Crystal Field Research Articles

Revisiting the Optical Spectrum of the Plutonyl Ion (PuO2)2+ in 1 M HClO4.

The analysis of the solution absorption spectrum of the plutonyl ion in an aqueous environment was given by Eisenstein and Pryce (E&P) in 1968. In 2011 a new spectrum was published of the (PuO2)2+ ion in 1 M HClO4. We have been provided with the original data of this spectrum and have found in the data a previously unreported low-lying transition at 7385 cm-1 which we have assigned as a magnetic dipole transition. We have fit most of the near-infrared and optical transitions with Gaussian fits and tabulated a new energy level list up to 22,000 cm-1 which mostly agrees with the data of E&P. We assumed a crystal field of D∞h (only axial symmetry) and utilized the intensity calculations published for the isoelectronic (NpO2)1+ ion using a complete basis set for the 5f2 problem including the Coulombic, spin-orbit as well as the crystal field Hamiltonian. Our results differ substantially from those of E&P. Subsequently, we used a truncated Hamiltonian to try to establish the effects of assuming the σ antibonding orbitals are at such high energies that we can ignore their contributions to the lower lying φ and δ orbitals.

Ca2+/Si4+ Modification of the (Gd,Lu)AG Garnet for Enhanced Broadband Cr3+ Luminescence of High Thermal Stability.

Near-infrared (NIR)-emitting phosphors with high quantum efficiency and thermal stability are crucial to NIR pc-LEDs. Garnet-structured (GdLuCa)(Al4-zSiCrz)O12 (z = 0.01-0.2) and (Gd2-xLuCax)(Al4.95-xSixCr0.05)O12 (x = 0.2-1.0) new phosphors with promising NIR luminescence under blue light excitation were designed and fabricated by a solid-state reaction in this work. It was analyzed that the Ca2+, Cr3+, and Si4+ ions would replace Gd3+ in [GdO8], Al1 in [Al1O6], and Al2 in [Al2O4], respectively, and the optimal Cr3+ content is z = 0.05, above which concentration quenching would occur via an electric dipole-dipole interaction. Increasing Ca2+/Si4+ substitution up to x = 1.0 led to luminescence enhancement by a factor of up to 1.85 and internal/external quantum efficiency (%) increment from ∼25.9/10.7 to 63.4/27.5, and all of the phosphors showed excellent thermal stability (I423K/I298K ≥ 87.6%). The luminescence properties of Cr3+ were discussed in detail through systematic investigation of the effects of Cr3+ and Ca2+/Si4+ contents on the crystal structure, local coordination, and crystal field. With the NIR pc-LED device integrated from the optimal phosphor (x = 1.0) and a blue LED chip, electroluminescence manifested potential applications in night vision and medical diagnosis.

Optimization of the Skanavi model and its application to high permittivity materials

Abstract In this paper, a novel method is introduced to optimize the traditional Skanavi model by decomposing the electric field of molecules into the electric field of ions and quantitatively describing the ionic-scale electric field by the structural coefficient of the effective electric field. Furthermore, the optimization of the Skanavi model is demonstrated and the ferroelectric phase transition of BT crystals is revealed by calculating the optical and static permittivities of BaTiO3, CaTiO3, and SrTiO3 crystals and the structure coefficients of the effective electric field of BT crystals after Ti4+ displacement. This research compensates for the deficiencies of the traditional Skanavi model and refines the theoretical framework for analyzing dielectric properties in high permittivity materials.

Crystal field magnetostriction of spin ice under ultrahigh magnetic fields

Crystal field magnetostriction of spin ice under ultrahigh magnetic fields

Orbitronics: Mechanisms, Materials and Devices

AbstractSpintronics has been extensively explored over the past decades, focusing primarily on the spin characteristic of the electron, while the orbital feature of the electron has been conventionally assumed to be quenched by the crystal field effect. Recently, studies have unveiled a fascinating discovery that orbital current, originating from orbital effects, can be generated in materials with weak spin‐orbit coupling by applying electric fields, enabling the manipulation of the ferromagnetic magnetization and induction of terahertz emission. This review highlights recent achievements in orbital effects, materials, and devices, beginning by discussing the mechanisms underlying orbital effects, e.g. the orbital Hall effect, orbital Rashba‐Edelstein effect, inverse orbital Hall effect, and inverse orbital Rashba‐Edelstein effect. Subsequently, a wide range of materials exhibiting orbital effects are classified and the orbital sources in them are identified. Furthermore, the review introduces the orbital torque devices and the orbital terahertz emitters, summarizing the in‐depth mechanisms of the orbital torque, orbital torque efficiency, and orbital diffusion length across various material structures. Additionally, the review presents strategies for enhancing orbital torque efficiency and driving magnetization switching. These efforts aim to explore the potential applications for orbitronic memory devices, computing components, and terahertz emitters.

Self‐adaptive Coordination Evolution Mediated Pore‐Space‐Partition in Metal–Organic Frameworks for Boosting SF6/N2 Separation

AbstractThe controllable and precise structural regulation of metal–organic frameworks (MOFs) based on isoreticular chemistry is an effective strategy for creating functional material platforms, such as efficient porous adsorbents. Herein, for the first time, mediated by an unprecedented self‐adaptive coordination evolution (SACE) on pseudo‐D2h‐symmetric [M4(μ3‐O)2(COO)6] (M=Mn/Fe) clusters, two pore space partitioned MOFs (CTGU‐47‐Mn/Fe, CTGU=China Three Gorges University) have been successfully constructed. Owing to the more confined adsorption space and dense binding sites produced by pore space partitioning (PSP), the CTGU‐47‐Mn/Fe exhibit significantly enhanced performance in the capture or recovery SF6 (greenhouse/electronic specialty gas) from SF6/N2 mixture compared to their non‐partitioned homologous structures (CTGU‐46‐Mn/Fe) with adsorption selectivity increased from 37/72 to 634/157 (v/v, 10/90, 100 kPa). The theoretical calculations also elucidated that the implementation of PSP within CTGU‐47‐Mn/Fe leads to dramatically strengthened binding affinity for SF6 over N2 through extra multiple F⋅⋅⋅H interactions. This study represents a valuable advance in crystal engineering field: the SACE of polynuclear metal clusters is expected to be useful in the structural regulation of MOFs and the fabrication of advanced porous adsorbents.

Spin-orbit entangled moments and magnetic exchange interactions in cobalt-based honeycomb magnets BaCo2(XO4)2 (X = P, As, Sb)

Co-based honeycomb magnets have been actively studied recently for the potential realization of emergent quantum magnetism therein such as the Kitaev spin liquid. Here we employ density functional and dynamical mean-field theory methods to examine a family of the Kitaev magnet candidates BaCo2(XO4)2 (X = P, As, Sb), where the compound with X = Sb being not synthesized yet. Our study confirms the formation of Mott insulating phase and the Jeff = 1/2 spin moments at Co2+ sites despite the presence of a sizable amount of trigonal crystal field in all three compounds. The pnictogen substitution from phosphorus to antimony significantly changes the in-plane lattice parameters and direct overlap integral between the neighboring Co ions, leading to the suppression of the Heisenberg interaction. More interestingly, the marginal antiferromagnetic nearest-neighbor Kitaev term changes sign into a ferromagnetic one and becomes sizable at the X = Sb limit. Our study suggests that the pnictogen substitution can be a viable route to continuously tune magnetic exchange interactions and to promote magnetic frustration for the realization of potential spin liquid phases in BaCo2(XO4)2.

Highly efficient tunable mid-infrared luminescence achieved by crystal field modulation of CsPb1-xHoxBr3 halide perovskite AlF3-based fluoride glass

Mid-infrared (MIR) light sources have gained significant importance across various applications in spectroscopy, sensing, astronomy, communications and medical surgery. The diverse spectral characteristics of rare earth ions, particularly lanthanide ions, stemming from their distinctive 4f intershell transitions, offer a multitude of potential transitions spanning the UV-visible-infrared spectrum. Despite recent advancements in MIR gain luminescence, the investigation of tunable MIR luminescence mechanisms remains a major technical challenge. Herein, an effective mechanism to modulate the local crystal field of rare earth ions by altering its crystal structure has been revealed, resulting in tunable broad-spectrum emission in the MIR luminescence range of 2800-3000 nm and multi-peak emission in the near-infrared band of Ho3+. Notably, the local crystal field of Ho3+ is adjusted by manipulating the lattice symmetry of CsPb1-xHoxBr3 perovskite through the incorporation of fluoride glass reticulation to control the crystal size of the perovskite and thereby modify the lattice symmetry of CsPb1-xHoxBr3 perovskite. The energy level transition of Ho3+ is influenced by adjusting the crystal field asymmetry, resulting in the splitting of the 5I6 energy level depending on the crystal field. This cleavage affects the transitions from the 5I5 level to 5I6 at 1480 nm and from 5I6 to 5I7 at 2880 nm. As 5I6 acts as the common upper level for the two emission peaks, the infrared peaks at 1480 nm and 2880 nm widen and develop into a dual-peak emission phenomenon. The infrared luminescence produced aligns closely with the distinctive infrared absorption peaks of carbon dioxide, leading to the development of a convenient, high-precision device for monitoring of CO2 concentration in hydrogen energy in real time. These findings are anticipated to pave the way for extensive utilization of novel tunable MIR luminescence.

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has establised that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Intervalence charge transfer in aluminum oxide and aluminosilicate minerals at elevated temperatures

Abstract Single-crystal optical spectra of corundum (Al2O3) and the Al2SiO5 polymorphs andalusite, kyanite, and sillimanite, containing both Fe2+-Fe3+ and Fe2+-Ti4+ intervalence charge transfer (IVCT) absorption bands were measured at temperatures up to 1000 °C. Upon heating, thermally equilibrated IVCT bands significantly decreased in intensity and recovered fully on cooling. These trends contrast with the behavior of crystal field bands at temperature for Fe, Cr, and V in corundum, kyanite, and spinel. The effects of cation diffusion and aggregation, as well as the redistribution of band intensity at temperature, are also discussed. The loss of absorption intensity in the visible and near-infrared regions of the spectrum of these phases may point to a more general behavior of IVCT in minerals at temperatures within the Earth with implications for radiative conductivity within the Earth.

Bilayer graphene like-structure in the presence of a time-dependent magnetic field

In this work we consider the dynamic magnetic characteristics induced by a time-dependent magnetic field in the case of a bilayer graphene-like structure. We pay special attention to the influence of the crystal field parameter and exchange interaction parameter on the hysteresis behavior. Among the most interesting magnetic phenomena that have been studied in this work, to understand phase transitions in the system within the framework of the spin-7/2 Ising model and dynamic mean-field theory, include coercivity, remanent magnetization, and the appearance of multiple hysteresis loops. Temperature, exchange interaction parameter, and crystal field parameter can all be used to regulate the system's phase transitions and hysteresis loop types. These parameters will define the magnetic properties of a system that is allowed to take a structure similar to that of bilayer graphene and thereby impact applications related to the development of sophisticated sensors, low energy loss systems, and magnetic storage devices.

Pyrochlore-like Local Structure in Globally Disordered Y2Zr2O7: Evidence and Reasoning by Combined Theoretical and Experimental Study.

Even though technological relevance for nuclear and oxide fuel cell application has persuaded a large number of investigations on the Y2Zr2O7 system, its local structure still remains ambiguous and debatable. While diffraction-based investigations claim a lack of local ordering, the MAS NMR and Raman spectroscopic investigations speculate the presence of local ordering. Besides, a correlation between the local and global structures of Y2Zr2O7 is also missing to date. Present work attempts to get deeper insights into the local structure of Y2Zr2O7 and correlate the local structure with global disordering. Complementary investigation using multiple strategies (XRD, RAMAN, electron microscopy, DFT calculations) revealed the presence of pyrochlore-like features in globally disordered Y2Zr2O7. Globally distributed "local probe ions" (Sn4+ by MAS NMR and Eu3+ by photoluminescence (PL)) were utilized for establishing the correlation between local and global structures. The 119Sn MAS NMR spectra possess the shoulder peak bearing chemical shift values, which are improbable under complete cationic randomization. The emission and decay profiles of the Eu3+ ion recommend positioning of few probe ions at the centrosymmetric site, which was further reinforced by crystal field splitting and lifetime values. Thus, both NMR and PL results reaffirm the existence of a pyrochlore-like atomic arrangement in predominantly defective fluorite Y2Zr2O7 phase. These discernible pyrochlore-like features have been envisaged to be emanating from unevenness in bond strength and ionicity/covalency of Y-O and Zr-O bonds. Cationic and anionic randomization energetically endorses global disordering, but the bonding disparity induces short-range ordering. It is believed that the presented findings will guide future research in regulating the physicochemical properties of Y2Zr2O7 for the target applications.

Magnetic Behavior and Compensation Temperature in Sulflower-Like Nanostructures: A Monte Carlo Study

This study delves into the magnetic behavior of sulflower-like nanostructures, particularly focusing on compensation and blocking temperatures. Through the construction of a phase diagram detailing crystal and external magnetic fields (D/[Formula: see text], H/[Formula: see text], stable phases were identified, shedding light on how spin configurations evolve with variations in H/[Formula: see text] and D/[Formula: see text]. The analysis of blocking temperature ([Formula: see text]/[Formula: see text] and compensation temperature ([Formula: see text]/[Formula: see text] relative to [Formula: see text]/[Formula: see text], [Formula: see text]/[Formula: see text] and H/[Formula: see text] reveals intriguing patterns. Additionally, an examination of hysteresis cycles uncovers dynamic behavior, characterized by multiple loops and magnetization plateaus. These findings open promising avenues for spintronic applications of sulflower-like nanostructures, offering valuable insights into their magnetic behavior and potential utility in future technologies. This involves the fabrication of high-density data storage devices, where its tunable magnetic characteristics may result in the development of effective data manipulation and storage components.

Precisely Engineering of Ångström‐Scale Dual Single Atom Drive [Co‐O] Spin‐Orbit Coupling to Boost Lithium–Oxygen Batteries Electrocatalysis

AbstractDual‐atom catalysts (DACs) have emerged as a novel area of investigation in lithium–oxygen (Li‐O2) batteries due to their distinctive synergistic mechanisms. However, achieving precise control of the active site structure and unraveling the synergistic effects of bimetallic species remains a significant challenge. Here, the study reports a pre‐encapsulated pyrolysis strategy using a Co‐based Robson‐type binuclear complex as a precursor to mediate the synthesis of dual single‐atom Co (Co‐DAC) with precise angstrom‐scale inter‐site distance configuration, serving as an efficient catalyst for Li‐O2 batteries. The tailored structure induces significant charge redistribution, reducing crystal field splitting energy (ΔO). The high‐spin Co species generate a strong electronic driving force, forming flexible σ and δ‐like bonds with the crucial oxygen intermediate (*O). Simultaneously, enhanced Co‐O spin‐orbit coupling facilitates electron transport along the bridging O‐channel, forming highly active Co‐O‐O‐Co electron chains that synergistically adsorb *O, establishing a favorable reaction pathway. Significant optimization of Li‐O2 batteries redox kinetics is achieved based on the well‐defined local structure of dual single‐atom Co sites. This work enhances the understanding of the dependence between rational design of custom structures and corresponding electron transfer dynamics, while providing new strategies and theoretical guidance for DACs to help develop high‐performance Li‐O2 batteries.

Self-adaptive Coordination Evolution Mediated Pore-Space-Partition in Metal-Organic Frameworks for Boosting SF6/N2 Separation.

The controllable and precise structural regulation of metal-organic frameworks (MOFs) based on isoreticular chemistry is an effective strategy for creating functional material platforms, such as efficient porous adsorbents. Herein, for the first time, mediated by an unprecedented self-adaptive coordination evolution (SACE) on pseudo-D2h-symmetric [M4(μ3-O)2(COO)6] (M = Mn/Fe) clusters, two pore space partitioned MOFs (CTGU-47-Mn/Fe, CTGU = China Three Gorges University) have been successfully constructed. Owing to the more confined adsorption space and dense binding sites produced by pore space partitioning (PSP), the CTGU-47-Mn/Fe exhibit significantly enhanced performance in the capture or recovery SF6 (greenhouse/electronic specialty gas) from SF6/N2 mixture compared to their non-partitioned homologous structures (CTGU-46-Mn/Fe) with adsorption selectivity increased from 37/72 to 634/157 (v/v, 10/90, 100 kPa). The theoretical calculations also elucidated that the implementation of PSP within CTGU-47-Mn/Fe leads to dramatically strengthened binding affinity for SF6 over N2 through extra multiple F···H interactions. This study represents a valuable advance in crystal engineering field: the SACE of polynuclear metal clusters is expected to be useful in the structural regulation of MOFs and the fabrication of advanced porous adsorbents.

Observation of two-dimensional time-reversal broken non-Abelian topological states

Going beyond the conventional theory, non-Abelian band topology reveals the global quantum geometry of multiple Bloch bands and unveils a new paradigm for topological physics. However, to date, experimental studies on non-Abelian topological states beyond one dimension are still restricted to systems with time-reversal (T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{T}}}$$\\end{document}) symmetry. Here, exploiting a designer gyromagnetic photonic crystal, we find rich T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{T}}}$$\\end{document}-broken non-Abelian topological phases and their transitions with an unexpected connection to multigap antichiral edge states. By in-situ tuning the magnetic field in the gyromagnetic photonic crystal, we can create, braid, merge, and split the non-Abelian topological nodes in a unique way. Alongside this process, the multigap antichiral edge states can be tuned versatilely, giving rise to topological edge waveguiding with frequency-dependent directionality. These findings open a new avenue for non-Abelian topological physics and topological photonics.

Pressure-Induced Structural Phase Transition and Fluorescence Enhancement of Double Perovskite Material Cs2NaHoCl6

Cs2NaHoCl6, a double perovskite material, has demonstrated extensive application potential in the fields of anti-counterfeiting and optoelectronics. The synthesis of Cs2NaHoCl6 crystals was achieved using a hydrothermal method, followed by the determination of their crystal structures through single crystal X-ray diffraction techniques. The material exhibits bright red fluorescence when exposed to ultraviolet light, confirming its excellent optical properties. An in situ high-pressure fluorescence experiment was conducted on Cs2NaHoCl6 up to 10 GPa at room temperature. The results indicate that the material possibly undergoes a structural phase transition within the pressure range of 6.9–7.9 GPa, which is accompanied by a significant enhancement in fluorescence. Geometric optimization based on density functional theory (DFT) revealed a significant decrease in the bond lengths and crystal volumes of Ho-Cl and Na-Cl across the predicted phase transition range. Furthermore, it was observed that the bond lengths of Na-Cl and Ho-Cl reach an equivalent state within this phase transition interval. The alteration in bond length may modify the local crystal field strength surrounding Ho3+, consequently affecting its electronic transition energy levels. This could be the primary factor contributing to the structural phase transition.

Environmentally-Friendly Europium-Based Yellow Perovskite Nanocrystals with Near-Unit Efficiency for White LED.

Recently, Mn2+-doped metal halide perovskites (MHPs) have been extensively studied as they can improve the photoluminescence quantum yield (PLQY) with minimal self-absorption. However, almost all of them with high efficiency are Pb/Cd-based toxic heavy metal perovskites, which seriously limits their commercial applications. To address the dual needs of high efficiency and environmental protection, this study proposes to incorporate Mn2+ into the environmentally friendly perovskite CsEuX3 (X = Cl/Br), and further increases PLQY to 96.9% through the codoping of Tb3+, which, to the best of our knowledge, is the highest reported value of all inorganic environmentally friendly perovskites in the visible light region. It is found that the codoping of Tb3+ can reduce the host defect density and enhance the crystal field strength around Mn2+, acting as an energy transfer bridge. Additionally, Mn2+/Tb3+-codoped CsEuX3-based white light-emitting diodes (WLEDs) with a high color rendering index (Ra = 91.2) demonstrate potential for lighting applications.

Soft Phononic Crystal with Tunable Bandgap Through Pneumatic Actuation

Pneumatic manipulation has the advantages of low cost, lightweight design, fast response, and ease of integration. However, its application in the field of phononic crystals remains limited. Inspired by pneumatic soft robots, this article proposes a pneumatic soft phononic crystal arranged in a square lattice, incorporating four pneumatic actuators within the scatterer. By manipulating air pressure, the bandgap can be effectively opened and closed. The finite element analysis is employed to examine the deformation and bandgaps of the pneumatic soft phononic crystal under varying air pressures. Moreover, the effect of the scatterer's rotation angle on the bandgap evolution in the phononic crystal is parametrically investigated. The results show that varying both the volume and the rotation angle of the scatterer can achieve bandgap opening, closing, and tuning. The proposed phononic crystal presents obvious practical applications and provides important insights for the design of soft‐tunable acoustic devices.

Impact of the Lead‐Free Crystal Matrix 0.94NBaTiO3‐0.06SrTiO3 on the Photoluminescence Properties of Eu+3

The investigation reveals that the crystal field environment induces photoluminescence in Eu3+. These synthesized materials hold promise for a wide array of commercial applications, particularly in the light emitting diode industry, representing a significant advancement for the current generation of technology. The lead‐free electroceramics 0.94NB1−xEuxTiO3‐0.06SrTiO3 (x = 0 and x = 0.1) are fabricated using the conventional solid‐state reaction technique. Within these ceramics, both rhombohedral (R3c) and tetragonal (P4mm) structural phases coexist. The structural conformation and fluctuations in average grain size indicate the successful substitution of Eu3+ in 0.94NB1−xTiO3‐0.06SrTiO3 (x = 0). The incorporation of Eu3+ ions into the host matrix induces a long‐range ferroelectric state, marked by a rhombohedral (R3c) distortion, alongside enhanced tetragonal (P4mm) features. This structural modification results from the interaction between the Eu3+ ions and the host lattice, which fosters the emergence of a ferroelectric polarization. The coexistence of rhombohedral and tetragonal symmetries suggests a complex interplay of phases that collectively enhance the material's ferroelectric properties, potentially offering new avenues for applications in electronic and optical devices. Notably, compared to 0.94NB1−xEuxTiO3‐0.06SrTiO3 with (x = 0), the coercive field (Ec) significantly improves, while remanent polarization decreases in the presence of Eu3+. The domain orientation, particularly in Stage‐C, demonstrates a pronounced scaling behavior, which can be attributed to the crystal field surrounding the Eu3+ ions. This interaction influences the material's domain dynamics, enhancing its electromechanical properties. As a result, both of these lead‐free ceramics exhibit considerable potential for future electroceramic applications, offering a promising alternative in environmentally sustainable technologies.