Jianguo Wen

Self‐trapped excitons (STEs) play an important role in the luminescence of halide materials, yet their formation and manipulation in complex fluorides remain largely underexplored. Here, Mn ⁴⁺ ‐doped Li ₂ HfF ₆ phosphors were synthesized by room‐temperature coprecipitation to investigate impurity‐modulated STEs and their role in Mn ⁴⁺ sensitization. High‐resolution neutron powder diffraction reveals impurity‐associated phase separation into two closely related Li ₂ HfF ₆ lattices. Photoluminescence and cathodoluminescence measurements resolve two broad host‐emission components: STE1, assigned to intrinsic Li ₂ HfF ₆ , and redshifted STE2, associated with a K‐containing lattice. Under high‐energy cathodoluminescence excitation, enhanced Mn ⁴⁺ red emission correlates with STE2 emission but not with STE1 emission, supporting a selective STE2 → Mn ⁴⁺ energy‐transfer pathway. Density functional theory ΔSCF (self‐consistent field) calculations yield distinct relaxed STE1 and STE2 configurations, confirming the K‐induced redshift of the STE emission. These results identify K‐associated STE2 as a key sensitizing state for Mn ⁴⁺ luminescence, establishing impurity modulation as an effective strategy for tuning excitonic emission and host‐to‐activator energy transfer in complex fluoride phosphors.

The rapid growth of lithium‐ion batteries is intensifying pressure on critical‐material supply chains while generating increasing volumes of complex battery waste. However, existing recycling technologies struggle to process mixed feedstocks efficiently and often recover products with limited added value. Here, we advance beyond cathode‐focused hydrometallurgical recycling by integrating composition‐adjustable cathode resynthesis with the purification and surface modification of co‐recovered graphite, followed by full‐pouch‐cell validation and unified process‐level assessment. Mixed low‐nickel cathodes are upgraded to high‐performance LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (NMC622) with improved lithium‐ion transport and cycling stability. Meanwhile, a closed‐loop graphite upcycling process produces battery‐grade anodes with enhanced interfacial kinetics and durability. Full pouch cells assembled entirely from the upcycled materials exhibit fewer side reactions and approximately twice the cycle life of cells using commercial counterparts, retaining 70% of their capacity after 2590 cycles. Techno‐economic and life‐cycle analyses further indicate >95% recycled‐material utilization, 22.9% higher profitability, and reductions of 27.0% in greenhouse‐gas emissions and 29.4% in energy consumption relative to the reference recycling route. These findings establish mixed battery waste as a viable feedstock for producing high‐value battery materials and demonstrate a pathway from conventional resource recovery toward value‐added remanufacturing for circular, resilient, and low‐carbon battery supply chains.

Defects trap photocarriers and hinder solar water splitting. The nanoscale photocarrier transport, trapping, and recombination mechanisms are usually inferred from ensemble-averaged measurements and remain elusive. Because an individual high-performing nanoparticle photocatalyst may outperform the ensemble average, design rules that would otherwise enhance catalytic efficiency remain unclear. Here, we introduce photomodulated electron energy-loss spectroscopy (EELS) in an optically coupled scanning transmission electron microscope (STEM) to map photocarrier localization. Using rhodium-doped strontium titanate (SrTiO ₃ :Rh) solar water-splitting nanoparticles, we directly image the carrier densities concentrated at oxygen-vacancy surface trap states. This is achieved by separating photothermal heating from photocarrier populations through experimental and computational analyses of low-loss spectra. Photomodulated STEM-EELS enables angstrom-scale imaging of defect-induced photocarrier traps and their impact on photocatalytic efficiency.

High‐nickel layered oxides are the leading commercial cathode candidates for lithium‐ion batteries, yet their widespread deployment remains constrained by limited cycling stability. Niobium (Nb) coating/doping has emerged as an effective mitigation strategy, but current approaches typically rely on wet‐chemical or gas‐phase routes that are difficult to scale. Herein, we report a dry process that achieves homogeneous Nb ⁵⁺ doping into Li ₁ Ni _0.83 Mn _0.05 Co _0.12 O ₂ by treating the precursor with ultrafine Nb ₂ O ₅ nanoparticles synthesized via flame spray pyrolysis. With only 0.5 mol.% Nb ⁵⁺ , the doped material exhibits improved lattice ordering and refined particle architecture, delivering high capacity up to 211 mAh g ⁻¹ , exceptional capacity retention 97% after 100 cycles in half cell, and markedly improved rate capability (170 mAh g ⁻¹ at 5C) and long‐term cyclability (83% over 500 cycles at 1C) in full cells. Multiscale structural and chemical analyses reveal the crucial role of ultrafine Nb ⁵⁺ addition at the precursor stage in modifying the grain morphology, which ends in homogeneous doping providing mitigation of intergranular cracking and suppression of surface rock‐salt reconstruction, thereby preserving coherent grain boundaries under extended cycling. This work highlights the mechanistic effectiveness of homogeneous Nb ⁵⁺ doping via dry process in microstructural control and stabilization of high‐nickel cathodes.

In two-dimensional transition metal dichalcogenides such as tungsten diselenide (WSe₂), single photon emission has been broadly attributed to exciton localization from atomic point defects, yet the precise microscopic origins are unclear. This work introduces an empirically grounded computational framework that explains the origins of facile single photon emission in WSe₂. High-resolution microscopy identifies native defect geometries in monolayer WSe₂ lattices from which the model is built. The qualitative effects of chalcogen type, defect geometry, and mechanical strain on the electronic structure are individually assessed using density functional theory, and a specific divacancy configuration emerges as the candidate for localized single-electron transitions that match observed spectral energies. Spectroscopy and photon correlation measurements further validate this model, establishing a self-consistent link between defect geometry, electronic structure, and quantum emission.

Modern high‐electron‐mobility transistors (HEMTs) and light‐emitting diodes (LEDs) are engineered around epitaxial indium gallium nitride (In _x Ga _1 − x N) heterostructures. We apply the highest‐resolution structural, elemental, and optical characterization to a series of systematically fabricated GaN‐on‐silicon (Si) epitaxial heterostructures and demonstrate hitherto unresolved nanoscale optical inhomogeneities in individual In _x Ga _1 − x N quantum wells. Direct correlation of atom probe tomography and scanning transmission electron microscopy with cathodoluminescence collectively confirms that these optical inhomogeneities result from compositional segregation that only appears in high indium‐content In _x Ga _1−x N specimens, but not in low indium‐content quantum wells, thereby elucidating the origin of injection‐current‐induced blueshifts in long wavelength LEDs. Density functional theory (DFT) calculations of the various alloy mixing energies indicate that the relaxation of the epitaxial in‐plane strain stabilizes specific In _x Ga _1−x N compositions. Our findings suggest that proper use of strain management and careful selection of alloy compositions are necessary to control local phase separation. This work presents a path to high‐mobility strain engineering in HEMTs and homogeneous, long‐wavelength light emission in LEDs.

We report a drastic difference in stacking behavior of oleic acid-stabilized 4-monolayer (4 ML) CdSe nanoplatelets (NPLs) in toluene and methylcyclohexane (MCH), two nonpolar solvents that differ in the conformational flexibility of their molecules. Using liquid cell transmission electron microscopy (TEM) and small angle scattering (SAXS) techniques, we show that NPLs form microns-long ribbons consisting of 4 ML CdSe NPLs in toluene, the solvent widely used to form stable colloidal solutions of a broad range of quasi-spherical nanoparticles. In contrast, 4 ML CdSe NPLs are well dispersed in MCH. The difference in stacking behavior of NPLs in toluene and MCH suggests that the conformational flexibility of the solvent molecules, such as the ability to adopt multiple chair conformations, modulates nanoplatelet interactions. Molecular dynamics (MD) simulations reveal that solvent molecules subtly alter the structure of the organic ligand shell. These solvent-dependent changes propagate to the inorganic core, modulating the degree of CdSe nanoplatelet (NPL) twisting and, consequently, the properties of the nanoparticles. We show that toluene better solvates oleate ligands while MCH induces a bimodal oleate span distribution, which can lead to increased solubility of CdSe NPLs. In addition, the solvent can also influence the inorganic core, which, in turn, can modify the nanoparticle properties. We demonstrate that destabilization of toluene solution containing ribbons of 4 ML CdSe NPLs without CdS shells results in the formation of NPL assemblies with amplified spontaneous emission (ASE) with a low threshold of 14 µJ cm⁻² that is comparable with that of CdSe/CdS core/shell NPLs. Our results emphasize that the solvent plays a major role in mediating interactions between NPLs and hence their processability for fabrication of functional structures.

Two-dimensional (2D) superconductors with spin-textured Fermi surfaces can be a platform for realizing unconventional pairing states and are of substantial interest in the context of quantum information science and superconducting spintronics/orbitronics. We observed an unusual in-plane uniaxial anisotropy in the superconducting 2D electron gas (2DEG) formed at EuO _x /KTaO ₃ (110) interfaces. This anisotropy is not evident in AlO _x /KTaO ₃ (110) where the overlayer is nonmagnetic. Our results are consistent with a highly anisotropic “half-Rashba” spin-textured Fermi surface in 2DEGs formed at the KTaO ₃ (110) interface that is hidden from external magnetic fields due to a near cancellation between orbital and spin moments but revealed by exchange interactions of the electrons in the 2DEG with Eu moments near the EuO _x /KTaO ₃ (110) interface. The interactions between the uniaxial spin texture and the magnetic overlayer offer previously unexplored ways to explore the interplay between magnetism and 2D superconductivity.

Nanoarchitectonics offers a systematic approach to creating an artificial framework by integrating different multiscale components such as semiconductor lattices and biological substances. However, most nanoarchitectonic abiotic-biotic hybrid systems have intrinsic limitations in imparting nonequilibrium biological features into semiconductor lattices at the nanoscale. Here, we report a new nanoarchitectonic system integrating bismuth oxychloride (BiOCl) nanosheets with purple membrane (PM) patches. PM is an archaeal subcellular fraction capable of unidirectionally transferring photogenerated charge carriers to its surroundings at the nanoscale independent of archaeal metabolism and retaining this dynamic functionality after isolation from living archaea. Microscopy, spectroscopy, electrochemical, and synchrotron X-ray scattering analyses verify that the nanoarchitectonic hybridization between BiOCl and PM generates a vertical heterostructure, thereby enhancing photogenerated charge-carrier dynamics and enabling the associated photocatalytic capacity. The resulting PM-BiOCl hybrid nanosheets efficiently convert dioxygen into hydrogen peroxide through a two-electron and two-proton transfer process under ambient conditions while simultaneously converting ethylene glycol into value-added chemicals. This study presents a nanoarchitectonic approach that leverages the photogenerated charge-carrier dynamics of the archaeal subcellular fractions to modulate the optoelectronic and catalytic capacity limitations of semiconductors.