Asymmetric Doublet Research Articles

Temperature-Dependent Photoluminescence from Well-Resolved Excited State Structures in Rare-Earth-Based Double Perovskites.

Lead-free halide double perovskites (DPs) have become a research hotspot in the field of photoelectrons due to their unique optical properties and flexible compositional tuning. However, the reports on the optical properties of DPs primarily concentrate on the room temperature state and only exhibit single emission band. Here, we synthesized Cs2NaYCl6:Sb3+, Dy3+ DPs by a solvothermal method to realize white light emission with photoluminescence (PL) quantum yield as high as 70.7%. The energy-transfer process from self-trapped excitons (STEs) to Dy3+ ions was revealed by optical characterization and theoretical simulation calculations. Interestingly, we observed the double-emission from low-energy STE emission of Sb3+ ions and Dy3+ emission at low temperatures, and the double-emission is consistent with the asymmetric doublet feature of the 3P1 → 1S0 transition split into two minima. The PL spectra further showed that the fluorescence intensity ratios of Dy3+ ions at 580 and 680 nm were strongly temperature-dependent, and the relative sensitivity is up to 1.79% K-1 at 360 K. Moreover, the near-infrared and radiation luminescence properties indicated that the Cs2NaYCl6:Sb3+, Dy3+ DPs also have good prospects for night vision and radiation detection, as well as the great potential for applications in solid-state illumination and optical temperature measurement.

Phase Separation in the Double Perovskite Sr2FeNbO6-δ

The ceramic perovskite Sr2FeNbO6-δ was synthesized via the solution combustion precursor method. X-ray phase analysis showed that the sample is single-phase and does not contain impurities. The specific heat capacity and the Mössbauer spectra were measured for the Sr2FeNbO6-δ ceramic in the temperature range of 4–300 K. The observation of an asymmetric doublet in the Mössbauer spectra and the literature data on the magnetic susceptibility indicated the presence of two magnetic subsystems in Sr2FeNbO6-δ with antiferromagnetic exchange interactions. Based on the analysis of the temperature dependence of the specific heat capacity, we determined the Debye and Einstein temperatures.

Numerical modeling of low-frequency distributed acoustic sensing signals for mixed-mode reactivation

In recent years, the development of distributed acoustic sensing (DAS) technology has enabled direct monitoring of subsurface strain during hydraulic fracturing (HF) operations. Most low-frequency (<1 Hz) DAS (LFDAS) signals exhibit strain or strain-rate patterns that are characteristic of propagating tensile hydraulic fractures. However, mixed-mode fault reactivation, consisting of shear slip (mode II) with tensile opening (mode I), can occur in cases where propagating hydraulic fractures intersect preexisting natural fractures or faults. In this study, we show an anomalous LFDAS signal that was observed during an HF operation, with characteristics that differ from typical signals from tensile hydraulic fractures. Anomalous characteristics include the onset of an asymmetric compression-extension doublet after pumping was terminated. The location of the signals, coupled with the image log and seismic data, suggests that mixed-mode reactivation occurred on a preexisting fault. We use a simplified numerical model based on the displacement discontinuity method (DDM) to simulate the anomalous LFDAS signal. Results find that the first-order characteristics of the anomalous signal can be approximated as an initial tensile fault opening (mode I) followed by a shear slip (mode II) on a fault. Therefore, we demostrate the approach of using DDM to investigate mixed-mode fault reactivation during HF operations.

The specificity of photoluminescence n-CdS/p-CdTe in semiconductor heterostructures

The low-temperature (4.2 K) near-band-edge photoluminescence spectrum of a thin fine-grained (h, dcr≤1μm) polycrystalline CdTe layer in an n-CdS/p-CdTe film heterostructure subjected to frontal excitation by an Ar+ laser with an intensity of ~44 W/cm2 consists of a dominant intrinsic (e-h) emission band with a half-width ΔA=10-12 meV and a blue shift ΔEr » 25 meV of the red edge with respect to Eg, its LO+nLA phonon replica (ΔB»40 meV) with a weak doublet structure, and a wide (ΔD»100 meV) surface-interface luminescence band peaking at a frequency ħω»1.49 eV. Rear-side illumination of the photoresistive CdS layer in the intrinsic absorption range with an intensity Lill ≈ 5.102 lx almost completely destroys the e-hband and all related luminescence lines, which are replaced with an asymmetric polariton emission doublet having an exciton resonance frequency ħω»1.59 eV(Δex» 25 meV) and a wide line of shallow donor–acceptor pairs (ΔDAP»40 meV) at a frequency of ħω»1.54 eV, whose maximum intensity is almost two orders of magnitude lower than that of the A line in the absence of illumination.

Hard x-ray photoemission spectroscopy of the ferrimagnetic series Gd6(Mn1−xFex)23

We study the evolution of the electronic structure of the intermetallic series ${\mathrm{Gd}}_{6}{({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})}_{23}, x=0.0--0.75$, which shows nonmonotonic ferrimagnetic ordering temperatures ${T}_{C}$ but with a systematic reduction of the total bulk magnetization upon increasing Fe content, $x$. We have carried out hard x-ray photoemission spectroscopy to elucidate the relation between electronic structure and properties of the series. The Gd $3d$ and Gd $4d$ core-level spectra indicate trivalent ${\mathrm{Gd}}^{3+}$ multiplets in the intermediate-coupling scheme with features due to $L\text{\ensuremath{-}}S$ and $j\text{\ensuremath{-}}J$ coupling. The Fe $2p$ core levels show asymmetric single peak metal-like spectra, while the Mn $2p$ core levels show asymmetric doublet peaks. The relative intensities of the Mn $2p$ doublets as a function of $x$ indicate occupancy changes of distinct crystallographic sites associated with Mn up-spin and down-spin states. The valence band spectra identify the Gd $4f$ states at high binding energies ($\ensuremath{\sim}7.4$ eV). The Mn $3d$ states occur at the Fermi level and as a broad feature between 2 and 5 eV binding energy in ${\mathrm{Gd}}_{6}{\mathrm{Mn}}_{23}$. Upon substitution, the Fe $3d$ states show up as small shifts to higher binding energies compared to Mn $3d$ states. The Fe $3s$ and Mn $3s$ spectra show exchange split peaks, allowing an estimate of the Mn and Fe magnetic moments using a Van Vleck analysis, which also provides a quantification of occupancy changes with $x$. The overall results are consistent with the bulk net magnetization, indicating that Mn up-spin sites become Fe down-spin sites on substitution, while the nonmonotonic ${T}_{C}$ originates in a change from Mn sublattice to Fe sublattice derived ordering.

Physical properties of nanosized (x)NiO/(1−x)CdFe2O4 composites

This study investigates the optical and magnetic properties of nanosized (x)NiO/(1−x)CdFe2O4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 1) composites. The samples were synthesized using the wet coprecipitation technique. The X-ray Diffraction patterns demonstrated the formation of Nickel Oxide (NiO) and Cadmium Ferrite (CdFe2O4) phases without any chemical reaction between them. Fourier Transform Infrared results confirm the formation of pure NiO, pure CdFe2O4, and nanosized NiO/CdFe2O4 composites. Transmission Electron Microscopy micrographs show agglomeration between the nanoparticles, demonstrating the magnetic interaction between the oxide and ferrite phases. High-Resolution Transmission Electron Microscopy results verify the presence of NiO and CdFe2O4 phases in each nanosized composite without impurities, which is consistent with the XRD data. The ultraviolet–visible spectroscopy results confirmed that HCl is a better solvent than ethanol in investigating the optical properties of nanosized oxide/ferrite composites. Photoluminescence spectra exhibited asymmetricity owing to the presence of various emission peaks, which reveals the distribution of defect states within the bandgap of the nanosized composites. The Mössbauer spectra of the nanosized composites comprised an asymmetrical doublet at 300 K and an asymmetrical centered doublet within minor sextets at 77 K. Vibrating Sample Magnetometer study showed a shift at 77 K, which can be attributed to the spontaneous exchange bias effect. The magnetic parameters extracted from the M − H loops of all the synthesized nanosized composites at 77 K are higher than those at 300 K.

Dielectric properties, Mössbauer study, ESR spectra of Bi2FeTa2O9.5 with pyrochlore structure

The pyrochlore with the composition Bi2FeTa2O9.5 was obtained by solid-phase synthesis. The electronic state and the nature of the local environment of iron atoms were studied by electron spin resonance (ESR) and Mössbauer spectroscopy. In the Bi2FeTa2O9.5 ESR spectra a dipolar-broadened line with g ∼ 2.05 from Fe3+ ion clusters are observed. This line is the superposition of components with widths of about 150 and 400 mT. On the low-field wing of the band, there is a feature with g ∼ 4.3 relating to trace amounts of isolated Fe3+ ions in an octahedral position with a strong rhombic distortion. The Mössbauer spectrum of the Bi2FeTa2O9.5 compound demonstrates a slightly asymmetric doublet. The form of the doublet is reproduced by a superposition of a doublet and a singlet. About 93% of the spectral area of the paramagnetic part of the spectrum falls on the Fe(III)-doublet with IS = 0.365 ± 0.0020 mm/s, QS = 0.604 ± 0.034 mm/s, correlated with Fe3+ ions in regular axial octahedral positions. The remaining part is represented by a Fe(III)-singlet with IS = 0.176 ± 0.0288 mm/s from Fe3+ ions in a symmetric environment. The electrical properties of the compound were studied at temperatures of 20 – 450 °C in the frequency range of 25 Hz – 1 MHz. It was found that synthesized ceramics exhibit dielectric properties. The permittivity and the dielectric loss tangent at 20 °C were determined and are 57 and 0.003 (1 MHz), respectively.

Analytical Method for the Bending Resistance of Slim Floor Beams with Asymmetric Double-T Steel Section under ISO Fire

The slim floor beams, characterized by the steel profile embedded in the concrete slab, may be found in different configurations, based on the shape of the steel profile cross-section, which can vary from a rectangular to double-T section. While the most common shape used nowadays is the double-T cross-section, the Eurocodes do not provide a simplified method for the fire resistance assessment. The literature offers a simplified method for computation of bending resistance under elevated temperature, based on existing research on thermal models, and was validated for a particular type of slim floor beams (SFB). The current study extends the scope of application of this method, for different types of slim floor beam, which include an asymmetric double-T steel cross-section. The objective was reached through a numerical procedure, by analyzing 162 configurations subjected to four different fire requirements (R30, R60, R90, R120), resulting in a total of 648 analyses, performed with a validated numerical model in SAFIR software. The results in terms of bending resistance showed that the simplified method represents a strong tool for the fire design of slim floor beams.

Cosmological Evolution of a Statistical System of Degenerate Scalarly Charged Fermions with an Asymmetric Scalar Doublet. I. Two-Component System of Assorted Charges

Based on the mathematical model of a statistical system with scalar interaction of fermions formulated earlier, a cosmological model based on a two-component statistical system of scalar charged degenerate fermions interacting with an asymmetric scalar doublet, canonical and phantom scalar fields, is investigated. The asymptotic and limiting properties of the cosmological model are investigated, and it is shown that among all models there is a class of models with a finite lifetime. The asymptotic behavior of models near the corresponding singularities is investigated and numerical implementations of such models are constructed.

Cosmological models based on a statistical system of scalar charged degenerate fermions and an asymmetric Higgs scalar doublet

On the basis of the general relativistic statistical and kinetic theory, a consistent closed cosmological model is formulated. It is based on a statistical system of scalar charged fermions interacting by means of classical and phantom scalar fields. Based on the study of the microscopic dynamics of scalar charged particles, within the framework of the Lagrangian as well as Hamiltonian formalism, a function of the dynamic mass of scalar charged particles was constructed and it was shown that for the consistency of the theory, it is necessary to remove the nonnegativity condition for this function. On the basis of the Lagrangian formalism, equations of gravitational and scalar fields with singular sources are formulated and microscopic conservation laws are obtained. Within the framework of the general relativistic kinetic theory, macroscopic equations of gravitational and scalar fields are formulated and macroscopic conservation laws are obtained. These equations' full correspondence to microscopic equations with singular sources is shown. Further, on the basis of the obtained equations, a cosmological model for a degenerate system of scalarly charged fermions is formulated. An exact solution of the constitutive equations for a degenerate scalar-charged plasma in the cosmological model is obtained, which made it possible to significantly simplify the original system of equations. On the basis of the obtained solution of the constitutive equations, two fundamentally different cosmological models are formulated, one of which has two types of singly scalarly charged fermions, while the second has one kind of fermions charged with two charges of various nature. A qualitative analysis of the obtained 6-dimensional dynamic system for a two-component model is carried out.

Cosmological models based on a statistical system of scalar charged degenerate fermions and an asymmetric Higgs scalar doublet

На основе общерелятивистской статистической и кинетической теории сформулирована непротиворечивая замкнутая космологическая модель, основанная на статистической системе скалярно заряженных фермионов, взаимодействующих посредством классических и фантомных скалярных полей. На основе исследования микроскопической динамики скалярно заряженных частиц в рамках как лагранжева, так и гамильтонова формализма построена функция динамической массы скалярно заряженных частиц и показано, что для непротиворечивости теории необходимо снятие условия неотрицательности этой функции. На основе лагранжева формализма сформулированы уравнения гравитационных и скалярных полей с сингулярными источниками и получены микроскопические законы сохранения. В рамках общерелятивистской кинетической теории сформулированы макроскопические уравнения гравитационных и скалярных полей и показано их полное соответствие микроскопическим уравнениям с сингулярными источниками, а также получены макроскопические законы сохранения. На основе полученных уравнений сформулирована космологическая модель для вырожденной системы скалярно заряженных фермионов. Получено точное решение материальных уравнений для вырожденной скалярно заряженной плазмы в космологической модели, что позволило существенно упростить исходную систему уравнений. На основе полученного решения материальных уравнений сформулированы две принципиально различные космологические модели, в одной из которых имеются два сорта однократно скалярно заряженных фермионов, а во второй - один сорт фермионов, заряженных двумя зарядами различной природы. Проведен качественный анализ полученной шестимерной динамической системы для двухкомпонентной модели. Показано, что в таких моделях становятся возможными режимы торможения и ускорения на поздних стадиях эволюции Вселенной.

Complete cosmological model based on an asymmetric scalar Higgs doublet

A study of a complete cosmological model based on an asymmetric scalar doublet represented by the classical and phantom scalar Higgs fields is carried out. At the same time, the assumption about the nonnegativity of the expansion rate of the Universe, which in some cases contradicts the complete system of Einstein's equations, was removed. A closed system of dynamic equations describing the evolution of the cosmological model is formulated, and the dependence of the topology of the Einstein - Higgs hypersurface of the 5-dimensional phase space of the dynamical system that determines the global properties of the cosmological model on the fundamental constants of the model is investigated. A qualitative analysis of the dynamical system of the corresponding cosmological model is carried out, asymptotic phase trajectories are constructed, and the results of numerical modeling are presented, illustrating various types of behavior of the cosmological model.

Complete cosmological model based on an asymmetric scalar Higgs doublet

Проведено исследование полной космологической модели, основанной на асимметричном скалярном дублете, представленном классическим и фантомным скалярными полями Хиггса. При этом снято предположение о неотрицательности скорости расширения Вселенной, противоречащее в ряде случаев полной системе уравнений Эйнштейна. Сформулирована замкнутая система динамических уравнений, описывающих эволюцию космологической модели, исследована зависимость топологии гиперповерхности Эйнштейна-Хиггса пятимерного фазового пространства динамической системы, определяющей глобальные свойства космологической модели, от фундаментальных констант модели. Проведен качественный анализ динамической системы соответствующей космологической модели, построены фазовые траектории, иллюстрирующие различные типы поведения космологической модели. Выявлены типы поведения космологической модели, соответствующие переходам между фазами космологического сжатия и расширения.

Dark Lock-in Thermography Identifies Solder Bond Failure as the Root Cause of Series Resistance Increase in Fielded Solar Modules

Correlating the electrical performance of photovoltaic modules to the spatially resolved photoluminescence, electroluminescence, and dark lock-in thermography (DLIT) images is an important long-term goal for developing solar cell technology. These images offer highly sophisticated and detailed information about the spatial distribution and (if imaged at successive time intervals) temporal degradation of local series and shunt resistances. There have been extensive studies to correlate these imaging techniques to local characteristics at the cell level. However, it has been difficult to extract and quantify module-level information from the techniques. In this study, we interpret module current-voltage (I-V) measurements along with corresponding DLIT images within a module-scale simulation framework, demonstrating that series resistance degradation of the module I-V characteristics, in this case, can be attributed to solder bond failures. Our simulations highlight how current crowding associated with a failed solder joint (or a section of the solder pad) translates to the characteristic point-like (asymmetric doublet) heating pattern in neighboring solder joints (or the neighboring regions of the solder pad). The correlation between series resistance and solder joint degradation could inform expedited diagnosis of field degradation of solar modules.

Physical Characteristics of Free Oscillations of Scalar Fields with Zero Effective Energy and Euclidean Cycles in Cosmological Models

Free oscillations of scalar fields with a Higgs potential are investigated in cosmological models based on scalar fields, both in the case of isolated classical and phantom fields and in the case of an asymmetric scalar doublet. On the basis of numerical modeling, we have found dependences of the period of free oscillations with zero effective energy on the parameters of the field model and have also constructed energy spectra of the zero oscillations. These spectra display a thermal character, which allows us to interpret them as mass spectra of scalar bosons.

Qualitative and Numerical Analysis of a Cosmological Model Based on an Asymmetric Scalar Doublet with Minimal Connections. IV. Numerical Modeling and Types of Behavior of the Model

On the basis of a qualitative and numerical analysis of a cosmological model based on an asymmetric scalar doublet of nonlinear, minimally interacting scalar fields -- one classical and one phantom, peculiarities of the behavior of the model near zero energy hypersurfaces have been revealed. Numerical models have been constructed, in which the dynamical system has limit cycles on the zero-energy hypersurfaces. Three types of behavior of the cosmological model have been distinguished, configured by the fundamental constants of the scalar fields and the initial conditions. It is shown that over a wide sector of values of the fundamental constants and initial conditions, the cosmological models have a tendency to adhere to the zero-energy hypersurfaces corresponding to 4-dimensional Euclidean space.

Qualitative and Numerical Analysis of a Cosmological Model Based on an Asymmetric Scalar Doublet with Minimal Connections. III. Multiply-Connected Factor and Character of the Singular Points

On the basis of a qualitative and numerical analysis of a cosmological model based on an asymmetric scalar doublet of nonlinear, minimally interacting scalar fields, both classical and phantom, the behavior of the model near zero energy hypersurfaces has been revealed. The influence of the multiply connected factor of the phase space of the dynamical system, this factor being a consequence of the nonanalyticity of the coefficients of an autonomous system of differential equations, is discussed. The character of all singular points is revealed.

Peculiarities of Cosmological Models Based on a Nonlinear Asymmetric Scalar Doublet with Minimal Interaction. II. Numerical Analysis

We carry out a detailed analysis and numerical simulations of the evolution of cosmological models based on a doublet of classical and phantom scalar fields with self-interaction. 2D and 3D projections of the phase portraits of the corresponding dynamic system are built. Just as in the case of single scalar fields, the phase space of such systems becomes multiply connected, the ranges of negative total effective energy, unavailable for motion, appear there. A distinctive feature of the asymmetric scalar doublet is the time dependence of the forbidden range projections on the phase subspaces of each field, and, as a result, the existence of the limiting cycles with zero effective energy depends on the parameters of the field model and on the initial conditions. The numerical models are built where the dynamic system has limiting cycles on zero energy hypersurfaces. Three characteristic types of behavior of the cosmological model based on an asymmetric scalar doublet are identified.

Peculiarities of Cosmological Models Based on a Nonlinear Asymmetric Scalar Doublet with Minimal Interaction. I. Qualitative Analysis

Peculiarities of Cosmological Models Based on a Nonlinear Asymmetric Scalar Doublet with Minimal Interaction. I. Qualitative Analysis

Qualitative and Numerical Analysis of a Cosmological Model Based on an Asymmetric Scalar Doublet with Minimal Couplings. II. Numerical Modeling of Phase Trajectories

With the help of our own software package DifEqTools, numerical modeling of the cosmological evolution of a system consisting of an asymmetric scalar doublet of nonlinear, minimally interacting scalar fields, a classical field and a phantom field, has been performed. Peculiarities of the behavior of the model near zeroenergy hypersurfaces have been revealed.