concerning magnetic ordering, charge density wave (CDW), emergent superconductivity, etc., which are very sensitive to stoichiometry and dimensionality reduction. Yanson point-contact (PC) spectroscopic study reveals metallic and nonmetallic states in VS2 PCs, as well as a magnetic phase transition, was detected near 20 K. The rare PC spectra, where the magnetic phase transition was not visible, show a broad maximum of around 20 mV, likely connected with electron-phonon interaction (EPI). The PC spectra of VSe2 demonstrate metallic behavior, which allowed us to detect features associated with EPI and CDW transition. The Kondo effect appeared for both compounds, apparently due to interlayer vanadium ions. Besides, the resistive switching was observed in PCs on VSe2 between a low resistive, mainly metallic-type state, and a high resistive nonmetallic-type state by applying bias voltage (about 0.4 V). Reverse switching occurs by applying a voltage of opposite polarity (about 0.4 V). The reason may be the alteration of stoichiometry in the PC core due to the displacement of V ions to interlayer under a high electric field. The observed resistive switching characterizes VSe2 as a potential material, e.g., for non-volatile resistive RAM, neuromorphic engineering, and other nanoelectronic applications. Per contra, VS2 attracts attention as a rare layered van der Waals compound with magnetic transition. [ABSTRACT FROM AUTHOR]

A recent theoretical study (Xu in Proc R Soc A Math Phys Eng Sci 477:20200913, 2021) has derived conditions on the coefficients of Jeffreys-type equation to predict thermal oscillations and resonance during phonon hydrodynamics in non-metallic solids. Thermal resonance, in which the temperature amplitude attains a maximum value (peak) in response to an external exciting frequency source, is a phenomenon pertinent to the presence of underdamped thermal oscillations and explicit finite speed for the thermal wave propagation. The present work investigates the occurrence condition for thermal resonance phenomenon during the electron–phonon interaction process in metals based on the hyperbolic two-temperature model. First, a sufficient condition for underdamped electron and lattice temperature oscillations is discussed by deriving a critical frequency (a material characteristic). It is shown that the critical frequency of thermal waves near room temperature, during electron–phonon interactions, may be on the order of terahertz ( 10 - 20 THz for Cu and Au, i.e., lying within the terahertz gap). It is found that whenever the natural frequency of metal temperature exceeds this frequency threshold, the temperature oscillations are of underdamped type. However, this condition is not necessary, since there is a small frequency domain, below this threshold, in which the underdamped thermal wave solution is available but not effective. Otherwise, the critical damping and the overdamping conditions of the temperature waves are determined numerically for a sample of pure metals. The thermal resonance conditions in both electron and lattice temperatures are investigated. The occurrence of resonance in both electron and lattice temperature is conditional on violating two distinct critical values of frequencies. When the natural frequency of the system becomes larger than these two critical values, an applied frequency equal to such a natural frequency can drive both electron and lattice temperatures to resonate together with different amplitudes and behaviors. However, the electron temperature resonates earlier than the lattice temperature. [ABSTRACT FROM AUTHOR]

The interaction between lattice vibrations and electrons plays a key role in various aspects of condensed matter physics — including electron hydrodynamics, strange metal behavior, and high-temperature superconductivity. In this study, we present systematic investigations using Raman scattering and angle-resolved photoemission spectroscopy (ARPES) to examine the phononic and electronic subsystems of the topological superconductor candidate 2M-WS2. Raman scattering exhibits an anomalous nonmonotonic temperature dependence of phonon linewidths, indicative of strong phonon–electron scattering over phonon–phonon scattering. The ARPES results demonstrate pronounced dispersion anomalies (kinks) at multiple binding energies within both bulk and topological surface states, indicating a robust and mode-selective coupling between the electronic states and various phonon modes. These experimental findings align with previous calculations of the Eliashberg function, providing a deeper understanding of the highest superconducting transition temperature observed in 2M-WS2 (8.8 K) among all transition metal dichalcogenides as induced by electron–phonon coupling. Furthermore, our results may offer valuable insights into other properties of 2M-WS2 and guide the search for high-temperature topological superconductors. Electron–phonon coupling is a key physical process in condensed matter systems that plays a crucial role in phenomena such as superconductivity. Here, the authors characterize the role of electron–phonon coupling in the topological superconductor candidate 2M-WS2, indicating a robust and mode-selective coupling that informs the nature of its relatively high superconducting transition temperature. [ABSTRACT FROM AUTHOR]

Highly-crystallized carbon nitride (HCCN) nanosheets exhibit significant potential for advancements in the field of photoelectric conversion. However, to fully exploit their potential, a thorough understanding of the fundamental excitonic photophysical processes is crucial. Here, the temperature-dependent excitonic photoluminescence (PL) of HCCN nanosheets and amorphous polymeric carbon nitride (PCN) is investigated using steady-state and time-resolved PL spectroscopy. The exciton binding energy of HCCN is determined to be 109.26 meV, lower than that of PCN (207.39 meV), which is attributed to the ordered stacking structure of HCCN with a weaker Coulomb interaction between electrons and holes. As the temperature increases, a noticeable reduction in PL lifetime is observed on both the HCCN and PCN, which is ascribed to the thermal activation of carrier trapping by the enhanced electron–phonon coupling effect. The thermal activation energy of HCCN is determined to be 102.9 meV, close to the value of PCN, due to their same band structures. Through wavelength-dependent PL dynamics analysis, we have identified the PL emission of HCCN as deriving from the transitions: σ *–LP, π *– π, and π *–LP, where the π *–LP transition dominants the emission because of the high excited state density of the LP state. These results demonstrate the impact of high-crystallinity on the excitonic emission of HCCN materials, thereby expanding their potential applications in the field of photoelectric conversion. [ABSTRACT FROM AUTHOR]

Here, we demonstrate a strategy for the quantification of electron–phonon interaction (EPI) of bismuth telluride (Bi2Te3) under hydrostatic pressure through systematic femtosecond pump-probe spectroscopy. Two optical phonon modes, namely A 1 g and Eg with frequencies of 1.87 and 3.71 THz at ambient pressure, are detected using time-resolved transient reflection (TR) measurement. Frequencies of both coherent phonon oscillations increase monotonically by around 33% and 17%, respectively, with the rising pressure up to 5.67 GPa, indicating pressure-induced phonon-hardening effect. The mode-specific electron–phonon coupling constant λ of Bi2Te3 under different pressures are calculated with the frequency of the A 1 g mode. It turns out that the variation of phonon lifetime and the corresponding phonon dephasing rate of the A 1 g mode may result from the pressure modification of λ. Our findings reveal the significant role of EPI in phonon transport and shed light on further manipulation on thermoelectric efficiency of Bi2Te3 with external strain. [ABSTRACT FROM AUTHOR]

Lead‐free perovskites exhibit unique crystal structures and optical properties due to their low‐dimensional structure. However, the 0D structure of Cs2InCl5·H2O usually demonstrates poor optical properties at room temperature due to their extremely strong electron–phonon coupling interaction. In this study, a doping strategy is employed by introducing Pb2+ into Cs2InCl5·H2O, resulting in the achievement of an efficient broadband blue emission, with a photoluminescence quantum yield (PLQY) of 58%. The temperature‐dependent PL spectra reveal that the efficient emission is attributed to the weakening of the electron–phonon coupling strength in the lattice and the inhibition of the phonon‐assisted non‐radiative recombination process through Pb2+ doping. The validity of this deduction is further corroborated by the results of the Raman spectra. The results of the first‐principle calculation demonstrate that the broadband emission originates from multiple emission paths in In3+ and Pb2+ polyhedrons. In addition, Pb2+‐doped Cs2InCl5·H2O can realize the transformation from sky‐blue emission to deep‐blue emission by absorbing water in the air. Remarkably, this change is reversible during the heating–cooling cycles, demonstrating excellent optical stability with repeatable recyclability. [ABSTRACT FROM AUTHOR]

Combining chirality with ferromagnetism is challenging in organic materials and may bring potential application for the cross-integration of multiple disciplines. In this work, we achieved the intrinsic coexistence of chirality and spontaneous spin polarization in the diblock copolymers, where left-handed and right-handed circularly polarized lights present tunability on both the circular dichroism and spin polarization. Without electron dependence of transport in chiral copolymer, chirality is still coupled with spin. The phenomenon observed here is not the traditional chirality induced spin selectivity effect. Moreover, the electric field could also effectively tune the chirality dependence of circular dichroism to further affect the magnitude of spin polarization. Thus, a strong relationship between the chirality and spin polarization is formed in chiral copolymers. In addition, because of the different molecular packing for chiral enantiomers, electron–phonon coupling strengths are different to lead to a difference in spin polarization. Overall, the properties of chirality, spontaneous spin polarization, and photon-chirality-spin coupling are developed and studied, which effectively promotes the ability of potential applications of chiral copolymers. [ABSTRACT FROM AUTHOR]

Polarons, which arise from the intricate interplay between excess electrons and/or holes and lattice vibrations (phonons), represent quasiparticles pivotal to the electronic behavior of materials. This review reaffirms the established classification of small and large polarons, emphasizing its relevance in the context of recent advances in understanding lead halide perovskites' behavior. The distinct characteristics of large and small polarons stem from the electron–phonon interaction range, which exerts a profound influence on materials' characteristics and functionalities. Concurrently, lead halides have emerged with exceptional opto‐electronic properties, featuring prolonged carrier lifetimes, low recombination rates, high defect tolerance, and moderate charge carrier mobilities; these characteristics make them a compelling contender for integration of optoelectronic devices. In this review, the formation of both small and large polarons within the lattice of lead halide perovskites, elucidating their role in protecting photogenerated charge carriers from recombination processes, is discussed. As optoelectronic devices continue to advance, this review underscores the importance of unraveling polaron dynamics to pave the way for innovative strategies for enhancing the performance of next‐generation photovoltaic technologies. Future research should explore novel polaronic effects using advanced computational and experimental techniques, enhancing our understanding and unlocking new applications in materials science and device engineering. [ABSTRACT FROM AUTHOR]

Highly efficient three-dimensional (3D) lead-free halide perovskites that produce blue light emission with outstanding stability have attracted global research attention. In order to increase the light emission efficiency of Rb2LiBiBr6 perovskites, band structure engineering can be performed by doping Cu2+ ions. In this work, the structural, chemical and optical characteristics of pure Rb2LiBiBr6 (RLBB) and Cu2+-doped Rb2LiBiBr6 (RLBBC) phosphors produced through conventional wet chemical processes are reported. A narrow and comparatively unique blue emission was exhibited by Cu2+-doped Rb2LiBiBr6 double perovskites (DPs) as a result of electron–phonon interactions. The phase purity and microstructure of the Rb2LiBiBr6:Cu2+ DP were assessed using X-ray diffraction and scanning electron microscopy, respectively. All the synthesized samples showed a orthorhombic crystal structure, and B sites had a substantial impact on the Pnma space group in the Rb2LiBiBr6 DP framework. The Bi3+ ions at the B′ sites were replaced by the doped Cu2+ ions, which distributed themselves to an equilibrium valence state and showed minimal variation in the ionic radius. Photoluminescence (PL) spectra were used to explore the corresponding mechanism of the Cu2+ → Bi3+ energy-transfer process. The Cu2+-doped Rb2LiBiBr6 (RLBBC) phosphors exhibited a blue emission at 469 nm when excited at 367 nm. It showed an optical bandgap of 2.87 eV at room temperature. This as-prepared perovskite showed outstanding stable chromaticity with (x,y) coordinate values of (0.1367, 0.0596) under a continuous irradiation of 367 nm UV light. This lead-free and highly effective Cu2+-Rb2LiBiBr6 DP has a wide range of applications in the rarest blue photonic and optoelectronic domains as it demonstrates the potential to overcome the obstacles of extreme toxicity and inadequate stability. [ABSTRACT FROM AUTHOR]

The quantum efficiency of AlGaN ultraviolet light-emitting diodes declines (droops) at increasing operating powers due to Auger–Meitner recombination (AMR). Using first-principles density-functional theory, we show that indirect AMR mediated by electron–phonon coupling and alloy disorder can induce bulk C coefficients as large as ∼ 10 − 31 cm6/s. Furthermore, we find that the confinement of carriers by polarization fields within quantum wells severely relaxes crystal-momentum conservation, which exacerbates the rate of AMR over radiative recombination by an order of magnitude relative to the bulk. This results in a striking decrease in quantum efficiency at high power. Suppressing polarization fields and jointly increasing the well width would greatly mitigate AMR and efficiency droop. [ABSTRACT FROM AUTHOR]

Electron–phonon coupling thermal resistance in metals is a key factor affecting the thermal boundary conductance (TBC) of metal–metal–dielectric systems. However, quantitatively differentiating the contribution of electron–phonon coupling to TBC is still a challenge, as various thermal resistances are coupled in a complicated manner at the metal–metal–dielectric interface. Herein, we propose a two-step strategy to study electron–phonon coupling. We first decouple the phonon–phonon thermal conductance (TBCp-p) between metallic interlayer and dielectric from the metal–metal–dielectric interface by experimentally characterizing the TBCp-p of a single metallic interlayer deposited dielectric with the transient thermoreflectance technique; Combining metal–metal–dielectric TBC measurement and a thermal circuit model with measured TBCp-p as input, the contribution of electron–phonon coupling to TBC of the metal–metal–dielectric system is differentiated quantitatively. For the Au–Ni–GaN system, the contribution of electron–phonon coupling thermal resistance in the Ni interlayer ( R e − p h , Ni ) is substantially higher at lower Ni interlayer thickness, reaching 35% at ∼1 nm Ni. The electron–phonon coupling constant of Ni (gNi) was fitted in the range of 6.4 × 1016–36 × 1016 W/m3K. The above results were also verified in the Au–Ni–SiC system. This study will promote a deeper understanding of the thermal transport in the metal–metal–dielectric system and provide an insightful indication for the manipulation of TBC in this system. [ABSTRACT FROM AUTHOR]

The concept of ferroelectricity is now often extended to include continuous inversion symmetry-breaking transitions in various metals and doped semiconductors. Paraelectric metals near ferroelectric quantum criticality, which we term 'quantum paraelectric metals,' possess soft transverse optical phonons which can have Rashba-type coupling to itinerant electrons in the presence of spin-orbit coupling. We find through the Kubo formula calculation that such Rashba electron-phonon coupling has a profound impact on electron spin transport. While the spin Hall effect arising from non-trivial electronic band structures has been studied extensively, we find here the presence of the Rashba electron-phonon coupling can give rise to spin current, including spin Hall current, in response to an inhomogeneous electric field even with a completely trivial band structure. Furthermore, this spin conductivity displays unconventional characteristics, such as quadrupolar symmetry associated with the wave vector of the electric field and a thermal activation behavior characterized by scaling laws dependent on the phonon frequency to temperature ratio. These findings shed light on exotic electronic transport phenomena originating from ferroelectric quantum criticality, highlighting the intricate interplay of charge and spin degrees of freedom. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Basrah Researches (Sciences) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With strong electron–phonon coupling, self‐trapped excitons (STEs) are typically formed in perovskite materials, and radiative recombination of STEs can produce broadband emission with large Stokes shifts. STEs are essential to further improve the optoelectronic properties of materials. Surprisingly, 2D system is the edge case, with low even no self‐trapping barriers, leading to effortless formation of STEs. In this work, 2D strontium titanate (SrTiO3) with defects is prepared using supercritical carbon dioxide (SC CO2) and its carrier transport and transition are studied. The appearance of wide photoinduced positive absorption signals in the femtosecond transient absorption spectra is direct evidence for the formation of STEs. The presence of STEs is further supported by the increased Stokes shift and full width at half maximum in the steady‐state photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo‐induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron‐phonon coupling via rational fluoro‐substitution. The optimized 2FBP‐4F catalyst we develop here exhibits a minimized Huang–Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP‐4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP‐4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6–561.8 mmol h−1 g−1) for hydrogen evolution than the control PM6 : BP‐4F and PM6 : 2FBP‐6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm−2). [ABSTRACT FROM AUTHOR]

We investigate emission characteristics, phonon–phonon, and electron–phonon interactions in a lead-free halide perovskite Cs 3 Sb 2 Br 9 through temperature-dependent photoluminescence, Raman scattering, and x-ray diffraction measurements. The exciton–optical phonon coupling leads to below bandgap broad emissions, arising from self-trapped excitons recombination. The anomalous temperature dependence of the lowest frequency Raman mode is attributed to the phonon–phonon and electron–phonon interactions. The temperature-dependent x-ray diffraction measurement reveals a minimum in the volume thermal expansion coefficient at around 120 K. We also quantify the quasiharmonic contributions to the phonon frequency shift for all Raman modes. [ABSTRACT FROM AUTHOR]

This paper investigates a wide‐band emitting red phosphor, an advancement that solves shortcomings including the re‐absorption of the yellow phosphor in the blue light area and a lack of red spectrum components which result in low color rendering and an uneven white light tone. An examination through femtosecond, Raman, and low‐temperature spectroscopy demonstrates why this phosphor has large Stokes shift (SS = 7.5×103 cm−1) and wide half‐peak width with a full‐width at half maximum (FWHM) of more than 170 nm. In these samples, it is importantly observed that larger lattice causes smaller electron–phonon coupling of Eu2+ activator, and meanwhile leads to less temperature dependency of emission peak width. The obtained sample, after cation replacement in (Ca1‐xSrx)7(SiO3)6Cl2: Eu2+ (CSSC: Eu2+), exhibits an emission spectrum covers the range from 450 to 800 nm while its excitation range is below 450 nm, in which not reabsorb the blue light. This matches well with blue phosphors that can also be excited by near‐ultraviolet chips. The fabricated white light‐emitting diode (w‐LED) device has an ideal color rendering index and correlated color temperature (Ra = 90.5, CCT = 3894 K), making it an excellent candidate material for white LED illumination. [ABSTRACT FROM AUTHOR]

This paper investigates a wide‐band emitting red phosphor, an advancement that solves shortcomings including the re‐absorption of the yellow phosphor in the blue light area and a lack of red spectrum components which result in low color rendering and an uneven white light tone. An examination through femtosecond, Raman, and low‐temperature spectroscopy demonstrates why this phosphor has large Stokes shift (SS = 7.5×103 cm−1) and wide half‐peak width with a full‐width at half maximum (FWHM) of more than 170 nm. In these samples, it is importantly observed that larger lattice causes smaller electron–phonon coupling of Eu2+ activator, and meanwhile leads to less temperature dependency of emission peak width. The obtained sample, after cation replacement in (Ca1‐xSrx)7(SiO3)6Cl2: Eu2+ (CSSC: Eu2+), exhibits an emission spectrum covers the range from 450 to 800 nm while its excitation range is below 450 nm, in which not reabsorb the blue light. This matches well with blue phosphors that can also be excited by near‐ultraviolet chips. The fabricated white light‐emitting diode (w‐LED) device has an ideal color rendering index and correlated color temperature (Ra = 90.5, CCT = 3894 K), making it an excellent candidate material for white LED illumination. [ABSTRACT FROM AUTHOR]

A series of lead-free Rb2ZrCl6:xTe4+ (x = 0%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 10.0%) perovskite materials were synthesized through a hydrothermal method in this work. The substitution of Te4+ for Zr in Rb2ZrCl6 was investigated to examine the effect of Te4+ doping on the spectral properties of Rb2ZrCl6 and its potential applications. The incorporation of Te4+ induced yellow emission of triplet self-trapped emission (STE). Different luminescence wavelengths were regulated by Te4+ concentration and excitation wavelength, and under a low concentration of Te4+ doping (x ≤ 0.1%), different types of host STE emission and Te4+ triplet state emission could be achieved through various excitation energies. These luminescent properties made it suitable for applications in information encryption. When Te4+ was doped at high concentrations (x ≥ 1%), yellow triplet state emission of Te4+ predominated, resulting in intense yellow emission, which stemmed from strong exciton binding energy and intense electron-phonon coupling. In addition, a Rb2ZrCl6:2%Te4+@RTV scintillating film was fabricated and a spatial resolution of 3.7 lp/mm was achieved, demonstrating the potential applications of Rb2ZrCl6:xTe4+ in nondestructive detection and bioimaging. [ABSTRACT FROM AUTHOR]

Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron–phonon coupling, the dynamics of the organic cations, and the degree of lattice distortion. We report temperature-dependent Raman studies of BA2MAPb2I7 and BA2MA2Pb3I10 (BA = butylammonium; MA = methylammonium), which undergo two structural phase transitions. Raman data obtained in broad temperature (360–80 K) and wavenumber (1800–10 cm−1) ranges show that ordering of BA+ cations triggers the higher temperature phase transition, whereas freezing of MA+ dynamics occurs below 200 K, leading to the onset of the low-temperature phase transition. This ordering is associated with significant deformation of the inorganic sublattice, as evidenced by changes observed in the lattice mode region. Our results show, therefore, that Raman spectroscopy is a very valuable tool for monitoring the separate dynamics of different organic cations in perovskites, comprising "perovskitizer" and interlayer cations. [ABSTRACT FROM AUTHOR]

The superconductivity of CaC6 as a function of pressure and Ca isotopic composition was revisited using DFT calculations on a 2c–double hexagonal superlattice. The introduction of superlattices was motivated by previous synchrotron absorption and Raman spectroscopy results on other superconductors that showed evidence of superlattice vibrations at low (THz) frequencies. For CaC6, superlattices have previously been invoked to explain the ARPES data. A superlattice along the hexagonal c-axis direction is also illustrative of atomic orbital symmetry and periodicity, including bonding and antibonding s-orbital character implied by cosine-modulated electronic bands. Inspection of the cosine band revealed that the cosine function has a small (meV) energy difference between the bonding and antibonding regions, relative to a midpoint non-bonding energy. Fermi surface nesting was apparent in an appropriately folded Fermi surface using a superlattice construct. Nesting relationships identified phonon vectors for the conservation of energy and for phase coherency between coupled electrons at opposite sides of the Fermi surface. A detailed analysis of this Fermi surface nesting provided accurate estimates of the superconducting gaps for CaC6 with the change in applied pressure. The recognition of superlattices within a rhombohedral or hexagonal representation provides consistent mechanistic insight on superconductivity and electron−phonon coupling in CaC6. [ABSTRACT FROM AUTHOR]

Quantum magneto-transport in a dissipative single molecular transistor is investigated at finite temperature in the presence of electron correlation and electron–phonon interaction within the framework of the Anderson–Holstein–Caldeira–Leggett Hamiltonian. The electron–phonon interaction and dissipation are dealt with by canonical transformations and the Coulomb correlation is treated at the mean-field level. The transport properties such as spectral function, tunneling current, differential conductance, and spin polarization are determined using the Keldysh method. [ABSTRACT FROM AUTHOR]

We employ quasiparticle path integral molecular dynamics to study how the excitonic properties of model semiconductors are altered by electron–phonon coupling. We describe ways within a path integral representation of the system to evaluate the renormalized mass, binding energy, and radiative recombination rate of excitons in the presence of a fluctuating lattice. To illustrate this approach, we consider Fröhlich-type electron–phonon interactions and employ an imaginary time influence functional to incorporate phonon-induced effects nonperturbatively. The effective mass and binding energies are compared with perturbative and variational approaches, which provide qualitatively consistent trends. We evaluate electron-hole recombination rates as mediated through both trap-assisted and bimolecular processes, developing a consistent statistical mechanical approach valid in the reaction limited regime. These calculations demonstrate how phonons screen electron–hole interactions, generically reducing exciton binding energies and increasing their radiative lifetimes. [ABSTRACT FROM AUTHOR]

Thanks to their formidable electron transport properties, III–V compound semiconductors have established themselves as a possible alternative to strained-Si as future n-type logic switches. To predict the performance of such transistors, device simulators that can capture the peculiarities of the III–V band structure at low computational cost are required. In particular, their strong band non-parabolicity (NP) calls for advanced models going beyond the standard effective mass approximation (EMA). Previous studies have suggested ways to include NP effects into quantum transport calculations in the ballistic limit. Here, such a model is extended to account for electron–phonon interactions. It combines the non-equilibrium Green's function formalism and the EMA with NP corrections. The proposed method is validated through simulations of InGaAs nanowire field-effect transistors. The results are compared to full-band tight-binding calculations and to the solution of the subband Boltzmann transport equation, showing excellent agreement. [ABSTRACT FROM AUTHOR]

In the present work, the effect of all-round compression up to 10 kbar on the in-plane electrical resistivity of well-structured Y0.66Pr0.34Ba2Cu3O7–δ (δ < 0.15, Тс ≈ 51.8 K, ΔТс ≈ 2 K) single crystals has been investigated. In contrast to the samples with low praseodymium doping (x ≈ 0.05), the application of all-round compression to the samples with medium praseodymium doping (х ≈ 0.34) leads to an increase in the baric derivative dТс/dP by more than two times. It was found that, in contrast to polycrystalline samples, there was no change in the sign of the baric derivatives dТс/dP. The applicability of the well-known McMillan formula to explain the effect of all-round compression on Тс is discussed. [ABSTRACT FROM AUTHOR]

Polar optical phonon modes of wurtzite triangular nanowires (NWs) with three different cross sections, including the hemi-equilateral triangle (HET), the isosceles right triangle (IRT), and the equilateral triangle (ET), are deduced and analyzed using the dielectric continuum model. The exact and analytical phonon states of exactly confined (EC) modes in nitride NWs with HET, IRT, and ET cross sections are derived. The characteristic frequency of EC phonon modes in the triangular nitride NW systems is specified. Fröhlich electron–phonon interaction Hamiltonians in wurtzite NWs with three types of triangular cross sections are obtained. It is found from the numerical results that, among the three types of GaN NWs, the electron–phonon coupling of EC modes in NWs with an HET cross section is the weakest one, that in NWs with an ET cross section is the strongest one, and that in NWs with an IRT cross section is in the middle. The electrostatic potentials of EC modes in HET NWs are neither symmetric nor antisymmetric. The potential functions of EC modes in the ET NW structures have one (three) symmetric axis (axes) as the quantum numbers p and q take fractions (integers). The potential functions of EC modes in IRT NWs behave either symmetrically or anti-symmetrically, which are closely dependent on the parities of the quantum numbers p and q. With the increase of order-number of EC modes, the electron–phonon coupling becomes weaker and weaker. This reveals that cross-sectional morphology of quantum structures has an important influence on the symmetries of phonon modes and electron–phonon coupling strengths in low-dimensional quantum systems. [ABSTRACT FROM AUTHOR]

A new diagrammatic quantum Monte Carlo approach is proposed to deal with the imaginary time propagator involving both dynamic disorder (i.e., electron–phonon interactions) and static disorder of local or nonlocal nature in a unified and numerically exact way. The establishment of the whole framework relies on a general reciprocal-space expression and a generalized Wick's theorem for the static disorder. Since the numerical cost is independent of the system size, various physical quantities, such as the thermally averaged coherence, Matsubara one-particle Green's function, and current autocorrelation function, can be efficiently evaluated in the thermodynamic limit (infinite in the system size). The validity and performance of the proposed approach are systematically examined in a broad parameter regime. This approach, combined with proper numerical analytic continuation methods and first-principles calculations, is expected to be a versatile tool toward the calculation of various transport properties, such as mobilities in realistic semiconductors involving multiple electronic energy bands, high-frequency optical and low-frequency acoustic phonons, different forms of dynamic and static disorders, and anisotropy. [ABSTRACT FROM AUTHOR]

Janus transition metal dichalcogenides with out-of-plane structural asymmetry have attracted increasing attention due to their exceptional potential in electronic and optical applications. In this study, we systematically investigated the electron–phonon interactions and related transport properties in monolayer Janus MoSSe and WSSe using the density-functional formalism. The electron–phonon scattering rates were obtained using Fermi's golden rule and extended to the extraction of the effective deformation potential constants for further Monte Carlo treatment. From the results of the Monte Carlo analysis, we found that WSSe provides better performance with higher low-field mobility, while MoSSe shows a higher peak velocity at higher fields. In our results, both MoSSe and WSSe seem to be competitive with other previously studied 2D materials. These predictions provide a systematic perspective on the potential of Janus WSSe and MoSSe for electronic applications. [ABSTRACT FROM AUTHOR]

The electronic, phonon, and superconducting properties of hexagonal yttrium hydrogen selenide (YHSe) are studied using density functional theory (DFT) methods. The DFT analysis revealed that the energy bandgap and density of states near the Fermi energy (ɛF) decrease with increasing pressure. Additionally, the influence of pressure on the vibrational properties of YHSe is also examined. The findings of the vibrational properties indicate a stiffening of lattice dynamics under pressure and the identification of negative Gruneisen parameters at certain high symmetry sites. This enhances and deepens the understanding of the vibrational characteristics of YHSe under extreme pressure conditions. Finally, the electron–phonon coupling (EPC) parameter (λ) is examined under different pressures. The examination of EPCs across varying pressures showed a significant increase from 0.826 (0 GPa) to 2.6287 (200 GPa), where an increase in this EPC is found to increase the superconducting critical temperature (Tc). Furthermore, the nonmonotonic relationship between the superconducting critical temperature (Tc) and external pressure (P) in the YHSe compound is observed. Initially, Tc decreases with increasing pressure and then begins to rise again, reaching its peak value at extreme pressure. These findings provide valuable insights into the pressure-dependent properties of YHSe and have important implications for the field of superconductivity in condensed matter physics. [ABSTRACT FROM AUTHOR]

High open‐circuit voltage (Voc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non‐fused ring electron acceptors (NFREAs), HF‐BTA33 and HCl‐BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron‐phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF‐BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a Voc of 1.232 V, higher than that of symmetric analogue F‐BTA33 (PCE=10.02 %, Voc=1.197 V). Notably, PTQ10 : HCl‐BTA33 achieves the highest PCE of 12.54 % with a Voc of 1.201 V due to the long‐range ordered π–π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and Voc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs. [ABSTRACT FROM AUTHOR]

In this work, we investigate collective electronic fluctuations and, in particular, the possibility of the charge density wave ordering in an infinite-layer NdNiO2. We perform advanced many-body calculations for the ab-initio three-orbital model by taking into account local correlation effects, nonlocal charge and magnetic fluctuations, and the electron-phonon coupling. We find that in the considered material, electronic correlations are strongly orbital- and momentum-dependent. Notably, the charge density wave and magnetic instabilities originate from distinct orbitals. In particular, we show that the correlation effects lead to the momentum-dependent hybridization between different orbitals, resulting in the splitting and shifting of the flat part of the Ni- d z 2 band. This strong renormalization of the electronic spectral function drives the charge density wave instability that is related to the intraband Ni- d z 2 correlations. Instead, the magnetic instability stems from the Ni- d x 2 − y 2 orbital, which remains half-filled through the redistribution of the electronic density between different bands even upon hole doping. Consequently, the strength of the magnetic fluctuations remains nearly unchanged for the considered doping levels. We argue that this renormalization is not inherent to the stoichiometric case but can be induced by hole doping. [ABSTRACT FROM AUTHOR]

Halide perovskites emerged as a revolutionary family of high-quality semiconductors for solar energy harvesting and energy-efficient lighting. There is mounting evidence that the exceptional optoelectronic properties of these materials could stem from unconventional electron-phonon couplings, and it has been suggested that the formation of polarons and self-trapped excitons could be key to understanding such properties. By performing first-principles simulations across the length scales, here we show that halide perovskites harbor a uniquely rich variety of polaronic species, including small polarons, large polarons, and charge density waves, and we explain a variety of experimental observations. We find that these emergent quasiparticles support topologically nontrivial phonon fields with quantized topological charge, making them nonmagnetic analog of the helical Bloch points found in magnetic skyrmion lattices. [ABSTRACT FROM AUTHOR]

We report the temperature dependences of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of the uniaxial crystal GaSe in the spectral energy region from 0.74 to 6.42 eV and at temperatures from 27 to 300 K using spectroscopic ellipsometry. The fundamental bandgap and strong exciton effect near 2.1 eV are detected only in the c-direction, which is perpendicular to the cleavage plane of the crystal. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that incorporates the Bose–Einstein statistical factor and the temperature coefficient to describe the electron–phonon interaction. To determine the origin of this anisotropy, we perform first-principles calculations using the mBJ method for bandgap correction. The results clearly demonstrate that the anisotropic dielectric characteristics can be directly attributed to the inherent anisotropy of p orbitals. More specifically, this prominent excitonic feature and fundamental bandgap are derived from the band-to-band transition between s and pz orbitals at the Γ-point. [ABSTRACT FROM AUTHOR]

Dirac materials, due to their unique physical properties, hold vast prospects in both fundamental research and practical applications. Recently, the metallic Dirac material, molybdenene, has been synthesized. However, free-standing molybdenene is found to be dynamically unstable. We propose the use of F/Li to modify its structure and stabilize it. Based on density functional theory, density functional perturbation theory, and anisotropic Migdal–Eliashberg equations, we systematically investigate the electronic structures and superconducting properties of MoF and MoLi. The results indicate that both MoF and MoLi are intrinsic superconductors, with electron–phonon coupling constants of 0.49 and 0.74, respectively. Solving the superconducting gap equation yields a superconducting transition temperature of 7.5 K for MoLi. Further analysis suggests that the coupling between the out-of-plane component of Mo's d orbital electrons and the vibrations of Mo atoms contributes significantly to the electron–phonon coupling in MoLi. Our study lays the foundation for further applications of molybdenene. [ABSTRACT FROM AUTHOR]

Aluminum scandium alloys and their intermetallic phases have arisen as potential candidates for the next generation of electrical interconnects. In this work, we measure the in-plane thermal conductivity and electron–phonon coupling factor of aluminum scandium alloy thin films deposited at different temperatures, where the temperature is used to control the grain size and volume fraction of the Al3Sc intermetallic phase. As the Al3Sc intermetallic formation increases with higher deposition temperature, we measure increasing in-plane thermal conductivity and a decrease in the electron–phonon coupling factor, which corresponds to an increase in grain size. Our findings demonstrate the role that chemical ordering from the formation of the intermetallic phase has on thermal transport. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid Ge(II)‐based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics. However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application. In addressing these issues, a breakthrough in the large‐scale production of Sb3+‐doped Ge(IV)‐based metal halide (C13H14N3)2GeCl6 phosphors at room temperature through a straightforward solution method is presented. The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 ± 0.06% the highest among Ge(IV)‐based metal halides. Notably, the introduction of Sb3+ induces the formation of Jahn–Teller‐like self‐trapped excitons in [SbCl6]3− species, attributable to lattice distortion and strong electron–phonon coupling. Consequently, Sb3+‐doped (C13H14N3)2GeCl6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs). Furthermore, the Sb3+‐doped compound exhibits commendable chemical‐ and photostability, prompting exploration in applications such as white light‐emitting diodes and latent fingerprint detection. This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application. [ABSTRACT FROM AUTHOR]

[Display omitted] Electron–phonon interactions and electron–electron correlations represent two crucial facets of condensed matter physics. For instance, in a half-filled spin-1/2 anti-ferromagnetic chain, the lattice dimerization induced by electron-nucleus interaction can be intensified by onsite Coulomb repulsion, resulting in a spin-Peierls state. Through first-principles calculations and crystal structure prediction methods, we have identified that under mild pressures, potassium and ammonia can form stable compounds: R 3 ¯ m K(NH 3) 2 , Pm 3 ¯ m K(NH 3) 2 , and Cm K 2 (NH 3) 3. Our predictions suggest that the R 3 ¯ m K(NH 3) 2 exhibits electride characteristics, marked by the formation of interstitial anionic electrons (IAEs) in the interlayer space. These IAEs are arranged in quasi-two-dimensional triangular arrays. With increasing pressure, the electronic van-Hove singularity shifts toward the Fermi level, resulting in an augmented density of states and the onset of both Peierls and magnetic instabilities. Analyzing these instabilities, we determine that the ground state of the R 3 ¯ m K(NH 3) 2 is the dimerized P 2 1 / m phase with zigzag-type anti-ferromagnetic IAEs. This state can be described by the triangular-lattice antiferromagnetic Heisenberg model with modulated magnetic interactions. Furthermore, we unveil the coexistence and positive interplay between magnetic and Peierls instability, constituting a scenario of spin-Peierls instability unprecedented in realistic 2D materials, particularly involving IAEs. This work provides valuable insights into the coupling of IAEs with the adjacent lattice and their spin correlations in quantum materials. [ABSTRACT FROM AUTHOR]

Structural mosaic of rare-earth tri-tellurides (RTe3) inlaid with non-classical structural motifs like the 2D-polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe3, an archetypal RTe3, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets … between the charged double corrugated slabs of n[GdTe]+. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe3 across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe3 engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd-Te slab and Te square net, and the robust electron-phonon coupling. [ABSTRACT FROM AUTHOR]

Highlights: The soft 2D material reduces the coupling strength between carriers and longitudinal optical phonons, releasing the mechanical stress of lattice vibration. The power conversion efficiency of rigid devices and flexible devices reaches 25.5% and 23.4%, respectively. This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron–phonon coupling of perovskite in perovskite solar cells (PSCs). Via A-site cation engineering, a weaker electron–phonon coupling in perovskite has been achieved by introducing the structurally soft cyclohexane methylamine (CMA+) cation, which could serve as a damper to alleviate the mechanical stress caused by lattice oscillations, compared to the rigid phenethyl methylamine (PEA+) analog. It demonstrates a significantly lower non-radiative recombination rate, even though the two types of bulky cations have similar chemical passivation effects on perovskite, which might be explained by the suppressed carrier capture process and improved lattice geometry relaxation. The resulting PSCs achieve an exceptional power conversion efficiency (PCE) of 25.5% with a record-high open-circuit voltage (VOC) of 1.20 V for narrow bandgap perovskite (FAPbI3). The established correlations between electron–phonon coupling and non-radiative decay provide design and screening criteria for more effective passivators for highly efficient PSCs approaching the Shockley–Queisser limit. [ABSTRACT FROM AUTHOR]

Structural mosaic of rare-earth tri-tellurides (RTe3) inlaid with non-classical structural motifs like the 2D-polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe3, an archetypal RTe3, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets … between the charged double corrugated slabs of n[GdTe]+. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe3 across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe3 engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd-Te slab and Te square net, and the robust electron-phonon coupling. [ABSTRACT FROM AUTHOR]