Search Results (180)

Near-ultraviolet-excitable red phosphors with high thermal stability are desirable for phosphor-converted LED applications, including potential plant-lighting applications. Herein, Sm³⁺- and Eu³⁺-activated Na₃YB₈O₁₅ phosphors were synthesized by a high-temperature solid-state reaction. Among the investigated compositions, the optimal activator contents were identified as x = 0.02 for Na₃YB₈O₁₅:xSm³⁺ and y = 0.70 for Na₃YB₈O₁₅:yEu³⁺, with concentration quenching in both series mainly governed by dipole–dipole interactions. In the Sm³⁺/Eu³⁺ co-doped phosphors, the emission color shifted from orange-red toward red as the Eu³⁺ content increased. At 433 K, the Sm³⁺-doped, Eu³⁺-doped, and Sm³⁺/Eu³⁺ co-doped samples retained 119.7%, 93.4%, and 102.3% of their room-temperature integrated emission intensities, respectively. The high thermal stability may be attributed to the structural characteristics of the host, its wide optical band gap, and the temperature-dependent redistribution of Stark and phonon-assisted emission components. A phosphor-converted LED fabricated using Na₃YB₈O₁₅:0.02Sm³⁺,0.01Eu³⁺ and a commercial 400–405 nm, 5 W near-UV LED chip produced multiband emission that partially overlapped with the absorption bands of both chlorophylls and the P_R and P_FR forms of phytochrome. These results suggest that Sm³⁺/Eu³⁺-activated Na₃YB₈O₁₅ is a promising thermally robust, spectrum-adjustable red phosphor for LED applications. Full article

Phenolic resin pyrolytic carbon is a key matrix phase in carbon-based refractories and carbon/carbon composites; however, its defect-rich glassy carbon structure exhibits poor oxidation resistance at elevated temperatures. In this work, we report a facile one-step thermal-treatment strategy using melamine as a nitrogen source to prepare nitrogen-modified phenolic resin pyrolytic carbon (NC). The structural evolution and oxidation behavior of samples carbonized at 500–800 °C were systematically investigated by XRD, SEM, TEM, FT-IR, Raman, XPS, BET, and TG-DSC. The results reveal that melamine-derived nitrogen exists in two distinct forms: at 500–700 °C, a carbon nitride-rich phase consistent with graphitic carbon nitride (g-C₃N₄) forms sheet- and belt-like structures on the carbon surface and partially fills the internal pores; at 800 °C, its long-range crystalline signature disappears, while pyridinic, pyrrolic, and graphitic nitrogen remain in the carbon framework. From 500 to 800 °C, the relative N 1s fraction of pyridinic N decreases from 72.33% to 44.38%, whereas graphitic N increases from 0.47% to 24.09%. Meanwhile, the pore structure evolves from a mesopore-dominated architecture with a limited accessible surface area at 500–600 °C to a micropore-rich structure at 700–800 °C. Relative to unmodified PR-800, NC-800 exhibits an approximately 30 °C higher onset oxidation temperature and an approximately 40 °C higher complete oxidation temperature, together with a lower maximum mass-loss rate and a delayed, broadened exothermic response. These results show that melamine-derived pore regulation and skeletal nitrogen doping jointly retard oxygen transport and suppress oxidation-active defect sites, providing a simple and potentially scalable route for improving the high-temperature oxidation resistance of phenolic resin pyrolytic carbon. Full article

Lanthanide-doped Ca₂Nb₂O₇ offers versatile and tunable luminescence properties. Previous studies have shown that Pr³⁺-doped and Pr³⁺/Er³⁺ co-doped Ca₂Nb₂O₇ ceramics exhibit non-destructive mechanoluminescence, up- and down-conversion luminescence, and thermoluminescence, with potential for optical temperature sensing. However, to date, niobate glass–ceramics (GCs) remain largely unexplored, although they would offer excellent temperature resistance, high chemical durability, controllable crystallization, and the possibility to combine functional properties. This study investigates Pr³⁺ single doping and Pr³⁺/Er³⁺ co-doping in glass–ceramics prepared from niobium-containing calcium aluminosilicate glasses with the composition 55CaO-(35-x)Al₂O₃-10SiO₂-xNb₂O₅ (mol%, where x = 0, 10). The aim is to obtain glass–ceramics containing Ca₂Nb₂O₇ crystals with a layered perovskite structure and to evaluate their suitability as hosts for rare-earth ions. The luminescence properties of both parent glasses and GCs were investigated, and it is shown that the glasses show intrinsic luminescence which, when doped, enables sensitization of rare-earth elements via charge transfer. Furthermore, several interesting photoluminescence mechanisms were observed in the doped GCs, including (i) Er³⁺ up-conversion from the NIR to the visible, (ii) variations in the relative intensities of Er³⁺ hypersensitive transitions, reflecting changes in site symmetry, and (iii) a charge transfer process to the activator ions under UV excitation. These phenomena extend the accessible excitation range for rare-earth emission. Overall, the developed Ca₂Nb₂O₇ GCs demonstrate efficient dopant integration, confirming their suitability as lanthanide hosts for advanced photonic, sensing and energy conversion applications. Full article

Dense Ce,Pr-doped YAG transparent ceramics (YAG:Ce,Pr) with enhanced red emission were fabricated by pressureless sintering in air at 1600 °C. Fine YAG powders containing 0.2 mol% Ce and varying amounts of Pr (0.04–0.32 mol%) were synthesized using a glycine–nitrate combustion method. The emission and excitation spectra were analyzed to investigate the influence of Pr doping on red emission. The results indicate that YAG: Ce,Pr ceramics are a promising candidate for blue-to-yellow light conversion. The strongest red emission component was measured in samples containing 0.16 mol% Pr. It was confirmed that electron transfer from Ce to Pr enhances the red emission component (609 nm), primarily by increasing the population of electrons relaxing from the ¹D₂ excited state to the ³H₄ ground state. Further increasing the Pr concentration beyond 0.16 mol% resulted in a reduction in the red emission intensity due to concentration quenching. Microstructural analysis of YAG:Ce,Pr revealed a dense and homogeneous microstructure composed of equiaxed grains. Full article

This work proposes a simplified HTL-free PSC structure based on Cs₂AgBiBr₆ doped with praseodymium (Pr³⁺). By reducing interfacial layers, this design reduces defect-induced recombination and increases the resistance of the device under environmental stresses (such as temperature, oxygen, and humidity). The performance of the Pr³⁺-doped PSC (Cs₂Ag_0.95Pr_0.05BiBr₆) with both FTO and Tb-FTO as front contacts were investigated using solar capacitance simulation software (SCAPS-1D) version 3.3.10. The FTO-based reference device showed photovoltaic parameters of V_oc = 0.86 V, J_sc = 12.52 mA/cm², FF = 70.13%, and PCE = 7.51%, while the Tb-doped FTO device showed V_oc = 0.86 V, J_sc = 12.67 mA/cm², FF = 72.98%, and PCE = 7.91%. The performance of the device was analyzed based on variation in absorber thickness and defect density, ETL thickness and dopant concentration, band gap, and ETL/absorber interface defect density in the Tb-FTO/TiO₂/Cs₂Ag_0.95Pr_0.05BiBr₆/C to obtain optimal values of 1.0 μm, 10¹³ cm⁻², 0.09 μm, 10²¹ cm⁻², 1.5 eV, and 10⁸ cm⁻³. Utilizing these optimized values, the final device predicted a PCE of 19.93%, FF of 84.51%, J_sc of 27.73 mA/cm², and V_oc of 0.85 V. The device was also found to be sensitive to variations in the back-contact work function, ambient temperature, series and shunt resistances. A PCE of ~27.65% was achieved at higher metal work function (e.g., W_F = 5.9 eV for Se), with a corresponding FF of ~82.69%, J_sc of ~27.78 mA/cm², and V_oc of 1.20 V. Therefore, while direct experimental validation for the proposed HTL-free structure is not yet available, the comparison with experimentally demonstrated HTL-containing counterparts provides confidence in the predictive capability of our model. We expect that the present work will serve as a theoretical foundation and motivation for future experimental fabrication and characterization of HTL-free devices. Full article

Reversible solid oxide cells (ReSOCs) represent one of the most promising electrochemical technologies for sustainable energy conversion and storage, yet their large-scale deployment remains constrained by electrode materials capable of sustaining stable performance under alternating oxidizing and reducing conditions. Reversible solid oxide cells require electrode materials that combine phase stability, chemical compatibility, redox tolerance and a microstructure suitable for gas transport and surface reactions. However, the relationships among cation composition, thermal processing, phase formation and local chemical homogeneity remain insufficiently understood, particularly for compositionally complex perovskite-related oxides. In this work, this problem was addressed through a comparative physicochemical screening of three candidate electrode materials synthesized by a simple co-precipitation route: two co-doped lanthanum ferrites, (La_0.8Sr_1.2) (Fe_0.9Co_0.1)O_6+δ (LSFC) and (La_0.8Ca_1.2) (Fe_0.9Co_0.1)O_6+δ (LCFC), and one high-entropy praseodymium nickelate, Pr(Ba_0.8Ca_0.2)(Fe_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)₂O_6+δ (PBC-HEO). DTA–TG analysis was used to determine the thermal decomposition and crystallization ranges of the precipitated precursors. Phase evolution as a function of calcination temperature was investigated by X-ray diffraction, while Raman and FTIR spectroscopy were employed to examine the local metal–oxygen environment and structural disorder. Raman spectroscopy confirmed the formation of perovskite-type metal–oxygen frameworks in all samples and revealed distinct redistributions of spectral weight between apical/equatorial (or symmetry-related) BO₆ stretching sub-modes and bending/tilting modes, reflecting different local defect-chemical mechanisms associated with A-site doping (Sr vs. Ca) in the Ruddlesden–Popper ferrites and B-site multi-cation occupancy in the double-perovskite PBC-HEO. Bulk and local elemental compositions were assessed by ICP-MS and SEM-EDS, respectively, and SEM was used to compare particle morphology and porosity. SEM-EDS analysis showed that PBC-HEO developed the most open and interconnected microstructure among the investigated powders, although accompanied by residual compositional heterogeneity. This morphology may favor gas accessibility; however, its effective impact on electrocatalytic performance requires dedicated surface area, porosimetry, electrical, and electrochemical measurements. LSFC formed a single major Ruddlesden–Popper phase only after high-temperature calcination, whereas LCFC retained calcium-containing secondary phases. PBC-HEO developed a major perovskite-related phase at 700 °C, accompanied by minor Zn-rich segregation. Under the selected processing conditions, PBC-HEO retained the finest and most interconnected porous microstructure, although it also displayed the highest local compositional heterogeneity. These results demonstrate that cation selection and thermal history jointly control phase stability, local disorder and microstructure, providing a basis for the subsequent electrochemical evaluation and optimization of perovskite-related ReSOC electrode materials. Full article

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air cathodes severely restrict the practical application of rechargeable zinc–air batteries (ZABs). Herein, equimolar lanthanide-doped spinel Co₃O₄ bifunctional electrocatalysts were synthesized via a citric acid-assisted sol–gel method. Among Ce-, Pr-, La-, and Sm-doped catalysts, Sm-Co₃O₄ exhibits the optimal electrocatalytic performance with a high ORR half-wave potential of 0.72 V and superior OER activity with an overpotential of 1.65 V at 10 mA cm⁻², achieving a minimal potential gap ΔE of 0.93 V. Rotating ring-disk electrode (RRDE) measurements and Koutecky–Levich (K–L) analyses confirm the exclusive 4e⁻ ORR pathway. Characterizations reveal that Sm doping modulates the electronic structure and lattice distortion of Co₃O₄, raises the Co²⁺/Co³⁺ ratio (0.59) and creates abundant oxygen vacancies, thereby significantly lowering the overpotentials for both ORR and OER. This study provides new insights for designing high-performance spinel-based bifunctional electrocatalysts for ZABs. Full article

We report a CMOS-compatible ferroelectric memristor based on a TiN/AlScN/n⁺ Si metal ferroelectric semiconductor (MFS) structure, fabricated entirely via low-temperature sputtering processes. The ultrathin AlScN film exhibits robust ferroelectricity with a high remanent polarization (2P_r ≈ 80.91 μC/cm²) and excellent endurance over 10⁵ cycles, while maintaining uniform switching across cells. Notably, the use of a heavily doped silicon bottom electrode enables full compatibility with conventional back-end-of-line (BEOL) CMOS processes and facilitates integration with silicon-based circuits. Beyond stable memory performance, the device demonstrates volatile short-term memory (STM) behavior originating from depolarization field-induced polarization relaxation, which is essential for neuromorphic dynamics. Leveraging this STM feature, the device was implemented as a physical reservoir in a reservoir computing (RC) framework, achieving 97.64% classification accuracy on the MNIST dataset using temporally coded inputs. These results highlight the potential of AlScN-based ferroelectric memristors as dynamic CMOS-compatible building blocks for in-memory and neuromorphic computing. Full article

Temperature-dependent luminescence of Pr³⁺-doped materials was investigated using both conventional luminescence intensity ratio (LIR) and principal component analysis (PCA)-based thermometry. Three host matrices with distinct structural properties, LiLaP₄O₁₂, YNbO₄, and Y₂O₃, were selected to evaluate the influence of crystal structure on thermometric performance. Temperature-resolved emission spectra recorded over the 103–523 K (−170 to 250 °C) range were analyzed using both approaches, with the first principal component (PC₁) serving as a thermometric parameter in the PCA. The results show that crystal symmetry and site multiplicity strongly influence the temperature-dependent spectral evolution and, consequently, the thermometric response. LiLaP₄O₁₂ exhibits stable and well-defined spectral evolution, resulting in balanced thermometric accuracy and resolution. YNbO₄ shows enhanced sensitivity to temperature variations due to increased spectral complexity and stronger crystal-field effects, leading to improved resolution but increased calibration uncertainty. In contrast, Y₂O₃ exhibits reduced thermometric performance due to overlapping emissions from multiple crystallographically inequivalent sites with distinct thermal responses. Compared to LIR, PCA provides improved thermometric figures of merit, particularly in systems with complex and strongly overlapping emission bands, demonstrating the potential of full-spectrum analysis in luminescence thermometry. Full article

Pr³⁺-activated phosphors are promising for non-contact optical thermometry under blue-light excitation. In tantalate hosts, Pr³⁺-Ta⁵⁺ intervalence charge transfer (IVCT) states may introduce thermally activated nonradiative pathways involving the ³P₀ and ¹D₂ levels, thus affecting their thermal quenching behavior and thermometric performance. However, the concentration- and temperature-dependent luminescence of CaTa₂O₆:Pr³⁺ remains unexplored. In this study, CaTa₂O₆:Pr³⁺ phosphors were synthesized via the solid-state reaction method, and a phosphor-in-glass (PiG) composite was fabricated by co-sintering the mixture of the phosphor and the precursor glass (PG) powder. The structural characteristics and the luminescence properties of CaTa₂O₆:Pr³⁺ phosphors under 450 nm excitation were investigated. The IVCT band was confirmed in the excitation spectrum. Optimal Pr³⁺ concentrations were 2 mol% for ³P_J and 0.7 mol% for ¹D₂ emissions. With Pr³⁺/Zr⁴⁺ or Pr³⁺/Sn⁴⁺ co-doping, the emission intensity was enhanced by 1.34 and 1.31 times, respectively. The PiG exhibited similar spectral profiles. An FIR mode based on ³P₁→³H₅/³P₀→³F₂ transitions achieved maximum relative sensitivities of 1.09% K⁻¹ for the phosphor and 1.18% K⁻¹ for the PiG at 298 K. These findings suggest that CaTa₂O₆:Pr³⁺-based materials are potential candidates for luminescence thermometry. Full article

Hafnium oxide thin films have been extensively investigated for high-speed and low-power memory applications. Herein, we investigated the influence of oxygen vacancies and external stress on the ferroelectric characteristics of Al-doped HfO₂ (HfAlO). Compared with HfAlO with 14% oxygen vacancies, films with 21% oxygen vacancies could lower the polarization switching barrier and increase the fraction of the ferroelectric phase. Furthermore, significant external stress promotes ferroelectric phase formation, thereby enhancing ferroelectric characteristics. The remanent polarization achieved with W electrodes (2Pr = 38 µC/cm²) is about 18 times that of Au electrodes, owing to the lower thermal expansion coefficient of W electrodes. Density functional theory calculations and finite element analysis provide theoretical insights corroborating the experimental results, helping to pave the way for developing hafnium-based materials for next-generation in-memory computing applications. Full article

Porous, crystalline gamma-Al₂O₃ coatings with a thickness of (6 ± 0.5) μm and a uniform distribution of rare earth (RE) dopants are synthesized by plasma electrolytic oxidation of aluminum at a current density of 150 mA/cm² in a boric acid and borax (BB) solution containing added RE oxide particles (Ho₂O₃, Tb₄O₇, and Pr₆O₁₁) at concentrations of 1, 2, and 4 g/L. The concentration of RE oxide particles in the BB solution determines the amount of RE elements incorporated into the coatings but does not significantly affect their surface morphology, crystal structure, or light absorption properties. The coatings exhibit high absorption in the middle/near-ultraviolet region, characteristic of Al₂O₃. Typical 4f-4f transitions of Ho³⁺, Tb³⁺, and Pr³⁺ are observed in the photoluminescence spectra. Photocatalytic evaluations using methyl orange degradation under simulated solar irradiation show that RE doping significantly enhances photocatalytic efficiency. Peak degradation efficiencies are achieved at a concentration of 4 g/L for all RE oxides. After 8 h of irradiation, maximum degradation reaches 88%, 92%, and 85% with pseudo-first-order rate constants (k_app) of about 0.274 h⁻¹, 0.339 h⁻¹, and 0.232 h⁻¹ for coatings synthesized in BB with 4 g/L Ho₂O₃, Tb₄O₇, or Pr₆O₁₁, respectively. In comparison, the pristine Al₂O₃ coating achieves only about 50% degradation (k_app ≈ 0.087 h⁻¹). Photoluminescence indicates that RE³⁺ ions serve as effective charge-carrier traps, suppressing electron–hole pair recombination. RE-doped Al₂O₃ coatings demonstrate exceptional structural stability and reusability over six cycles, highlighting their potential for sustainable wastewater remediation. Full article

To optimize the oxygen reduction reaction activity and long-term stability of the PrBaFe₂O_6-δ (PBF) cathode for protonic ceramic fuel cell (PCFC), this study employed the sol–gel method to dope Sc at the Fe-site of PBF, preparing a novel PrBaFe_1.8Sc_0.2O_6-δ (PBFS) cathode. The effects of different sintering temperatures on the phase composition, microstructure, and electrochemical performance of the PBFS cathode were systematically studied. Results showed that the PBFS cathode sintered at 1000 °C formed a single cubic perovskite structure, exhibiting excellent chemical compatibility with the electrolyte. Sc doping induced Fe in the cathode to exhibit a mixed valence state of Fe²⁺/Fe³⁺/Fe⁴⁺, thus significantly increasing the oxygen vacancy concentration. The single cell assembled achieved a peak power density of 1.303 W·cm⁻² and a polarization resistance as low as 0.035 Ω·cm² with H₂ as the fuel at 700 °C. Moreover, after 100 h of long-term operation at 650 °C, the power density decayed by only 5.23%, thus demonstrating excellent long-term stability. This study offers an efficient cobalt-free cathode candidate for PCFC. Full article

The effect of Mn addition on the structural, dielectric, ferroelectric, and mechanical properties of Bi_0.5Na_0.5TiO₃ (BNT) and 0.94(Bi_0.5Na_0.5TiO₃)–0.06(BaTiO₃) (BNT–BT) ceramics was systematically investigated under identical processing conditions. Powders were calcined at 750 °C for 2 h and 900 °C for 2 h, followed by sintering at 1060 °C for 5 h. Mn contents of 0.5 and 5 mol% were selected to represent low-level substitution and near-saturation regimes. XRD confirmed single-phase perovskite formation within laboratory detection limits, while Raman spectroscopy revealed Mn-induced lattice distortions. Low Mn addition (0.5 mol%) enhanced densification and improved remanent polarization in BNT–BT (Pr = 33.5 μC/cm²). In contrast, 5 mol% Mn promoted grain coarsening, increased porosity, and reduced functional performance. Mechanical properties evaluated using two-parameter Weibull statistics showed composition-dependent variations in characteristic hardness and elastic modulus. The results demonstrate that Mn-doping effects depend strongly on both dopant concentration and host-lattice structural state, distinguishing beneficial substitution from defect-saturation behavior in lead-free BNT-based ceramics. Full article

Developing efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) is critical for advancing clean and sustainable energy technologies. Herein, a Fe-doped perovskite oxide Ba_0.7Pr_0.3Co_0.8Fe_0.2O_3−δ (BPCF_0.2) was successfully synthesized via the sol–gel method. By regulating the stoichiometric ratio of precursors and calcination temperature, a stable single-phase perovskite structure was achieved. X-ray photoelectron spectroscopy (XPS) analysis indicated that Fe incorporation increased the proportion of high-valent Co species and lattice oxygen content, which respectively reduced the charge transfer resistance of BPCF_0.2, thereby significantly enhancing catalytic performance. Electrochemical measurements revealed that BPCF_0.2 exhibited remarkable HER activity in 1.0 M KOH, achieving an overpotential of 172 mV at a current density of 10 mA cm⁻², with no significant decay during 200 h of continuous HER testing at 100 mA cm⁻². These results demonstrate that the Fe doping strategy can effectively optimize the electronic structure, providing valuable insights for the development of perovskite-based HER catalysts. Full article