Crystal Field Research Articles

Merging semi-crystallization and multispecies iodine intercalation at photo-redox interfaces for dual high-value synthesis

The artificial photocatalytic synthesis based on graphitic carbon nitride (g-C3N4) for H2O2 production is evolving rapidly. However, the simultaneous production of high-value products at electron and hole sites remains a great challenge. Here, we use transformable potassium iodide to obtain semi-crystalline g-C3N4 integrated with the I-/I3- redox shuttle mediators for efficient generation of H2O2 and benzaldehyde. The system demonstrates a prominent catalytic efficiency, with a benzaldehyde yield of 0.78 mol g−1 h−1 and an H2O2 yield of 62.52 mmol g−1 h−1. Such a constructed system can achieve an impressive 96.25% catalytic selectivity for 2e- oxygen reduction, surpassing previously reported systems. The mechanism study reveals that the strong crystal electric field from iodized salt enhances photo-generated charge carrier separation. The I-/I3- redox mediators significantly boost charge migration and continuous electron and proton supply for dual-channel catalytic synthesis. This groundbreaking work in photocatalytic co-production opens neoteric avenues for high-value synthesis.

Pressure-induced collapsed tetragonal transition in optimally Na-doped CaFe2As2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CaFe}}_{2} {\ ext{As}}_{2}$$\\end{document}

A comprehensive first-principles study on electronic structure of optimally doped Ca0.33Na0.67Fe2As2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\hbox {Ca}_{0.33}\\hbox {Na}_{0.67}\\hbox {Fe}_2\\hbox {As}_2}$$\\end{document} under hydrostatic pressures in the presence of magnetic configurations is presented. A magneto-structural transition from a tetragonal to a collapsed tetragonal phase at 3 GPa hydrostatic pressure is predicted in double-stripe antiferromagnetic configuration that corroborates experimental observations. As the system enters the non-superconducting collapsed phase, significant deviations occur in the local structural parameters compared to those at optimal Tc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\it{T}}_{c}$$\\end{document} values. This transition coincides with a sharp decrease in As density of states (DOS), accompanied by Fe magnetic moment collapse and substantial Fe square plane charge density modification. The structural transition induces a comprehensive reconstruction of the electronic structure, marked by distorted FeAs4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {FeAs}_{4}$$\\end{document} tetrahedra, potentially leading to unfavourable nesting conditions, and complete suppression of magnetism, correlating with the observed disappearance of superconductivity. Increasing pressure leads to a rise in crystal field splitting, influencing the spin-state transition in Ca0.33Na0.67Fe2As2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\hbox {Ca}_{0.33}\\hbox {Na}_{0.67}\\hbox {Fe}_2\\hbox {As}_2}$$\\end{document}, ultimately resulting in a shift from tetragonal to non-magnetic collapsed tetragonal phase as the Fe2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Fe}^{2+}$$\\end{document} spin state transitions to a low spin state. This demonstrates the intricate interplay between crystal field splitting, external pressure, and spin dynamics, highlighting the significant impact of magneto-volume effects on the structural phase of material under pressure.

RGB-tricolor multimodal luminescence of Ce3+ and Mn2+ in Mg2Al4Si5O18 via site occupancy engineering for anticounterfeiting applications

Multimodal luminescent materials have shown important applications in anti-counterfeiting and information encryption, however, mostly difficult to adjust optical properties with the structure, which leads to relatively constant emission position and less selectable excitation wavelength. Herein, Ce3+ and Mn2+ co-doped Mg2Al4Si5O18 phosphors are designed for the applications in RGB-tricolor multimodal anti-counterfeiting. Due to site occupancies, energy transfer and different thermal behaviors of Ce3+ and Mn2+ emissions, the emitting color of Mg2Al4Si5O18: Ce3+, Mn2+ is rich and tunable with different excitation wavelengths, doping concentrations and temperatures. The site occupancies of Ce3+ and Mn2+ are clarified with crystal field analysis and in-depth into transitions energies of Ce3+ and Mn2+. The energy transfer mechanism between Ce3+ and Mn2+ is analyzed via Inokuti-Hirayama model. The difference of thermal stabilities of Ce3+ and Mn2+ emissions is interpreted with construction of vacuum referred binding energy scheme. The as-designed molds of information encryption and decryption with Mg2Al4Si5O18: Ce3+, Mn2+ phosphors demonstrate the potential applications in anti-counterfeiting. The work provides an effective way for exploring Ce3+ and Mn2+ doped phosphors with RBG-tricolor multimodal luminescence.

Half-metallization Atom-Fingerprints Achieved at Ultrafast Oxygen-Evaporated Pyrochlores for Acidic Water Oxidation.

The stability and catalytic activity of acidic oxygen evolution reaction (OER) are strongly determined by the coordination states and spatial symmetry among metal sites at catalysts. Herein, an ultrafast oxygen evaporation technology to rapidly soften the intrinsic covalent bonds using ultrahigh electrical pulses is suggested, in which prospective charged excited states at this extreme avalanche condition can generate a strong electron-phonon coupling to rapidly evaporate some coordinated oxygen (O) atoms, finally leading to a controllable half-metallization feature. Simultaneously, the relative metal (M) site arrays can be orderly locked to delineate some intriguing atom-fingerprints at pyrochlore catalysts, where the coexistence of metallic bonds (M─M) and covalent bonds (M─O) at this symmetry-breaking configuration can partially restrain crystal field effect to generate a particular high-spin occupied state. This half-metallization catalyst can effectively optimize the spin-related reaction kinetics in acidic OER, giving rise to 10.3 times (at 188mV overpotential) reactive activity than pristine pyrochlores. This work provides a new understanding of half-metallization atom-fingerprints at catalyst surfaces to accelerate acidic water oxidation.

Impact of SnO2 doping on spectroscopic characteristics of the SnO2-Na2O-CoO-B2O3 borate glass matrix

The role of tin oxide (SnO2) on the structure-optical features of borate glasses containing low cobalt oxide impurities was studied. The study was carried out on a glass system [x SnO2 – (80-x) B2O3 – 19.5 Na2O – 0.5 CoO]; x = 0.0, 0.5, 1.0, 2.0 and 3.0 mol%. Glass synthesis was carried out by the melt-quench technique. Structure and optical absorption spectroscopy were carried out to explore the optical transitions of Co cations inside the present glass matrix. The obtained results indicate that, with the further addition of SnO2 content, the molar volume decreased from 31.675 cm3/mol to 29.147 cm3/mol. FTIR studies indicated the basic structural units of trigonal BO3 units and BO4 tetrahedra. Herein also, additional contents of tin oxide increased the nonbridging oxygen contents. The reason behind such increment is attributed to the existence of Sn4+ ions in octahedral coordination acting as network modifiers. Optical absorption spectra indicated the existence of Co ions in both Co2+ and Co3+ oxidation states. Moreover, the existence of significant SnO2 concurred with the significant blue shift in the visible absorption bands and red shift in near infrared absorption bands. The positions absorption bands of Co ions were analyzed in the context of ligand field parameters determinations. The obtained data of the crystal field splitting parameter (10Dqt) showed decreased values from 3451 cm−1 to 3364 cm−1 with more SnO2 addition. While Racah parameter B values were also, attained showing increased values from 967 cm−1 to 985 cm−1 when additional SnO2 is added. Further, the impacted role of SnO2 addition on the structural and optical properties of the present glasses was finally estimated.

Crystal field optimization, luminescence enhancement and thermal stability of novel K2NaAl0.4Ga0.6F6:Mn4+ solid solution red phosphor for high-performance warm WLED

Mn4+-doped fluoride phosphors have important application value in the background light and WLED lighting fields. Therefore, the synthesis of efficient and stable Mn4+-doped red phosphor is of great application value. In this study, a series of red-emitting K2NaAl1-yGayF6:xMn4+ (y = 0, 0.2, 0.4, 0.6, 0.8 and 1) (x = 0.01, 0.03, 0.05, 0.07 and 0.09) solid solution phosphors are successfully synthesized by simple coprecipitation method. The synthesis strategy of simple crystal structure optimization is proposed to realize simultaneously the crystal field optimization, luminescence enhancement and thermal stability of red phosphor. The calculation and theoretical analysis of crystal field strength are used to prove that solid solution matrix K2NaAl0.4Ga0.6F6 is the most ideal matrix material. X-ray powder diffraction, energy-dispersive X-ray spectrometer and scanning electron microscope are employed to determine the crystal structure, composition and morphology of all samples. Optical properties are characterized using excitation spectra, emission spectra and fluorescence lifetime curves. Moreover, the CIE coordinates of red-light show that the phosphor has low correlated color temperature and excellent color purity. Intriguingly, the as-prepared K2NaAl0.4Ga0.6F6:Mn4+ phosphor possesses admirable thermal quenching behavior and color stability at high temperature. At a temperature of 423 K, the photoluminescence intensity can be maintained at 52 % of the original intensity (298 K). The activation energy, the chromaticity shift and chromaticity coordinate variation are also systematically calculated. More importantly, A high-performance warm WLED with low correlated color temperature (CCT = 3982 K) and high color rendering index (Ra = 93.7) is achieved by using K2NaAl0.4Ga0.6F6:Mn4+ as a red-emitting material. These results demonstrate that K2NaAl0.4Ga0.6F6:Mn4+ red phosphor provides a novel choice for the warm WLED required for indoor lighting.

Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence.

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal-centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1→7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.

Enhanced luminescence performance in double perovskite CaSrLaSbO6: Mn4+ red emission phosphors for indoor plant growth via cation doping

Novel CaSrLaSbO6: Mn4+ red-emitting phosphors with double perovskite structure were successfully synthesized by the high-temperature solid-phase method. CaSrLaSbO6:Mn4+ phosphor showed a broad excitation band with different excitation peaks from 250 nm to 600 nm owing to the Mn4+-O2- charge transfer and 4A2g → (4T1g, 2T2g, and 4T2g) transitions of Mn4+ ions and exhibited intense deep-red emission at 678 nm attributed to the 2Eg → 4A2g transition of Mn4+ ions. To further enhance the performance of the phosphor, a cation doping method was adopted in this paper to synthesize CaSrLa1-xLnxSbO6: Mn4+ (Ln = Gd, Y) phosphors. The luminescence intensity of the samples was enhanced after doping with different cations, and the related mechanism was discussed. In addition, the microstructure and crystal field environment were systematically investigated. The luminescence intensity of the CaSrLa0.85Y0.15SbO6: Mn4+ phosphor was about 1.82 times higher than that of CaSrLaSbO6: Mn4+phosphor. The emission spectrum of the sample matched well with the absorption band of plant pigments. Furthermore, the plant growth LEDs and light-conversion film were prepared by using the optimized CaSrLa0.85Y0.15SbO6: Mn4+. The results indicate that the designed phosphors have great potential applications in agricultural cultivation.

Ca9-yMgyNaGd0.667(PO4)7:Eu2+: A Single Eu2+-Doped Full-Spectrum White Light Emission Phosphor with High Color Rendering Index.

The multi-cationic site occupation control of rare earth doped phosphor materials is one of the key factors in achieving single-phase full-spectrum emission. In this work, the site distribution of Eu2+ in Ca9NaGd0.667(PO4)7 (CNGP):x%Eu2+ phosphors with multi-cationic sites was determined. Under 385 nm excitation, CNGP:x%Eu2+ samples exhibited a cyan emission composed of three sub-Gaussian components. The CNGP:1.5%Eu2+ phosphor was structurally modified through the partial substitution of Mg2+ for Ca2+ according to the crystallographic site engineering theory, and corresponding luminescent properties had been adjusted. When the concentration of Mg2+ changed, the Ca9-yMgyNaGd0.667(PO4)7:1.5%Eu2+ (CNGPE:yMg2+) phosphors exhibited a tunable emission from cyan to orange and achieved white light emission at y = 0.6. Based on the change of the crystal field environment, the mechanism of Mg2+ substitution affecting the luminescence characteristics of CNGP:x%Eu2+ phosphors was researched in detail. The light-emitting diode device consisted of a CNGPE:0.6Mg2+ phosphor and a 385 nm chip and had a high color rendering index (CRI = 91.9), low correlated color temperature (CCT = 4852 K), and excellent color stability. The optical performance of this device makes it promising to be used in full spectrum lighting.

X-ray spectroscopic investigation of crystal fields in Ce2Rh1−xIrxIn8 heavy fermions

The higher dimensionality in the crystal fields of the Ce2MIn8 (M=Rh,Ir) compounds and its interplay with hybridization and disorder are key ingredients to understand the complex phase diagrams by this family, which have been explored extensively by macroscopic techniques. Here, we present an investigation of the crystal-electric field schemes of Ce2Rh1−xIrxIn8 using x-ray absorption spectroscopy. Our full multiplet calculations for the 4f1 configuration of Ce3+ to describe the temperature-dependent linear dichroism in Ce2MIn8 are consistent with a Γ71=1−α2·|∓32〉−|α|·|±52〉 ground state containing a predominant |±3/2〉 contribution that increases further with x. This enhancement is believed to favor superconductivity in Ce-based heavy fermion materials, observed in previous results in the CeMIn5 family. Our recent observations shed light on the unexpected emergence of the ambient-pressure superconducting dome in the center of the composition phase diagram and its subsequent suppression on the Ir-rich side due to the early onset of fluctuations associated with the structurally more disordered state, inferred from previous neutron magnetic diffraction experiments. Published by the American Physical Society 2024

Electronic Structure of a Neodymium(III) Tris(oxidiacetate) Complex from Luminescence Data and Ab Initio Calculations.

Neodymium(III) is a near-infrared emissive and magnetic ion, which has found use in various high-technology applications. Yet, accurate predictions of the luminescent and magnetic properties of neodymium(III) based on the coordination environment remain to be done. Guidelines exist, but to build structure-property relationships for this element, more data are needed. Herein, we present a high-symmetry starting point. The tris(oxidiacetate) complex of neodymium(III) was prepared and crystallized, and access to the experimentally determined structure allowed us to quantify the symmetry of the compound and to perform calculations directly on the same structure that is investigated experimentally. The luminescent properties were determined and the electronic structure was computed using state-of-the-art ab initio methods. All electronic transitions in the range from 490 to 1400 nm were mapped experimentally. Using a Boltzmann population analysis, the combination of the excitation and emission spectra revealed the crystal field splitting of the 18 lowest-energy Kramers levels that experimentally could be unambiguously resolved. This assignment was supported by ab initio calculations, and the crystal field splitting was well reproduced. The electronic structure reported for the tris(oxidiacetate) complex was used to deduce the coordination structure in aqueous solution. Finally, the results are compared to empirical trends in the literature for the electronic structure of neodymium(III).

Anisotropic excitonic magnetism from discrete C4 symmetry in CeRhIn5

Anisotropy in strongly correlated materials is a central parameter in determining the electronic ground state and is tuned through the local crystalline electric field. This is notably the case in the CeCoxRh1−xIn5 system where the ground-state wave function can provide the basis for antiferromagnetism and/or unconventional superconductivity. We develop a methodology to understand the local magnetic anisotropy and experimentally investigate with neutron spectroscopy applied to antiferromagnetic (TN=3.8K) CeRhIn5, which is isostructural to d-wave superconducting (Tc=2.3K) CeCoIn5. Through diagonalizing the local crystal field Hamiltonian with discrete tetragonal C4 point group symmetry and coupling these states with the random phase approximation, we find two distinct modes polarized along the crystallographic c and a−b planes, agreeing with experiment. The anisotropy and bandwidth, underlying the energy scale of these modes, are tuneable with a magnetic field which we use experimentally to separate in energy single and multiparticle excitations thereby demonstrating the instability of excitations polarized within the crystallographic a−b plane in CeRhIn5. We compare this approach to a Seff=12 parametrizations and argue for the need to extend conventional SU(2) theories of magnetic excitations to utilize the multilevel nature of the underlying crystal-field basis states constrained by the local point-group C4 symmetry. Published by the American Physical Society 2024

Antipolar 2D Metallicity with Tunable Valence Wx+ (5 ≤ x ≤ 5.6) in the Layered Monophosphate Tungsten Bronzes [Ba(PO4)2]WmO3m-3.

The newly discovered series of layered monophosphate tungsten bronzes (L-MPTB) [Ba(PO4)2]WmO3m-3 consist of m-layer-thick slabs of WO6 octahedra separated by barium-phosphate spacers. They display a 2D metallic behavior confined in the central part of the perovskite slabs. Here, we report the missing m = 2 member of this series, containing the rather uncommon W5+ oxidation state. We have analyzed its structure-property relationships in relation to the other members of the L-MPTB family. In particular, we have determined its crystal structure by means of single-crystal X-ray and electron diffraction and investigated its physical properties from resistivity, Seebeck-coefficient and heat-capacity measurements combined with first-principles calculations. All the L-MPTB compounds show metallic behavior down to 1.8 K without any clear charge-density-wave (CDW) order. The m = 2 member, however, displays an increased influence of the spacer that translates into anisotropic negative thermal expansion, reversed thermopower and reversed crystal-field splitting of the tungsten t2g orbitals. Our analysis of the full [Ba(PO4)2]WmO3m-3 series reveals a systematic and significant W off-centering in their octahedral coordination. We identify the resulting anti-polar character of these W displacements as the crucial aspect behind the 2D metallicity of these systems: It leads to the presence of bound charges whose screening determines the distribution of mobile charges, tending to accumulate at the center of the [WmO3-m] block. We argue that this mechanism is analogous to enhanced conductivity observed for charged domain walls in ferroelectrics, thus providing a general design rule to promote 2D metallicity in layered systems.

Magnetic and electronic properties of double perovskite Sr2CrMoO6 for spintronic applications: Insights from first-principles and Monte Carlo approaches

Abstract In this work, we studied the electronic and magnetic properties of the double perovskite Sr2CrMoO6 using ab initio calculations with Generalized Gradient Approximation (GGA) and Monte Carlo (MC) simulations. The compound has two magnetic sublattices: one occupied by Mo5+ with spin (S = 1/2) and the other by Cr3+ with spin (σ = 3/2). The results showed half-metallic behavior with a total magnetic moment of 2.0 μB. Using Monte Carlo simulations, we investigated the phase transitions and observed interesting phenomena such as a critical endpoint and both second-order and first-order phase transitions. Additionally, the results revealed compensation points for specific values of the crystal field.

A coupled crystal inelasticity-phase field model for crack growth in polycrystalline nitinol microstructures

Abstract This paper introduces a comprehensive computational framework, comprising a finite deformation crystal inelasticity constitutive model and phase field model, for modeling crack growth in superelastic nitinol polycrystalline microstructures. The crystal inelasticity model represents crystal stretching and lattice rotation from elastic mechanisms, as well as local inelastic deformation due to austenite-martensite phase transformation. The phase field formulation decomposes the Helmholtz free energy density into stored elastic energy, phase transformation energy, and crack surface energy components. The elastic energy accounts for tension-compression asymmetry with the formation of the crack through a spectral decomposition. Kinetic Monte Carlo simulations generate equilibrium area fractions of different surface orientations, which serve as weights for the surface energy. An adaptive wavelet-enhanced hierarchical finite element (FE) model is introduced to alleviate high computational overhead in phase field crack simulations. Simulations with the coupled inelasticity phase field model are conducted under various loading conditions including Mode-I tension, a quasi-static Kalthoff experiment, and cyclic loading of polycrystalline microstructures. Crack propagation is effectively predicted by this model, providing valuable insights into the material mechanical behavior with growing cracks.

Oxygen vacancy-mediated activation of Zn-O bonds at the S-scheme heterostructure interface for efficient uranium collection and resistance to biological contamination

Efficient reduction of U(VI) to U(IV) during seawater uranium extraction remains a challenge. Here, cerium dioxide quantum dots were bonded to the surface of indium zinc sulfide (ZIS) to form ZIS composite cerium dioxide quantum dots (ZIS/QDs-Ce). The oxygen vacancies are able to activate the Zn-O bonds at the ZIS and QDs-Ce interfaces, thus enabling the constructed S-scheme heterojunction to show great potential in facilitating the separation and transfer of photogenerated carriers. ZIS/QDs-Ce exhibited high anti-bio-pollution activity by generating biotoxic free radical reactive oxygen species (ROS). The photo-induced reduction of uranium by ZIS/QDs-Ce in 10 ppm uranium spiked simulated seawater reached 99.6 %. Oxygen vacancies cause distortions in the crystal field, and the Zn-O bond activation process triggers the movement of ZIS/QDs-Ce from the singlet low-spin state to the stable triplet state, resulting in free-carrier trapping centers and optimized electronic energy band structures. ZIS/QD-Ce has superior uranium extraction capabilities and is highly recommended for uranium extraction from seawater.

Anisotropic magnetic and quadrupolar H−T phase diagram of CeRh2As2

The tetragonal heavy-fermion compound CeRh2As2 has intriguing low-temperature symmetry-breaking phases whose nature is unclear. The unconventional superconducting phase is complemented by other normal-state phases which presumably involve ordering of 4f electron multipoles supported by the Kramers doublets split by the tetragonal crystal electric field (CEF). The most striking aspect is the pronounced anisotropic H−T phase boundary for in-plane and out-of plane field directions. Using a localized 4f CEF model we demonstrate that its essential features can be understood as the result of competing low-field easy-plane magnetic order and field-induced quadrupolar order of xy type. We present calculations based on coupled multipole random phase approximation response function approach as well as molecular field treatment in the ordered regime. We use an analytical approach for a reduced quasiquartet model and numerical calculations for the complete CEF level scheme. We discuss the quantum critical properties as function of multipolar control parameters and explain the origin of a pronounced ac anisotropy of the H−T phase diagram. Finally, the field and temperature evolution of multipolar order parameters is derived and the high-field phase diagram is predicted. Published by the American Physical Society 2024

Ultrabroadband Long-Wavelength Near-Infrared MgIn2O4:Ni2+ Phosphor Synthesized via Sol-gel Combustion Method as a Light Source for Night Vision Imaging, Nonvisual Detection, and Anticounterfeiting Display.

Long-wavelength near-infrared (LWNIR) imaging technology has exciting application potential across various fields due to its ability of deeper penetration and unique properties related to its emission wavelength, when compared to short-wavelength near-infrared imaging. However, the limited availability of materials for LWNIR light sources, due to the lack of suitable host materials that constitute luminescence centers, has been a major challenge and technical obstacle in realizing such applications. Here, we developed MgIn2O4:Ni2+ phosphors with an antispinel structure and LWNIR luminescence properties through a sol-gel combustion method. Under excitation at 365 nm, its emission wavelength covers the range of 1000-2000 nm, with a peak emission at approximately 1520 nm, a full width at half-maximum of ∼340 nm, and an optimized photoluminescence quantum yield of ∼21.22%, when an optimal Ni2+ doping content of 1 mol % was used. Studies on the crystal structure of MgIn2O4 have shown that Ni2+ ions preferentially replace the lattice position occupied by Mg2+ ions in the [MgO6] octahedrons, which provides a crystal field microenvironment of weak strength to the Ni2+ luminescence centers and promotes their LWNIR emission with a large Stokes shift. A LWNIR pc-LED device was assembled using the optimized MgIn2O4:Ni2+ phosphor and a near-ultraviolet LED chip (@ 365 nm), and its potential applications, including NIR night vision imaging, nonvisual detection, and anticounterfeiting displays, were demonstrated. Our results show that the antispinel MgIn2O4:Ni2+ phosphor prepared by the sol-gel combustion method is a promising LWNIR luminescence material.

Insight into compensation behaviors and hysteresis characteristics of an Ising-type borophene monolayer

Abstract Boron is another novel two-dimensional material after graphene with splendid chemical and physical properties and potential applications in magnetism, electronics, energy materials and other fields. Studying the magnetic properties of borophene is important to improve the relevant theories and experiments. In this paper, we extend a single spin-3/2 Ising model to analyze the magnetic characteristics of the borophene monolayer by using Monte Carlo simulation. The influence of crystal field, exchange coupling and external magnetic field on the magnetization, magnetic susceptibility and internal energy are studied separately and the phase diagrams are presented. The calculation indicates that the system presents the compensation temperature and triple-loop hysteresis behaviors.

Improved performance of temperature sensors based on the one-dimensional topological photonic crystals comprising hyperbolic metamaterials

This paper seeks to progress the field of topological photonic crystals (TPC) as a promising tool in face of construction flaws. In particular, the structure can be used as a novel temperature sensor. In this regard, the considered TPC structure comprising two different PC designs named PC1 and PC2. PC1 is designed from a stack of multilayers containing Silicon (Si) and Silicon dioxide (SiO2), while layers of SiO2 and composite layer named hyperbolic metamaterial (HMM) are considered in designing PC2. The HMM layer is engineered using subwavelength layers of Si and Bismuth Germinate, or BGO (Bi4Ge3O12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Bi}}_{4}{\ ext{Ge}}_{3}{\ ext{O}}_{12}$$\\end{document}). The mainstay of our suggested temperature sensor is mainly based on the emergence of some resonant modes inside the transmittance spectrum that provide the stability in the presence of the geometrical changes. Meanwhile, our theoretical framework has been introduced in the vicinity of transfer matrix method (TMM), effective medium theory (EMT) and the thermo-optic characteristics of the considered materials. The numerical findings have extensively introduced the role of some topological parameters such as layers’ thicknesses, filling ratio through HMM layers and the periodicity of HMM on the stability or the topological features of the introduced sensor. Meanwhile, the numerical results reveal that the considered design provides some topological edge states (TESs) of a promising robustness and stability against certain disturbances or geometrical changes in the constituent materials. In addition, our sensing tool offers a relatively high sensitivity of 0.27 nm/°C.