Rare Earth Sulfides Research Articles

Effect of rare earth lanthanum on non-metallic inclusions in Fe-Mn-C-Al alloy

ABSTRACT The effect of La addition on non-metallic inclusions in Fe-Mn-C-Al alloy was studied by adding different contents of rare earth lanthanum (La). Among the studied samples, the one with La addition of 0.0043 wt.% demonstrates the best inclusion characteristics. In this sample, the average size of inclusions measures at 1.16 μm. Compared with the sample without the addition of rare earth La, the size and area density of inclusions decrease, while the quantity density increases. With the increase of rare earth addition, inclusions in the samples showed a gradually increasing trend in inclusions size and area density, but both were lower than those in the sample without the addition of rare earth La. Through scanning electron microscopy observation, as the amount of rare earth La added increases, MnS inclusions are gradually replaced by rare earth sulfides. Based on classical thermodynamics and Factage thermodynamic software, the modification law of inclusions after La addition was calculated. Combining theoretical calculations and scanning electron microscopy experimental observations, it was found that the main transformation path of non-metallic inclusions in La treated alloy is: Al2O3 → LaAl11O18 → LaAlO3, MnS → MnS + La2S3 → La2S3 + LaS.

Optical properties of Er3+: NaYbS2 nanocrystals in oxysulfide glass-ceramics

Ternary alkali rare-earth sulfide (ALnS2) has excellent luminescent performance, showing promising application prospects in the field of light-emitting diodes and optical communication. However, the poor chemical stability of ALnS2 makes it difficult to meet the needs of practical application. Herein, we develop a new type of oxysulfide glass-ceramics containing NaYbS2 nanocrystals (NCs) through conventional melt-quenching and subsequent heat treatment. NaYbS2 NCs and Er3+: NaYbS2 NCs are successfully precipitated in oxysulfide glass-ceramics, and their optical properties are studied. NaYbS2 NCs in glass-ceramics exhibit strong concentration quenching with the increase in heat-treatment temperature. Incorporation of Er3+ ions into NaYbS2 NCs results in efficient energy transfer (ET) from Yb3+ ions to Er3+ ions with efficiency as high as 90.9%.

LiLnGeS4 (Ln=La-Nd): Designing High Performance Infrared Nonlinear Optical Sulfides through "Band Reformation of AGS".

AgGaS2 (AGS) is the most commonly used commercial infrared nonlinear optical (IR NLO) material. However, AGS has a narrow band gap (Eg=2.58 eV) and a low laser-induced damage threshold (LIDT), primarily attributed to its mobile liquid-like Ag+ constituent and the unstable Ag-S chemical bond. Herein, we propose a "band reformation of AGS" strategy, which leads to the successful syntheses of four lanthanide sulfides, LiLnGeS4 (Ln=La-Nd), crystalizing in an asymmetric Ama2 structure. LiLaGeS4 demonstrates that eliminating the presence of Ag-4d band increases the Eg to 3.32 eV and enhances the LIDT (14-29×AGS, measured by both powder and single crystal); while increasing the nonbonding density of states of the S-3p band enhances the 2nd-nonlinear optical coefficient (1.06×AGS). Besides, the bond length discrepancy between [LiS4], [GeS4] and [LaS8] units leads to a moderate birefringence (Δn=0.052). Such a unique structure further results in extremely small thermal expansion with αL=0.41-1.74×10-5 K-1, along different crystallographic axes. Our theoretical studies indicate that the synergy of the structure building units contribute to the second harmonic generation performance. These results suggest that the "band reformation of AGS" strategy provides effective guidance to discover new NLO crystals with optimized performance.

LiLnGeS4 (Ln=La−Nd): Designing High Performance Infrared Nonlinear Optical Sulfides through “Band Reformation of AGS”

AbstractAgGaS2 (AGS) is the most commonly used commercial infrared nonlinear optical (IR NLO) material. However, AGS has a narrow band gap (Eg=2.58 eV) and a low laser‐induced damage threshold (LIDT), primarily attributed to its mobile liquid‐like Ag+ constituent and the unstable Ag−S chemical bond. Herein, we propose a “band reformation of AGS” strategy, which leads to the successful syntheses of four lanthanide sulfides, LiLnGeS4 (Ln=La−Nd), crystalizing in an asymmetric Ama2 structure. LiLaGeS4 demonstrates that eliminating the presence of Ag‐4d band increases the Eg to 3.32 eV and enhances the LIDT (14–29×AGS, measured by both powder and single crystal); while increasing the nonbonding density of states of the S‐3p band enhances the 2nd‐nonlinear optical coefficient (1.06×AGS). Besides, the bond length discrepancy between [LiS4], [GeS4] and [LaS8] units leads to a moderate birefringence (Δn=0.052). Such a unique structure further results in extremely small thermal expansion with αL=0.41–1.74×10−5 K−1, along different crystallographic axes. Our theoretical studies indicate that the synergy of the structure building units contribute to the second harmonic generation performance. These results suggest that the “band reformation of AGS” strategy provides effective guidance to discover new NLO crystals with optimized performance.

Construction of heterojunction based on Nd2S3 and tin dioxide for rapid detection of ethanol

The gas-sensing properties of Nd2S3 have not been previously explored. In this study, a novel composite material comprising rare-earth metal sulfide (Nd2S3) and metal oxide (SnO2) was successfully prepared using a two-step hydrothermal method for the rapid detection of ethanol. Characterization results revealed that the morphology and specific surface area of Nd2S3-SnO2 remained largely unchanged after composite formation. However, the built-in electric field established between Nd2S3 and SnO2 significantly enhanced carrier transport and separation. Additionally, the introduction of extra oxygen vacancies increased the content of chemisorbed oxygen, providing more active sites for ethanol molecules, thereby improving the gas-sensing performance. The Nd2S3-SnO2 sensor demonstrated extremely high detection accuracy (R2=0.9965) over the 20–300 ppm ethanol concentration range, with response/recovery time of 8/274 s at 100 ppm ethanol concentration and response value of 93. It also possesses excellent selectivity to ethanol, long-term stability and reversibility. This work represents a preliminary exploration of the gas-sensing properties of Nd2S3 and its underlying mechanisms through the construction of a heterojunction structure between metal sulfide and metal oxide.

Microbial green synthesis of luminescent terbium sulfide nanoparticles using E. Coli: a rare earth element detoxification mechanism

BackgroundRare-earth sulfide nanoparticles (NPs) could harness the optical and magnetic features of rare-earth ions for applications in nanotechnology. However, reports of their synthesis are scarce and typically require high temperatures and long synthesis times.ResultsHere we present a biosynthesis of terbium sulfide (TbS) NPs using microorganisms, identifying conditions that allow Escherichia coli to extracellularly produce TbS NPs in aqueous media at 37 °C by controlling cellular sulfur metabolism to produce a high concentration of sulfide ions. Electron microscopy revealed ultrasmall spherical NPs with a mean diameter of 4.1 ± 1.3 nm. Electron diffraction indicated a high degree of crystallinity, while elemental mapping confirmed colocalization of terbium and sulfur. The NPs exhibit characteristic absorbance and luminescence of terbium, with downshifting quantum yield (QY) reaching 28.3% and an emission lifetime of ~ 2 ms.ConclusionsThis high QY and long emission lifetime is unusual in a neat rare-earth compound; it is typically associated with rare-earth ions doped into another crystalline lattice to avoid non-radiative cross relaxation. This suggests a reduced role of nonradiative processes in these terbium-based NPs. This is, to our knowledge, the first report revealing the advantage of biosynthesis over chemical synthesis for Rare Earth Element (REE) based NPs, opening routes to new REE-based nanocrystals.

A Rare Earth Chalcogenide Nonlinear Optical Crystal KLaGeS4: Achieving Good Balance among Band Gap, Second Harmonic Generation Effect, and Birefringence.

Midinfrared nonlinear optical (NLO) rare earth chalcogenides have attracted extensive research interest in recent several decades. Employing charge-transfer engineering strategy in the early stage, rigid tetrahedral [GeS4] was introduced into rare-earth sulfides to synthesize KYGeS4, which had an enlarged band gap while maintaining a strong second harmonic generation (SHG) effect. Based on KYGeS4, La was equivalently substituted to successfully synthesize KLaGeS4 with a stronger SHG effect (dij = 1.2 × AgGaS2) and lower cost. Meanwhile, a larger band gap (Eg = 3.34 eV) was retained and realized phase matching (Δn = 0.098 @ 1064 nm). KLaGeS4 enabled an effective balance among band gap, SHG effect, and birefringence, making it a promising candidate for infrared NLO optical materials among various rare-earth sulfides.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8).

The ternary rare-earth sulfides RE2SnS5 (RE = La-Nd) and the partial solid solutions RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La2SnS5-type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing SnCh6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE2Sn(S1-xSex)5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE2SnSe5 do not form. Solid-state 119Sn NMR spectra confirmed the nonrandom distribution of SnS6-nSen local environments, which could be resolved into individual resonances. The Raman spectra of RE2SnS5 compounds show an intense peak at 307-320 cm-1 assigned to a symmetric A1g mode, which is dominated by Sn-S bonds; the Raman peak intensities varied with Se substitution in La2Sn(S1-xSex)5. Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE2SnS5 (0.7 eV) but they gradually decrease with greater Se substitution in RE2Sn(S1-xSex)5 (0.7-0.4 eV).

Yellow rare earth sulfide powders with near‐infrared reflectance and spectral modulation for energy‐saving applications

AbstractRadiative cooling pigments offer new opportunities for sustainable carbon neutrality as zero‐energy and zero‐pollution functional materials. However, it is a challenge to prepare inorganic yellow pigments simultaneously with environmentally friendly, high color value, and weather resistance. In this study, a series of alkali metal‐doped γ‐Sm2S3 yellow pigments with near‐infrared reflectance were synthesized. The doping of alkali metal ions reduced synthesis temperature of Sm2S3 from 1300°C to 1000°C. The change in energy band structure induced by alkali metal doping allows the products to exhibit modifiable colors. Typical γ‐[Na]‐Sm2S3 pigment powders have a high near‐infrared reflectance and impressive colors (b* = 78.6, C* = 77.6). Furthermore, colored films made by prepared yellow powders with polyvinylidene fluoride in certain ratios had high near‐infrared reflectance and excellent environmental weathering, resulting in an effective cooling of 4–8°C in outdoor experiments. This work expands the range of options for energy‐efficient building and yellow colorant.

Promoting thermal stability and acid resistance of rare earth sulfide powders by coating ZnO and SiO2 double shells

AbstractAs an environment‐friendly powder with good coloring performance, rare earth sulfide is one kind of the important choices to replace cadmium and lead colorants. In particular, γ‐Ce2S3 belongs to rare earth sesquisulfide, which has a bright red color. However, the uncoated γ‐Ce2S3 is easy to decompose and release H2S in a humid or acidic environment, and its air thermal stability is limited to 350°C. In this work, γ‐Ce2S3 powders coated with zinc oxide were prepared by heterogeneous precipitation method, and a dense protective layer was formed by ZnO to improve chemical and thermal stability. Moreover, silicon dioxide was deposited on the surface of the zinc oxide coating using the microemulsion process to strengthen the powder's acid resistance. The double shells structure greatly promoted thermal stability and acid resistance of γ‐Ce2S3 powders. The results showed that rare earth sulfide powders with double shells have good stability for coloring applications.

Ion Substitution Strategy toward Spectral Tunability of Environmentally Friendly Rare Earth Sulfide Lattices for Radiative Cooling

Ion Substitution Strategy toward Spectral Tunability of Environmentally Friendly Rare Earth Sulfide Lattices for Radiative Cooling

A series of new rare-earth sulfide borates RE3S3BO3 (RE = Nd, Tb, Dy): Syntheses, structures and optical properties

Exploration of new compounds belonging to unusual families is always attractive for the everlasting development of material science. Here, three isomorphic rare-earth sulfide borates RE3S3BO3 (RE = Nd, Tb, Dy) have been obtained via a facile metal oxide-boron-sulfur solid-state routine. Their centrosymmetric triclinic structures feature 3D framework built by three types of REOxSy units, viz. REOS6, REO4S3, and REO3S6. Their structural relationship with similar phases and lanthanide contraction rule are discussed. Their optical band gaps are measured to be 2.59–2.70 eV, and the corresponding theoretical calculations are also performed. This work enriches the rarely studied chalcogenide borate system and is conducive to discovering more inorganic materials.

Effect of sodium ions doping on structure and spectral properties of γ-Ce2S3 microcrystals

Rare earth sulfides are environmentally friendly and have excellent physical optoelectronic properties and coloring applications. In particular, red γ-Ce2S3 is an important and popular inorganic optical functional material. However, it has become crucial to improve the production efficiency of γ-Ce2S3 and its color performance and stability. By adding ammonium thiocyanate to the precursor, eco-friendly γ-Ce2S3 with excellent color performance was produced in this study. In addition, the effect of different amounts of Na+ doping on the final product's purity and the effect of chroma value were systematically investigated. Results show that an increase in Na+ can effectively lower the synthesis temperature of γ-Ce2S3, improve production efficiency, and optimize color performance prior to saturation. Finally, using density functional theory, the influence of the vacancy structure of γ-Ce2S3 and the change of energy band after the addition of Na+ were calculated, and a detailed experimental characterization in conjunction with density functional theory calculation thoroughly explained the significance of ion doping for reaction synthesis.

Study of Magnetic, Optical, Electronic and Thermodynamic Effects in Thallium Rare Earth Disulphides (TlRES2, RE= Tb- Er)

In the present research work, we have investigated density of electronic states, electronic band structure, magnetic structure, optical spectra and temperature dependent thermodynamic characteristics of thallium rare earth sulphides, TlRES2 (RE: Tb-Er) using FP-LAPW method and PBE-GGA exchange correlation within DFT. The electronic structure pointed out that TlRES2 compounds show half metallic character. The magnetic moment and spin polarization calculations prove that TlRES2 are fully spin polarized compounds with ferromagnetic nature. Optical spectra show that intraband transitions occur in infrared (IR) regime due to half metallic character of TlRES2 and behave as opaque in ultraviolet (UV) region. High refractive index in IR regime also show metallic character and high peak in UV regime show slow propagation of light in UV regime. The reflection coefficient is found maximum (~50–60%) in UV regime. Greater energy loss has been seen on the higher energy side, which corresponds to the stimulation of plasmons by electrons moving through the compounds. Plasma resonances lead to the frequent peaks at ~ 6.0 eV, 11.0 eV, and 12.0 eV. According to calculations made using the quasi-harmonic Debye model, TlRES2 compounds are dimensionally less stable (i.e., much hard), have poor thermal conductivity, and experience faster-than-average disorder with increasing the temperature.

The problem of oxide admixtures in zinc sulfide as a material for infrared optics (a review)

The paper reports on the main physicochemical properties of zinc sulfide (ZnS) and the features of its application in optics, optoelectronics, and semiconductor technology, as well as the main synthesis methods (synthesis in a solution, self-propagating high-temperature synthesis, and chemical vapor deposition). The harmful effect of the ZnO admixture on the optical and operational properties of zinc sulfide as a starting material for optical ceramics and in a thin film coating is shown. Possible ways of zinc oxide entering the base material during synthesis, storage in air or subsequent heat treatment are considered. The possibility of detecting and estimating the content of oxide admixture (ZnO) in ZnS by methods of substantial chemical analysis has been established. For the first time, approaches were proposed and implemented aimed at weakening the harmful effect of oxide admixtures by binding them with the help of lanthanide sulfides and sulfofluorides, followed by the formation of lanthanide oxosulfides by exchange reactions. The use of the addition of boron oxide (B2O3) with the formation of complex compounds with significantly lower chemical activity and volatility compared to ZnO is considered more promising. The method developed by the authors implies the complete removal of the ZnO impurity by heat treatment of the material with a sulfurizing agent, Sb2S3, the excess of which is removed by heat treatment in a vacuum. This method seems to be more labor-intensive, but more attractive for consumers of zinc sulfide as a material for interference optics.

Modulating interfacial defects for dual-enhancing chromaticity and stability of cerium sulfide

To obtain rare earth sulfides with satisfied chromaticity and stability for diverse applications in the field of pigment, a harnessed synthetic molecular strategy for in-situ growth of CePO4 as an interlayer between core Ce2S3 substrate and the outer SiO2 layer is proposed. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), electron paramagnetic resonance (EPR), and Raman analysis reveal that the transition layer CePO4 significantly reduces the lattice spacing differences and reduces the oxygen activity on the interface, resulting in excellent chromaticity (L∗ ​= ​51.9, a∗ ​= ​45.0, b∗ ​= ​30.0) and stability for γ-Ce2S3@CePO4@SiO2. These insights will advance the fundamental knowledge of core-shell crystal engineering and enable new ways to promote the application of rare earth sulfides.

Template-directed shape control synthesis of rare earth sulfide for oxygen evolution reaction

Electrochemical water splitting for the generation of hydrogen and oxygen has great importance for energy storage and conversion technologies. The availability of an efficient electrocatalysts for oxygen evolution reactions to produce molecular oxygen is very important for development renewable energy technologies. The design and successfully development of an efficient electrocatalyst with controlled surface morphologies are still great challenge towards oxygen evolution reaction (OER). Till now various transition metal-based electrocatalysts have been developed with remarkable catalytic activity. In present study we have developed rare earth sulfides La2S3 and Sm2S3 using template assisted hydrothermal method and applied as catalyst for OER. The developed catalysts have been characterized by different techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), furrier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption isotherm (BET) and energy dispersive spectroscopy (EDS) with qualitative and quantitative estimation. The developed catalysts La2S3 and Sm2S3 offered overpotential 239 and 343 mV vs. RHE, respectively, to attain current density 10 mA cm−2. The efficient tube shaped catalyst La2S3 is better than Sm2S3 and exhibited faster kinetics with small Tafel slope 59.32 mV decade−1.

Ab initio composite strategies and multireference approaches for lanthanide sulfides and selenides.

The f-block ab initio correlation consistent composite approach was used to predict the dissociation energies of lanthanide sulfides and selenides. Geometry optimizations were carried out using density functional theory and coupled cluster singles, doubles, and perturbative triples with one- and two-component Hamiltonians. For the two-component calculations, relativistic effects were accounted for by utilizing a third-order Douglas-Kroll-Hess Hamiltonian. Spin-orbit coupling was addressed with the Breit-Pauli Hamiltonian within a multireference configuration interaction approach. The state averaged complete active space self-consistent field wavefunctions obtained for the spin-orbit coupling energies were used to assign the ground states of diatomics, and several diagnostics were used to ascertain the multireference character of the molecules.

Homovalent cation substitutions leading to new lithium-containing La3CuSiS7 family members having chiral, uniaxial structures and exhibiting second- and third-harmonic generation

Eighteen isotypic, lithium-containing rare-earth sulfides, crystallizing in the chiral, polar, and noncentrosymmetric space group P63 with the La3CuSiS7-structure type have been prepared via direct combination of the elements or binary sulfides; nine of these compounds are reported for the first time. The structures of these compounds, with the formulae Ln3LiTS7 (Ln = La, Ce, Pr, Nd, Sm, Gd, and Dy for T = Si or Ge; Ln = La, Ce, Pr, and Nd for T = Sn), were determined by single crystal X-ray diffraction. According to X-ray powder diffraction data, the Ln3LiTS7 compounds are the major phase of the reaction products. All of the compounds are semiconductors with optical bandgaps spanning nearly the entire visible region. The Si- and Ge-containing analogs show high thermal stability,> 1000 °C, while the Sn-containing compounds melt in the vicinity of ~740 °C. The compounds show potentially broad regions of optical transparency in the infrared regime. Calculated bond valence sums (BVSs) and global instability index (G) values confirm the Ln3+ oxidation state and stable crystal structures with reasonable strain, respectively. Ce3LiGeS7 and Ce3LiSnS7 display non-phase-matching but significant second-harmonic generation responses with χ2 values of 21 ± 1 and 28 ± 1 pm/V, respectively at λ = 1.8 µm. The laser-induced damage threshold values for Ce3LiGeS7 and Ce3LiSnS7 are> 3 × commercial AgGaSe2, for picosecond pulses at λ = 1.064 µm. These two compounds also exhibit moderate third-harmonic generation responses. Additionally, crystal-chemical correlations are discussed.

Effect of rare earth elements on magnetic properties of non-oriented electrical steels

The effect of rare earth elements (REMs) on the magnetic properties of non-oriented electrical steels was studied using industrial trials. The variation of the magnetic properties was discussed in terms of the effect of inclusions, precipitates, grain size, and textures in the steel with and without REMs. Inclusions of MgO·Al2O3-CaS and (Mg, Mn, Ca)S in REMs-free steel were modified into composite ones of MgO·Al2O3-LaAlO3, La2O2S-MgO and (La, Ca)S in the steel with 0.0006% lanthanum, and to (La, Ce)2O2S-CaS-MgO, (Ce, La)S in the steel with 0.0007% lanthanum and 0.0015% cerium. The number density of fine MnS was remarkably decreased by the addition of REMs, leading to an increase in the average grain size. The steel containing 0.0006 wt% lanthanum possessed the best combination of core loss and magnetic induction due to the decrease of micro-sized inclusions and fine MnS, the increase of grain size, and the optimization of recrystallization textures. For the steel with excess REMs addition, the large number density of rare earth sulfides with the size of approximately 1 μm tended to deteriorate the grain size and textures.