Search Results (749)

Rare earth elements (REEs) are not scarce in nature; however, they rarely occur in economically viable concentrations. Over recent decades, demand for REE has increased substantially due to advances in high-technology industries and the expansion of clean energy technologies. At present, global REE production is highly concentrated, leading to instability in the international market and reinforcing the need to identify new resources. This study presents a mineralogical characterization of REE+Y occurrences in the Serra da Mesa Granitic Massif (SMGM), the type granite of the Tocantins Subprovince, Goiás Tin Province, Brazil. The objective is to evaluate its potential for REE+Y enrichment in ion-adsorption–type (IA-type) weathering profiles. Petrography, electron probe microanalysis (EPMA), and scanning electron microscopy (SEM) were applied to samples of the parental granite and associated alluvial sediments. The main REE-bearing minerals identified are allanite, bastnäsite-(Y), fluocarbonates, xenotime-(Y), zircon, and fergusonite-(Y), showing wide compositional variability. Bastnäsite-(Y) and xenotime display the highest REE+Y contents, reaching up to 74.2 wt.% and 65.1 wt.%, respectively. Bastnäsite and other fluocarbonates occur as alteration products of allanite, indicating REE+Y mobilization associated with F- and CO₂-rich fluids under low-temperature hydrothermal conditions. Alteration textures and low EPMA analytical totals suggest hydration, metamictization, and fluid-mediated neoformation processes. The abundance of REE+Y-bearing minerals, their susceptibility to weathering, and the presence of secondary fluocarbonates indicate that the SMGM represents a promising target for IA-type REE+Y mineralization within the Goiás Tin Province. Full article

The efficient recovery of rare earth elements (REEs) from low-concentration mine tailwater is crucial for resource sustainability. In this study, a novel composite adsorbent, sesame stalk biochar-supported zirconium phosphate (sBC/ZrP), was synthesized for the selective adsorption and recovery of La³⁺ as a representative REE. The material was characterized using SEM-EDS, BET, XRD, FTIR, and XPS. Batch adsorption experiments were conducted to evaluate the effects of pH, coexisting ions, and the adsorption kinetics and thermodynamics. The results showed that sBC/ZrP exhibited a high adsorption capacity (up to 185.83 mg/g at 35 °C for 4 h) and strong selectivity for La³⁺, particularly in the presence of common competing cations, although Al³⁺ demonstrated significant interference. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model, indicating monolayer chemisorption, and was determined to be spontaneous and endothermic. The material maintained over 90% adsorption efficiency after five consecutive adsorption–desorption cycles. The mechanism primarily involved complexation of La³⁺ with the P-OH and Zr-O groups on the composite. This work demonstrates that sBC/ZrP is a highly efficient, stable, and reusable adsorbent with significant potential for the recovery of REEs from mining tailwater. Full article

Precise control over defect structures is essential for tuning the functional properties of lithium niobate (LiNbO₃) crystals. Although the threshold effect of Hf⁴⁺ doping is well recognized, its underlying atomic-scale mechanism, especially in systems co-doped with luminescent rare earth ions, remains unclear. In this study, we combine experimental and theoretical approaches to elucidate the Hf⁴⁺ concentration-driven threshold behavior in Dy: LiNbO₃ crystals. A series of crystals with Hf⁴⁺ concentrations of 2, 4, 6, and 8 mol% were grown using the Czochralski method. Characterization through XRD and IR spectroscopy identified a threshold near 4 mol%, evidenced by an inflection in lattice constants and a pronounced blue shift of the OH⁻ absorption peak. UV–Vis–NIR absorption spectra revealed a systematic enhancement of Dy³⁺f–f transition intensities, linking the global defect structure to the local crystal field of the optical activator. First-principles calculations showed that Hf⁴⁺ ions preferentially occupy Li sites, repairing antisite Nb defects ($\mathrm{N}{\mathrm{b}}_{\mathrm{Li}}^{4+}$) below the threshold, and incorporate into Nb sites beyond it, inducing structural reorganization. Electron Localization Function analysis visualized strengthened Hf-O covalent bonding in the post-threshold regime. This work establishes a complete atomic-scale picture connecting dopant site preference, chemical bonding, and macroscopic properties, providing a foundational framework for the rational design of advanced LiNbO₃-based materials. Full article

Intrinsic optical bi-stability in dense two-level systems is developed for the bad cavity limit where electromagnetic modes are adiabatically eliminated. Each atom interacts via dipole–dipole forces with its nearby spatial distribution of atoms. The theory is developed into two parts, corresponding to the short sample, with dimensions shorter than the wavelength, and the long sample. In both cases, the local field corrections modify the Maxwell–Bloch equations, so that cubic or quartic equations are obtained for the inversion of population as a function of the external light intensity, thus leading to intrinsic bi-stability. The effects of noise sources on intrinsic bi-stability were treated, and I found that while the observability of bi-stability was not obtained experimentally for a simple two-level system, there were many observations of bi-stability obtained through the ‘up-conversion’ of rare earth excited crystals. I show the differences between these two systems. Full article

In a seminal paper V.M. Goldschmidt pointed out that, in terms of volume of the constituent ions, Earth’s crust and mantle are basically a packing of negatively charged oxygen ions bound together by the volumetrically barely significant cations. Here, this statement is revisited using modern assessments of mantle composition and pressure-dependent ionic radii. It is found that the transition to the lower mantle marks a reduction in the O²⁻ crystal ionic volume percentage from 86 to less than 80%, significant enough to suggest an overall reduced compatibility of less abundant elements within the first few hundred km of depth below that transition from lower-mantle to upper-mantle rock. An equivalent drop across both, the 410- and 670 km mantle discontinuities occurs for large polyhedral sites, which are the potential hosts for incompatible elements. Accordingly, most large ionic lithophiles and rare earth elements in the lower mantle are highly enriched in one minor phase, davemaoite. It is proposed that those minor and trace elements that are less compatible with this mineral, such as some of the high-field strength elements, are concentrated in yet unknown accessory minerals that potentially affect geochemical signatures of deep mantle-derived igneous rocks. Full article

The most widely used chelating agent, ethylenediaminetetraacetic acid (EDTA), can cause mild to serious side effects when used for clinical applications. Introducing a polyethylene glycol (PEG) moiety into the molecular structure of EDTA has been shown to lower its toxicity; however, it is unclear whether this could affect EDTA chelation efficiency due to the steric hindrance and the loss of a coordination site caused by the PEGylation reaction. This research aimed to determine if PEGylation could reduce EDTA toxicity without affecting its chelation efficiency. To this end, effective formation constants were determined for EDTA and PEG-EDTA rare earth metal ion complexes using spectrophotometric and titrimetric methods. The stability of PEG-EDTA complexes with the target metal ions was assessed under different conditions using Fourier-transform infrared spectroscopy. The cytotoxicity and metal detoxification capacity of EDTA, PEG-EDTA, and their zinc(II) complexes were determined in two selected human cell types exposed to toxic heavy metal ions. This study suggests that PEG-EDTA has lower toxicity than EDTA, especially when complexed with a nontoxic metal ion, such as zinc(II), while only slightly losing chelation efficiency, potentially making PEG-EDTA a more favourable metal detoxification reagent for clinical applications. Full article

The voluminous Mesozoic volcanic rocks developed in the Great Xing’an Range, northeastern China, have received extensive attention in recent decades. However, the timing and petrogenesis, as well as the related geodynamic processes of the Late Mesozoic volcanism, are still controversial. In this paper, we present the whole-rock geochemistry and zircon U–Pb ages for the Late Mesozoic volcanic rocks from the western part of the central Great Xing’an Range, which provide considerable insights into the geodynamic setting of the region. The zircon U-Pb dating results indicate that two main episodes of volcanism occurred in the central Great Xing’an Range, including in the Late Jurassic (ca. 147 Ma) and Early Cretaceous (ca. 142–125 Ma). These Late Mesozoic volcanic rocks display similar geochemical compositions, which are mainly intermediate–felsic, alkaline, peraluminous to metaluminous, enriched in large ion lithophile elements and light rare earth elements, and depleted in high-field-strength elements, indicating arc affinities in the subduction zone. The trace element compositions suggest that the magmatism was related to a post-collisional extensional environment. Combined with the spatial distribution and temporal migration of the Mesozoic magmatic events in the whole northeastern China region, we propose that these Late Jurassic–Early Cretaceous volcanic rocks formed in a continental arc setting, which was mainly related to the rollback of the subducted Paleo-Pacific oceanic plate. Full article

The optimization of BiVO₄-based structures significantly contributes to the development of a global system towards clean, renewable, and sustainable energies. Enhanced photocatalytic performance has been reported for numerous doped BiVO₄ materials. Bi³⁺-based compounds can be easily doped with rare earth (RE³⁺) ions due to their equal valence and similar ionic radius. This means that RE³⁺ ions could be regarded as active co-catalysts and dopants to enhance the photocatalytic activity of BiVO₄. In this study, a simple microwave-assisted approach was used for preparing nanostructured Bi_1−xEu_xVO₄ (x = 0, 0.03, 0.06, 0.09, and 0.12) samples. Microwave heating at 170 °C yields a bright yellow powder after 10 min of radiation. The materials are characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible–near-infrared diffuse reflectance spectroscopy (UV-Vis-NIR DRS), photoluminescence spectroscopy (PL), and micro-Raman techniques. The effects of the different Eu³⁺ ion concentrations incorporated into the BiVO₄ matrix on the formation of the monoclinic scheelite (ms-) or tetragonal zircon-type (tz-) BiVO₄ structure, on the photoluminescent intensity, on the decay dynamics of europium emission, and on photocatalytic efficiency in the degradation of Rhodamine B (RhB) were studied in detail. Additionally, microwave chemistry proved to be beneficial in the synthesis of the tz-BiVO₄ nanostructure and Eu³⁺ ion doping, leading to an enhanced luminescent and photocatalytic performance. Full article

Rare-earth oxide (REO) nanoparticles (NPs)—such as cerium (CeO₂), samarium (Sm₂O₃), neodymium (Nd₂O₃), terbium (Tb₄O₇), and praseodymium (Pr₂O₃)—have demonstrated strong antimicrobial activity against multidrug-resistant bacteria. Their effectiveness is attributed to unique physicochemical properties, including oxygen vacancies and redox cycling, which facilitate the generation of reactive oxygen species (ROS) that damage microbial membranes and biomolecules. Additionally, electrostatic interactions with microbial surfaces and sustained ion release contribute to membrane disruption and long-term antimicrobial effects. REOs also inhibit bacterial enzymes, DNA, and protein synthesis, providing broad-spectrum activity against Gram-positive, Gram-negative, and fungal pathogens. However, dose-dependent cytotoxicity to mammalian cells—primarily due to excessive ROS generation—and nanoparticle aggregation in biological media remain challenges. Surface functionalization with polymers, peptides, or metal dopants (e.g., Ag, Zn, and Cu) can mitigate cytotoxicity and enhance selectivity. Scalable and sustainable synthesis remains a challenge due to high synthesis costs and scalability issues in industrial production. Green and biogenic routes using plant or microbial extracts can produce REOs at lower cost and with improved safety. Advanced continuous flow and microwave-assisted synthesis offer improved particle uniformity and production yields. Biomedical applications include antimicrobial coatings, wound dressings, and hybrid nanozyme systems for oxidative disinfection. However, comprehensive and intensive toxicological evaluations, along with regulatory frameworks, are required before clinical deployment. Full article

The tectonic evolution of the Paleo-Asian Ocean during the Early to Middle Permian remains a key issue in understanding the geodynamic history of the Central Asian Orogenic Belt. To address this, we conducted petrological, whole-rock geochemical, zircon U–Pb geochronological, and Hf isotopic analyses of Early Permian biotite granodiorite and Middle Permian porphyritic granite from the south-central Great Xing’an Range. Zircon U–Pb dating yields ages of 273.2 ± 1.4 Ma and 264.4 ± 1.5 Ma, indicating that these intrusions emplaced during Early and Middle Permian. Geochemical analyses show that the rocks are characterized by high SiO₂ and Al₂O₃ contents, and low MgO and CaO contents and belong to the metaluminous to weakly peraluminous series, typical of I-type granites. The rocks are enriched in light rare earth elements and large-ion lithophile elements (e.g., Rb, Ba, K), but depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, P, Ti), with weakly negative Eu anomalies. The Early Permian pluton exhibits low-Sr and high-Yb characteristics and thus fall in the plagioclase stability field. In contrast, Middle Permian pluton was derived from magmas generated by partial melting under high-pressure conditions and that, underwent crystal fractionation during ascent to the mid-upper crust, ultimately forming low-Sr and low-Yb type granites. All zircon ε_Hf(t) values are positive (+4.84 to +14.87), with the corresponding two-stage Hf model ages ranging from 345 Ma to 980 Ma, indicating that the magmas were predominantly derived from juvenile crustal materials accreted during the Neoproterozoic to Phanerozoic. Considering these results, we propose that the Paleo-Asian Oceanic plate continued to subduct beneath the Songliao–Xilinhot block to the north during the Early to Middle Permian, with intense subduction and crustal thickening occurring in the Middle Permian. This suggests that the south-central segment of the Great Xing’an Range was situated in an active continental marginal setting during the Early-Middle Permian. Full article

We establish a general, device-oriented procedure to extract absolute pump-band metrics from room-temperature UV–Vis (ultraviolet–visible) absorbance—including the absorption coefficient α(λ), per-active-ion cross-section ${\sigma }_{\mathrm{e}\mathrm{f}\mathrm{f}}\left(\lambda \right)$, the effective per-active-ion absorption cross section ${\sigma }_{\mathrm{e}\mathrm{f}\mathrm{f}}\left(\lambda \right)$ and derivative-based line-shape descriptors. As a representative case study, the procedure is applied to nanocrystalline Er³⁺/Ho³⁺:Y₃Ga₅O₁₂ over the 350–700 nm spectral range. After baseline correction and line-shape inspection assisted by the numerical second derivative of the absorbance, we extract conservative peak positions and the full width at half maximum across the visible 4f–4f manifolds. At the technologically relevant pump wavelengths near 406 nm (Er-addressing) and 473 nm (Ho-addressing) bands, resulting absorption coefficients are α = 0.313 ± 0.047 cm⁻¹ and α = 0.472 ± 0.071 cm⁻¹, respectively. The corresponding per-active-ion ${\sigma }_{\mathrm{e}\mathrm{f}\mathrm{f}}$ of (3.62 ± 0.54) × 10⁻²² cm² and (5.46 ± 0.82) × 10⁻²² cm², referenced to the measured optical path length L = 0.22 ± 0.03 mm (approximately 15% propagated relative uncertainty; explicit 1/L rescaling). Cross sections are reported per total active-ion density (Er³⁺ + Ho³⁺). The spectra exhibit Stark-type substructure only partially resolved at room temperature; the second derivative highlights hidden components, and we report quantitative descriptors (component count, mean spacing, curvature-weighted prominence, and pump detuning) that link line-shape structure to absolute pump response. These device-grade metrics enable rate-equation modelling (pump thresholds, detuning tolerance), optical design choices (path length, single/multi-pass or cavity coupling), and host-to-host benchmarking at 295 K. The procedure is general and applies to any rare-earth-doped material given an absorbance spectrum and path length. Full article

Zero-dimensional (0D) rare-earth-based metal halides show great potential in photonic and optoelectronic applications owing to their high stability, strong exciton confinement, and tunable energy levels. However, the weak absorption and narrow 4f-4f transitions of rare-earth ions limit their performance. To address this, a series of Sb³⁺-doped Cs₃LnCl₆ (Ln: Yb, La, Eu, Ho, Ce, Er, Tb, Sm, Y) nanocrystals were synthesized via a hot-injection method to study the role of Sb³⁺ doping. Sb³⁺ incorporation induces strong broadband self-trapped exciton (STE) emission from Jahn–Teller-distorted [SbCl₆]³⁻ units and enables efficient energy transfer from STEs to rare-earth ions. As a result, the photoluminescence intensity and spectral tunability are improved, accompanied by bandgap narrowing and enhanced light absorption. Different lanthanide hosts exhibit distinct luminescence behaviors: La-based materials show dominant STE emission, while Tb-, Er-, Yb-, Ho-, and Sm-based systems display STE-mediated energy transfer and enhanced f-f emission. In Eu- and Ce-based hosts, unique mechanisms involving Eu²⁺/Eu³⁺ conversion and Ce³⁺ → STE energy transfer are observed. Moreover, composition-dependent emissions in Sb³⁺-doped Cs₃Tb/EuCl₆ enable a dual-mode color and spectral encoding strategy for optical anti-counterfeiting. This study highlights the versatile role of Sb³⁺ in tuning electronic structures and energy transfer, offering new insights for designing high-performance rare-earth halide materials for advanced optoelectronic applications. Full article

Long persistent phosphors are widely used in many fields, such as LED, bioimaging, urgent lighting, temperature sensors, etc. Although green and blue long persistent phosphors are well developed, efficient orange-yellow long persistent phosphors are still relatively rare. In this work, a novel orange-yellow long-persistent phosphors Ca₂LuScGa₂Ge₂O₁₂:xPr³⁺ (CLSGGO:xPr³⁺, x = 0.003, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05) are prepared and systematically investigated through its crystal structural information, photoluminescence, and persistent luminescence properties. Under ultraviolet light excitation, these phosphors exhibit orange-yellow emission stemming from the ³P₀ and ¹D₂ multiple electron transitions in the 4f level of Pr³⁺ ion. In addition, the material exhibits bright persistent luminescence. The complex garnet matrix structure of Ca₂LuScGa₂Ge₂O₁₂ provides excellent conditions for the formation of traps. Through the testing of thermoluminescence curve and function fitting, the density and depth of traps are studied; also, the storage and release process of carriers in the material are calculated in detail. A reasonable persistent luminescence mechanism is proposed for CLSGGO:0.01Pr³⁺. This work enriches the research content of photoluminescence and long persistent luminescence of Pr³⁺-doped garnet-based phosphors and paves the way for the future research of long persistent luminescent materials doped with rare earth ions. Full article

Ion adsorption rare-earth (IARE) ores, a strategic metal resource, are extracted by leaching with ammonium sulfate [(NH4)₂SO₄] solution, our samples have ∑REO grades of 0.032–0.079% wt%. IARE sandstone, mudstone, clay, and strongly weathered rock were selected as test materials. Surface-related physicochemical parameters were determined, and bound water was determined by volumetric flask pycnometry. For each IARE lithology, we also obtained particle size distributions and evaluated bound water variation in (NH₄)₂SO₄ solutions at 0, 1, 2, and 3 wt%. Based on the Gouy–Chapman theory, the relationship between the surface bound water and solution concentration, as well as the surface charge of IARE samples, and other influencing factors was explored. The experimental results show the following: ① The surface charge per unit area of four types of IARE samples, namely mudstone, sandstone, clay, and strongly weathered rock, are 0.7072 × 10⁻² mmol/m², 1.9620 × 10⁻² mmol/m², 1.5418 × 10⁻² mmol/m², and 2.1003 × 10⁻² mmol/m², respectively, with strongly weathered rock having the highest and mudstone having the lowest. ② As the concentration of aqueous (NH₄)₂SO₄ increases (0, 1, 2, 3 wt%), the total volume reduction in free water ∆V in the system increases, and the mass of adsorbed bound water per unit mass of IARE sample also increases. ③ As the concentration of the solution increases, the thickness of the diffusion double layer on the surface of the IARE sample is compressed, the total amount of adsorbed anions and cations on the surface increases, and the density of the surface water film also increases, leading to a corresponding increase in the quality of adsorbed bound water. ④ Under the same solution concentration, the variation trend of adsorbed bound water mass per unit area of IARE samples is strongly weathered rock > sandstone > clay > mudstone, which is consistent with the trend of surface charge per unit area of IARE samples. A higher lixiviant concentration increases bound water, shrinks the effective pore throats of the ore body, reduces hydraulic conductivity, and consequently diminishes leaching efficiency. Full article

The Zhilingtou Au-Mo-Pb-Zn polymetallic deposit is located in the southwestern Zhejiang Province, NE China, and is tectonically situated in the Shaoxing-Longquan uplift belt. Although previous studies have indicated that Au mineralization in this area occurred between 135 Ma and 145 Ma, evidence for coeval intrusive rocks has been lacking. Furthermore, it remains controversial whether the Au mineralization and (~113 Ma) Mo-Pb-Zn mineralization belong to the same magmatic-hydrothermal system. This study conducted comprehensive high-precision geochronological, petrochemical, and Sr-Nd isotopic analyses on the newly discovered granite porphyry intrusion in the mining area. The aim is to constrain the emplacement age of the intrusion, reveal the petrogenesis and source of ore-forming materials, and further discuss the mineralization mechanism. LA-ICP-MS zircon U-Pb dating results indicate that the granite porphyry was formed at 137.8 ± 0.95 Ma, which is broadly consistent with previously reported ages of Au mineralization. It is inferred that this intrusion may be related to a Au mineralization event at around 138 Ma. Geochemical characteristics show that the rock is peraluminous I-type granite, enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti, indicating an “island arc-type” geochemical signatures. Sr-Nd isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr = 0.712364–0.712711; ε_Nd(t) = −13.9 to −13.4; two-stage Nd model ages T_DM2 = 1877–1908 Ma) suggest that the magma was derived from ancient crustal materials with the addition of mantle-derived components. Integrating existing geochronological, isotopic, and fluid inclusion evidence, it is proposed that the Zhilingtou deposit may have experienced two mineralization events: an early event (~138 Ma) involving Au-Ag mineralization related to the granite porphyry and a later event (~113 Ma) comprising Mo-Pb-Zn mineralization associated with a porphyry–epithermal system. Together, these events form a composite mineralization system. This study has important implications for refining regional metallogenic theories and guiding future ore exploration. Full article