Physics

The development of efficient phosphors with favourable optoelectronic properties is essential for improving white lighting diodes (wLEDs) and other optoelectronic applications. In this study, self-activated red-emitting La 2 ZnTiO 6 (LZTO) nanophosphors were synthesised via the sol-gel method, and the influence of annealing time on their thermal, structural, morphological, and optical properties were systematically investigated. Thermogravimetric analysis confirmed thermal stability at 1000 ℃. X-ray powder diffraction results confirmed the formation of single-phase monoclinic LZTO with the P 21/ n space group and enhanced crystallinity after annealing. X-ray photoelectron spectroscopy confirmed the presence of La, Zn, Ti, and O, indicating high chemical purity, while Field-emission scanning electron microscopy revealed progressive morphological evolution with annealing. UV–visible diffuse reflectance spectra exhibited two absorption band edges located at 300–333 nm and 376–390 nm, with the indirect optical bandgap ranging from 3.14 to 3.20 eV. Under 3.17 eV excitation, LZTO exhibited reddish-orange emission with prominent red bands at 1.82, 1.75, and 1.68 eV, which were primarily associated with oxygen-vacancy-related defects and surface states. The emission intensity increased with annealing time and reached an optimum after 6 h. Temperature-dependent PL measurement revealed gradual thermal quenching from 303 to 423 K. At 423 K, only 5.65% of the initial emission intensity was retained, indicating limited thermal stability. Nevertheless, the Commission Internationale de l’Éclairage chromaticity coordinates showed negligible temperature variation, demonstrating good colour stability. These findings highlight the potential of annealed LZTO nanophosphors as self-activated red-emitting materials for high-quality solid-state lighting and related optoelectronic technologies and systems.

Defining the initial porosity limits within which hot isostatic pressing (HIP) can effectively densify laser powder bed fusion (PBF-LB) components remains a critical gap for industrial qualification of additively manufactured nickel-based superalloys. This study systematically investigates the influence of volumetric energy density (VED) on initial defect population in Inconel 718 (IN718) and its role in densification response during HIP. Specimens with varying initial porosity (0.01% to 17.76%) were fabricated by intentionally varying laser power, scan speed, and hatch spacing. All samples were subjected to identical HIP conditions (1160 °C, 100 MPa, 4 h) incorporating a combined in-situ solution treatment, followed by double ageing in a vacuum furnace. Porosity evolution, pore morphology, microstructural transformations, and nano-mechanical response were characterized before and after HIP. Three distinct densification regimes were identified based on initial porosity. Below 0.1%, the absolute densification benefit is negligible due to argon-filled gas pores resistant to closure. Between 0.1% and 10%, closure efficiencies of 87–98% are achieved, representing the optimal HIP densification window. Between 10% and 17%, the response degrades progressively, and above ~17% densification efficiency becomes negative owing to open-pore network formation and argon gas expansion during subsequent vacuum treatments. Furthermore, HIP at 1160 °C fully dissolved Nb-rich laves phases, eliminated melt pool boundaries, and promoted recrystallization from columnar to equiaxed grain structure. Double ageing produced a uniform distribution of fine γ′/γ″ strengthening precipitates. These findings establish quantitative defect acceptance criteria for pre-HIP qualification of PBF-LB nickel superalloy components, supporting cost-effective post-processing for aerospace and energy applications.

Abstract Various framework materials offer potential platforms for developing next-generation electro-responsive functional and smart materials because they are electro-active or polarizable by either ions in channels or electrons in frameworks. However, the present framework materials still face challenges in achieving high electro-response while maintaining low charge leakage or electrode polarization. In this study, we developed a kind of bipolar carbonaceous framework (CF) materials codoped with pyridinic nitrogen and graphitic nitrogen, which can simultaneously provide local electrons and holes, via an ionothermal polymerization of task-specific ionic liquid at target temperature. The structure of CF was characterized by thermogravimetric analysis, Fourier transform infrared spectra, solid-state nuclear magnetic resonance spectra, wide-angle X-ray scattering spectra, and X-ray photoelectron spectra, and the bipolar charge characteristic was analyzed by Mott–Schottky curves and photocurrent measurements. Dielectric spectra of the CF particles in suspensions were measured and showed enhanced interfacial polarization but very weak electrode polarization and leakage conduction due to the coupled movement of electrons and holes. Consequently, the bipolar CF suspensions show significantly higher electro-responsive electrorheological effect (τs = 12 kPa@3 kV/mm) and lower current density (j = 46 μA/cm2@3 kV/mm) compared to single electron-dominated, single ion-dominated, and even mixed ionic-electronic systems. So, this bipolar CF provides a preferred platform for the design of high-performance carbonaceous-based electro-responsive functional and smart materials.

Abstract Targeted halide substitution provides an effective route to access structural motifs in thio-LISICON systems. Here, partial substitution of S2– by Cl– in Li4GeS4 stabilizes a hexagonal polymorph near the composition Li3.25GeS3.25Cl0.75. Ab initio structure determination by joint refinement of time-of-flight neutron powder diffraction and X-ray diffraction data supports a P63mc average structure built on a hexagonal close-packed anion framework. The resulting framework exhibits a distinct Li-site topology with symmetry-inequivalent Li environments, including a shared tetrahedral framework site and additional tetrahedral and octahedral interstitial sites. Systematic investigation of the Li4–xGeS4–xClx series shows that the hexagonal phase is preferentially stabilized near the nominal x = 0.75 composition, for which no secondary crystalline phase was detected by PXRD. Structural analysis indicates that halide substitution produces a rearranged and partially disordered Li substructure. Bond-valence energy landscape calculations show that the computed Li-energy topology is highly sensitive to the representation of Li/Ge occupational disorder, with a Ge-free sensitivity model recovering the crystallographic Li1-related minimum and markedly altering the calculated percolation topology. Li3.25GeS3.25Cl0.75 exhibits a room-temperature ionic conductivity of 3.91 × 10–6 S cm–1. These results demonstrate that halide substitution can stabilize hexagonal polymorphs and reorganize the Li substructure in sulfide solid electrolytes, providing a platform for examining how structural disorder and Li-site topology influence ion transport.