Lanthanide Halides Research Articles

Fully spin-polarized two dimensional polar semi-metallic phase in Eu substituted GdI2 monolayer

Abstract The coexistence of seemingly mutually exclusive properties such as ferromagnetism, ferroelectricity and metallicity in atomically thin materials is the requirement of the hour in electronics as the Moore’s law faces an impending end. Only a few 2D multiferroic materials have been predicted/realized so far. The polar metals with simultaneous presence of polarity and conductivity are also equally rare. Here, we predict, based on first-principles calculations that an Eu-substituted rare-earth halide GdI2 monolayer showcases ferromagnetism, ferroelasticity while being polar and a fully spin-polarized semi-metal at the same time. The ferroelasticity and polarity are shown to be coupled making it possible to switch the polar direction using external mechanical stress. Further, it is observed that an application of biaxial tensile strain of 5% causes the spin easy-axis to shift from out-of-plane to in-plane direction. Thus, spin easy axis gets coupled with the direction of polarization in the strained monolayer making the switching of magnetization also possible using external strain. Simultaneous coexistence and coupling of the ferroic orders in a metallic 2D material makes the Eu substituted GdI2 monolayer an incredibly rare material for nano-electronics and spintronics applications.

Enhanced Infrared Emission from Rare-Earth Double Perovskite Embedded in Fluoride Glass with Different B-Site Cation Structures for N2O Sensing in a Hydrogen Stream.

Rare-earth halide perovskites can lead to a distinctive infrared luminescence. However, achieving tunable infrared luminescence presents significant challenges. The leptons of their f-f ubiquitous forbidden ring influence the energy level splitting, and the substitution of atoms in perovskite by rare-earth ions also distorts the crystal structure. The research on achieving tunable mid-infrared emission by altering the crystal structure of rare-earth perovskites is limited. The crystal structure can be modified by changing the matrix B-site cation for a series of Cs2MIn1-xHoxCl6-ZBLAY (M = Na and Ag) rare-earth perovskites coated with a glass matrix that have been prepared. On this basis, we revealed the local electronic structure of Cs2MInCl6 (M = Na and Ag) perovskites and proposed an effective charge transfer strategy to achieve an efficient infrared emission of Ho3+ ions at 1.2 and 2.87 μm. The contribution of Na s and Na p is minor in Cs2NaIn1-xHoxCl6, which leads to poor interactions between Na+ and Cl- and promotes charge transfer of Ho3+-Cl- in the [HoCl6]3- octahedron. The charge transfer mechanism of Cs2NaInCl6:Ho3+-Cl- is validated by executing density functional theory calculations. Furthermore, a device that identifies N2O gas levels in hydrogen energy was built using the Cs2NaIn1-xHoxCl6-ZBLAY sample. These findings provide a new perspective on how to achieve effective infrared emission.

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material.

Exfoliation of graphite and the discovery of the unique properties of graphene─graphite's single layer─have raised significant attention to layered compounds as potential precursors to 2D materials with applications in optoelectronics, spintronics, sensors, and solar cells. In this work, a new orthorhombic polymorph of yttrium bromide, oC16-YBr3 was synthesized from yttrium and CBr4 in a laser-heated diamond anvil cell at 45 GPa and 3000 K. The structure of oC16-YBr3 was solved and refined using in situ synchrotron single-crystal X-ray diffraction. At high pressure, it can be described as a 3D framework of YBr9 polyhedra, but upon decompression below 15 GPa, the structure motif changes to layered, with layers comprising edge-sharing YBr8 polyhedra weakly bonded by van der Waals interactions. The layered oC16-YBr3 material can be recovered to ambient conditions, and according to Perdew-Burke-Ernzerhof-density functional theory calculations, it exhibits semiconductor properties with a band gap that is highly sensitive to pressure. This polymorph possesses a low exfoliation energy of 0.30 J/m2. Our results expand the list of layered trivalent rare-earth metal halides and provide insights into how high pressure alters their structural motifs and physical properties.

Multimode Luminescence with Temperature and Energy Level Synergistic Dependence in Rare Earth Halide DPs for Advanced Multifunctional Applications.

Rare-earth halide double perovskites (DPs) have attracted extensive attention due to their excellent optoelectronic performance. However, the correlation between luminescence performance, crystal structure, and temperature, as well as the inherent energy transfer mechanism, is not well understood. Herein, Lanthanide ions (Ln3+: Nd3+ or Dy3+) as the co-dopants are incorporated into Sb3+ doped Cs2NaYbCl6 DPs to construct energy transfer (ET) models to reveal the effects of temperature and energy levels of rare earth on luminescence and ET. The different excited state structures of Sb3+-Ln3+ doped Cs2NaYbCl6 DPs at different temperatures and relative positions of energy levels of rare earth synergistically determine the physical processes of luminescence. These multi-mode luminescent materials exhibit good performance in anti-counterfeiting, NIR imaging, and temperature sensing. This work provides new physical insights into the effects of temperature and energy levels of rare earth on the energy transfer mechanism and related photophysical process.

A dual-functional rare earth halide additive for high-performance aqueous zinc ion batteries

Aqueous zinc ion batteries have received much attention due to their high theoretical capacity, inherent safety, and low cost. However, the growth of zinc dendrites and side reactions hinder its practical application. In this study, a rare-earth metal salt, europium chloride (EuCl3), is used as a new electrolyte additive to regulate the uniform deposition of zinc and inhibit the interfacial side reactions. The EuCl3 additive benefits for preferentially Zn2+ deposition along the (002) crystal plane, as well as suppress the hydrogen evolution reaction (HER) at electrode-electrolyte interface. As a result, the capacity retention of the Zn//NaV3O8 full cell assembled with the modified electrolyte much better than that without additives, showing a long-term cycling life and high coulombic efficiency at a current density of 10 A g−1. This new dual-functional rare earth halide additive strategy provides great potential for the development of practical aqueous zinc ion batteries and other battery systems.

High thermoelectric properties in polycrystalline SnSe materials realized by rare earth halide Co-doping

SnSe materials have garnered significant interest due to the intrinsic low thermal conductivity. However, its limited electrical conductivity hinders their practical implementation. This study achieved a high ZT value of 1.40 at 773 K in the samples of n-type polycrystalline SnSe0.95 + x wt% SmCl3 + y wt% ErCl3 (x = 0, 0.75, 1.0, 1.25, and 1.5; y = 0, 0.0675, 0.125, and 0.25) since (SmCl3, ErCl3) co-doping decoupled the electrical-thermal transport properties. First, the released electron carrier concentration due to SmCl3 doping enhanced the electrical transport properties. The SnSe0.95 + 1.25 wt% SmCl3 sample exhibited a high power factor of 563 μWm−1K−2 at 773 K. Then, the lattice thermal conductivity markedly decreased with further ErCl3 doping due to the high-density dislocations and coherent boundary, resulting in effective the phonon scattering. Additionally, the special microtopography was conducive to the decreased lattice thermal conductivity. Therefore, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample achieved a low lattice thermal conductivity value of 0.28 Wm−1K−1 at 773 K. Simultaneously, the (SmCl3, ErCl3) co-doped samples maintained the electrical transport properties than the SmCl3-doped samples. Consequently, the SnSe0.95 + 1.25 wt% SmCl3 + 0.125 wt% ErCl3 sample obtained a peak ZT value of 1.40 at 773 K and a competitive average ZT value of 0.37 from 323 to 773 K, and a theoretically calculated conversion efficiency reached 7.2%, which can be applied in the deep space for power generation. This strategy can be utilized to optimize the thermoelectric performance of other thermoelectrical material systems.

First principle examination of two dimensional rare-earth metal germanide halides Y2GeX2 (X = Cl, Br, I) for thermoelectric applications

In the present work electronic, structural and thermoelectric properties of newly designed layered rare-earth metal germanide halides such as Y2GeX2 (X = Cl, Br, I) are investigated. These materials are indirect band gap semiconductors with narrow band gap 0.30 eV for Y2GeCl2,0.36 eV for Y2 GeBr2, and 0.41 eV for Y2GeI2 respectively. First principles method along with Boltzmann transport equations (BTE) is utilized together to analyse the thermoelectric properties. These materials are dynamically and mechanically stable. Thermoelectric coefficients such as electrical conductivity, seebeck coefficient and thermal conductivity are computed and put together to ultimately get the Figure of merit (ZT). Y2GeI2 has highest figure of merit (ZT) of 0.42 with Seebeck coefficient 532.12 VK−1, electrical conductivity 8.6 ×105Sm−1 and has lowest lattice thermal conductivity value of 5.55 Wm−1K−1 among three materials, which is necessary to achieve high figure of merit. The computed value of Figure of merit 0.07, 0.22 and 0.42 for Y2GeCl2, Y2GeBr2 and Y2GeI2 accordingly, shows that these materials can be considered as good candidates for energy harvesting in thermoelectric applications.

Large effective magnetic fields from chiral phonons in rare-earth halides.

Time-reversal symmetry (TRS) is pivotal for materials' optical, magnetic, topological, and transport properties. Chiral phonons, characterized by atoms rotating unidirectionally around their equilibrium positions, generate dynamic lattice structures that break TRS. Here, we report that coherent chiral phonons, driven by circularly polarized terahertz light pulses, polarize the paramagnetic spins in cerium fluoride in a manner similar to that of a quasi-static magnetic field on the order of 1 tesla. Through time-resolved Faraday rotation and Kerr ellipticity, we found that the transient magnetization is only excited by pulses resonant with phonons, proportional to the angular momentum of the phonons, and growing with magnetic susceptibility at cryogenic temperatures. The observation quantitatively agrees with our spin-phonon coupling model and may enable new routes to investigating ultrafast magnetism, energy-efficient spintronics, and nonequilibrium phases of matter with broken TRS.

Two-dimensional rare-earth halide based single-phase triferroic

Two-dimensional rare-earth halide based single-phase triferroic

Self-calibrated multi-mode optical thermometry in up-converting phosphor Cs2NaErCl6: Yb3+

With the development of temperature measurement technology, people put forward higher requirements for the accuracy and precision of temperature measurement. However, most of the current luminescent thermometers use a single optical signal for temperature detection, which has a certain range of temperature insensitivity, resulting in inaccurate temperature measurement. Here, an all-inorganic rare-earth halide double perovskite Cs2NaErCl6: Yb3+ (CNEC: Yb3+) phosphor was synthesized, which not only expressed triple-mode thermometric properties based on thermally coupled levels (TCLs), non-thermally coupled levels (N-TCLs) and lifetime (FL), but also capable of providing self-referencing and high-sensitivity temperature measurements under excitation at 980 nm. Benefiting from the low phonon energy of the matrix, high doping concentration and the excellent internal up-conversion quantum efficiency (UCQY) about 6.52% of optimal composition CNEC: 40%Yb3+, all modes exhibit superior sensitivities, reversibility and thermal resolution under 980 nm irradiation. In addition, a flexible thin film thermometer composed of CNEC: 40%Yb3+ was prepared to realized multi-mode thermal monitoring of local hot spots of electronic components. The excellent three-mode temperature measurement results indicated that CNEC: Yb3+ phosphors have great potential in temperature sensing.

Efficient passivation of porous silicon with LaF3 by deep eutectic solvent based novel chemical route

Sensors and optoelectronic devices frequently employ rare-earth halides like lanthanum fluoride (LaF3). This article presents the investigation on the passivation of pore walls of porous silicon (PS) with LaF3 using a deep eutectic solvent (DES) based novel chemical route. The DES, called ethaline, a 1:2 M solution of choline chloride and ethylene glycol, has been used as the solvent of LaF3. Spin-coating deposits the precursor solution on the pore wall of PS, and subsequent annealing evaporates the DES leaving LaF3 on the pore wall as a passivating layer. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses indicated an almost stoichiometric and highly crystalline nature of deposited LaF3. The surface of the LaF3 was uniform and crack-free as revealed by scanning electron microscopy (SEM). The photoluminescence (PL) behavior of the LaF3-passivated PS structures further supported the passivation of PS. Compared to the freshly prepared PS without LaF3 passivation LaF3-passivated PS structure exhibits stable photoluminescence. The investigations show that the facile DES-based chemical route with the simple spin-coating technique can provide good passivation of PS by the LaF3 layer that may enable LaF3-passivated PS to be an ideal candidate for low-cost electronic and optoelectronic devices.

Structural Evolution in a Series of Isomorphous Rare Earth Compounds as Response of Lanthanide Contraction

The structural parameters of the rare-earth diacetate halide trihydrates, RE(OAc)2Hal·3H2O with RE = Ce − (Pm) − Lu and Hal = Cl, Br, have been determined by low temperature, high-resolution SCXRD in order to examine the effect of lanthanide contraction on the coordination geometry in this series of isomorphous compounds consisting of cationic, acetate-bridged, non-linear, one-dimensional coordination polymers of composition [RE(H2O)3(OAc)2]+ and laterally hydrogen bonded halide ions, Hal−. Although the shrinkage of the unit cell volume follows lanthanide contraction very well over the complete range of investigated RE elements, many other parameters (i.e., lattice constants, angles and distances in the RE··· RE alignment, RE-O bond lengths, etc.) exhibit a more complex response on lanthanide contraction often expressed by sigmoid curves that can be ascribed to a continuous transition from CN9 (RE = Ce) to CN8 (RE = Lu) as one acetate group loses the chelate function, an effect accompanied by significant structural changes of the carboxylate group. Therefore, data are best analyzed by use of two subsets represented by the two different structure types of Ce and Lu, the structural features of which change with decreasing/increasing the size of RE3+, up to the borderline between both subsets.

Vacuum-deposited Rb3CeI6 for deep-blue-light-emitting diodes.

Recently, perovskite light-emitting diodes (PeLEDs) have exhibited outstanding performance in next-generation high-definition display applications. However, compared with green and red PeLEDs, the development of efficient and stable blue PeLEDs to meet the requirement for a wide color gamut has been a challenge. Herein, we vacuum thermally deposited a film of the lead-free rare earth halide Rb3CeI6, which shows deep blue emission with peaks at 427 nm and 468 nm. Due to the parity-allowed 5d-4f transition of Ce(III), the excited-state lifetime is as short as 22.3 ns (427 nm) and 25 ns (468 nm), respectively. The photoluminescence quantum yield (PLQY) is optimized to 51% by regulating the nucleation and growth of Rb3CeI6 grains. In a prototype rare earth light-emitting diode (ReLED) device, a thin insulating Al2O3 layer (5 nm) is inserted between the electron transport layer (ETL) and the emitting layer (EML, Rb3CeI6) to balance the carriers and reduce the dark current. The device shows a maximum luminance and EQE of 98 cd m-2 and 0.67%, respectively, and the electroluminescence (EL) spectrum maintains stability with changes in the operating voltage. In addition, the corresponding CIE coordinate is (0.15, 0.06), which closely matches the Rec. 2020 standard (0.131, 0.046).

Rare earth halide double perovskites for high-performance resistive random access memory

We report the resistive memory devices based on rare earth halide double perovskite Cs2AgEuBr6 films which demonstrate a typical random-access memory (ReRAM) behavior with high ON/OFF ratio and long retention time.

Molecular Dynamics and Free Energy Calculations of Dicyclohexano-18-crown-6 Diastereoisomers with Sm2+, Eu2+, Dy2+, Yb2+, Cf2+, and Three Halide Salts in Tetrahydrofuran and Acetonitrile Using the AMOEBA Force Field.

With the continual development of lanthanides (Ln) in current technological devices, an efficient separation process is needed that can recover greater amounts of these rare elements. Dicyclohexano-18-crown-6 (DCH18C6) is a crown ether that may be a promising candidate for Ln separation, but additional research is required. As such, molecular dynamics (MD) simulations have been performed on four divalent lanthanide halide salts (Sm2+, Eu2+, Dy2+, and Yb2+) and one divalent actinide halide salt (Cf2+) bound to three diastereoisomers of DCH18C6. Dy2+, Yb2+, Cf2+, DCH18C6, and tetrahydrofuran (THF) solvent were parameterized for the AMOEBA polarizable force field for the first time, whereas existing parameters for Sm2+ and Eu2+ were utilized from our previous efforts. A coordination number (CN) of six for Ln2+/An2+-O solvated in THF indicated that the cations interacted almost entirely with the oxygens of the polyether ring. A CN of one for Ln2+/An2+-N solvated in acetonitrile for systems containing iodide suggested that the N atom of acetonitrile was competitive with I- for cation interactions. Fluctuation between five and six CNs for Dy2+ and Yb2+ suggested that although the cations remained in the polyether ring, the size of the ring may not be an ideal fit as these cations possess comparatively smaller ionic radii. Gibbs binding free energies of Sm2+ in all DCH18C6 diastereoisomers solvated in THF were calculated. The binding free energy of the cis-syn-cis diastereoisomer was the most favorable, followed by cis-anti-cis, and then trans-anti-trans. Finally, two major types of conformation were observed for each diastereoisomer that were related to the electrostatic interactions and charge density of the cations.

Ultrafast and Multicolor Luminescence Switching in a Lanthanide-Based Hydrochromic Perovskite.

Hydrochromic materials characterized by noticeable color change upon water exposure have attracted pervasive attention for their frontier applications in sensing and information technologies. However, existing hydrochromic materials typically suffer from a slow hydrochromic response as well as limited stability and color tunability. This work describes a novel hydrochromic perovskite crystal composed of zero-dimensional Cs3TbF6:Eu3+, which displays switchable luminescence due to the constituent Tb3+ and Eu3+ ions. Mechanistic investigation reveals that the hydrochromic property stems from a water-induced phase transformation into a one-dimensional structure through a CsF-stripping process. The phase transformation triggers energy coupling between Tb3+ and Eu3+ ions in adjacent lanthanide halide polyhedra, resulting in an emission color change from green to orange. Notably, the phase transformation is ultrafast (20 ms) and reversible, and the emission color in each phase can be fine-tuned by controlling the Eu3+ doping concentration along with Y3+ co-doping. The advances in these hydrochromic luminescent materials offer exciting opportunities for information security and data storage.

Study on the Thermoelectric Properties of n-Type Polycrystalline SnSe by CeCl3 Doping

SnSe is a promising medium-temperature thermoelectric material due to its extremely low thermal conductivity and tunable electronic transport properties. In this work, n-type SnSe0.95 polycrystals doped with CeCl3 are synthesized by a melting method combined with a spark plasma sintering (SPS) process. The samples have highly textured structures and anisotropic thermoelectric properties. CeCl3 doping has a favorable effect on the electronic transport above 473 K, which may benefit from the excitation of the introduced impurity energy level. Moreover, the thermal conductivity is significantly reduced due to the phonon scattering by point defects. Finally, a peak ZT value of 1.17 is obtained at 773 K in SnSe0.95–0.5 mol % CeCl3, which paves the way for improving the thermoelectric performance of n-type SnSe via rare-earth halide doping.

Enhanced thermoelectric performance of n-type polycrystalline SnSe via NdCl3 doping

A series of n-type polycrystalline SnSe0.95 - xmol% NdCl3 samples were synthesized using the melting method combined with spark plasma sintering (SPS). Doping NdCl3 significantly improves the electrical conductivity and suppresses the deterioration of the Seebeck coefficient after thermal excitation, which leads to significantly higher power factors than SnSe0.95. In addition, excessive doping of NdCl3 not only introduces a large number of point defects but also produces NdCl3 precipitates, which largely enhances the phonon scattering and significantly reduces the thermal conductivity. As a result, a maximum ZT value of 1.3 at 773 K has been obtained in SnSe0.95 - 1.5 mol% NdCl3 sample, indicating that the doping of rare earth halides can effectively enhance the thermoelectric performance of n-type SnSe0.95 by simultaneously improving the power factor and reducing the lattice thermal conductivity.

Crystal growth and luminescence characterizations of halide scintillators K2LaBr5:Eu2+

Recent researches have shown that Eu2+ ion heterovalently doped rare earth halide scintillators attract the attention of researchers. In this paper, the transparent K2LaBr5 scintillation crystals of centimeter size doped with heterovalent Eu2+ were successfully grow by the vertical Bridgman technique. X-ray powder diffraction analysis shows that the crystal has an orthonormal structure with space group Pnma(62). A small amount of Eu2+ doping does not change the internal structure of the crystal.The transmittance, the UV–visible excited spectrum and emission spectrum, X-ray excited luminescence spectrum, Photoluminescence decay time and scintillation pulse decay time have been measured at room temperature. The results show that the crystal has strong luminescence intensity, and the maximum emission peak is about 430 nm. The photoluminescence decay time of K2LaBr5:xmol.%Eu2+(x = 0.5, 1, 2) are 5.56 μs, 5.67 μs and 7.03 μs, respectively. The decay time of K2LaBr5:Eu2+ crystal under 137Cs 662 keV radiation is nanosecond, indicating that the K2LaBr5:Eu2+ crystal has fast decay characteristics and excellent time resolution performance.

Enhancement of Superionic Conductivity by Halide Substitution in Strongly Stacking Faulted Li3HoBr6–xIx Phases

Ternary lithium halide-based solid electrolytes have attracted broad scientific interest due to their high ionic conductivities in conjunction with good electrochemical stabilities against high-voltage cathode materials. Here, we analyze the structure of the rare earth halide solid solution series Li3HoBr6–xIx and quantify structural defects such as intralayer cation disorder and stacking faults. Almost all members of the solid solution series show strong stacking fault disorder, whereas the intralayer cation disorder systematically increases with increasing iodide content. The substitution of bromide by iodide in Li3HoBr6–xIx leads to an increasing lattice softness and therefore to a higher ionic conductivity and to a lower activation energy. This is counteracted by the increased cation disorder, which also has a strong influence on the ionic conductivity of the solid solution series. Thus, a decrease in ionic conductivity by one order of magnitude is observed when the iodine content exceeds an optimum value. Stacking faults on the other hand do not have a significant impact on the ionic conductivity as the connectivity between neighboring lithium halide octahedra and hence the energy landscape of their migration pathways is not affected for equivalent stacking vectors. The competing factors above give rise to an optimum ionic conductivity at x ≈ 3 with 2.7 × 10–3 S cm–1 at 20 °C and an activation energy of 0.21 eV. While thermal annealing reduces the structural disorder of Li3HoBr6–xIx, the self-healing properties are significantly impeded by mechanical sample treatment, demonstrating the complex interplay between thermal and mechanical effects on the microstructure and, hence, ionic conductivity of layered superionic conductors.