Two new cerium-doped mixed-anion elpasolite scintillators: Cs2NaYBr3I3 and Cs2NaLaBr3I3

We recently discovered that mixed-anion Br–I elpasolite scintillators, Cs₂NaYBr₃I₃: Ce and Cs₂NaLaBr₃I₃: Ce, have promising performance. Ce concentration of these compounds was optimized in terms of light yield. Cs₂NaLaBr₃I₃ with 5% Ce (by mole) has a light yield of 58,000 ph/MeV, and excellent energy resolution of 2.9% at 662 keV. It is better than both endpoint compounds of the Br–I solid solution. Cs₂NaYBr₃I₃ with 2% Ce doping shows energy resolution of 3.3% at 662 keV, despite a relatively modest light yield of 43,000 ph/MeV. Non-proportionality of the mixed Br–I compounds was measured using gamma ray sources ranging in energy from 14 keV to 835 keV.The electronic band gaps of undoped Cs₂NaLaBr₃I₃ and Cs₂NaYBr₃I₃ were determined from optical transmittance and absorbance measurements. The band gaps of the compounds are 4.4 ± 0.1 eV, and 4.3 ± 0.1 eV, respectively.The crystal structures of Cs₂NaLaBr₃I₃: Ce and Cs₂NaYBr₃I₃: Ce are tetragonal and cubic respectively. The high symmetry leads to fewer cracks during crystal growth and minimizes light scattering at grain boundaries. The ease of crystal growth is promising for the scale-up of the growth process to larger sizes.     

High magneto-optical performance of GdFeO3 thin film with high orientation and heavy Ce3+ doping

In this paper, GdFeO₃ thin films with high orientation and heavily Ce³⁺ doping were deposited by radio frequency magnetron sputtering with a matching substrate. The effects of substrates and Ce³⁺ doping on the structure, magnetic and magneto-optical properties of thin films were investigated. As a result, Ce³⁺ doping can not only increase the saturation magnetization but also greatly enhance the magnetic circular dichroism signals of Ce:GdFeO₃ thin films. Based on the density functional theory calculation, it can be found that the probability of electron transition between Ce³⁺ 4f and Fe³⁺ 3d and the difference in the absorption of right and left circularly polarized light increase, which results in the strong magneto-optical effect of Ce:GdFeO₃/STO thin films.     

Quantum confinement and size effects in Cu2ZnSnS4 thin films produced using solution processed ultrafine nanoparticles

Copper–zinc–tin-sulfide (Cu₂ZnSnS₄, abbreviated as CZTS) is a direct band gap p-type semiconductor material with high absorption coefficient. Using oleylamine as solvent/stabilizing agent and metal chlorides and sulfur particles as chemical precursors, CZTS based nanoparticles were produced and subsequently deposited as thin films on glass substrates via spin coating of the nanoinks. The effect of temperature on crystallite size and phase composition was assessed after the solution mixture was undercooled by 30, 70 or 90 °C. Upon cooling the solution from 230 to 140 °C i.e. by 90 °C, maximum refinement in the nanoparticles size was noticed with average size on the order of few nanometers. The morphological and compositional studies of the nanoparticles were performed by means of scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy techniques. Phase-pure CZTS formation was confirmed from fast Fourier transform (FFT) patterns and lattice fringes observed during HR-TEM examination. Characterization of the annealed spin coated films, made from nanoink containing ultrafine nanoparticles, indicated morphological changes in the film surface during air annealing at 350°C that can be attributed to depression of CZTS phase decomposition temperature. Spectrophotometric studies of the annealed films suggested quantum confinement effect through an associated increase in the band gap value from 1.34 to 2.04 eV upon reduction in the nanoparticle size caused by increasing the degree of undercooling to 90 °C.     

Electrochemical properties and thermal neutral state of solid oxide fuel cells with direct internal reforming of methane

Solid oxide fuel cells (SOFCs) with direct internal reforming (DIR) provide a promising method to realize clean and efficient utilization of hydrocarbon fuels. Thse endothermic reforming reactions occur simultaneously with exothermic electrochemical reactions at the anode, making thermal neutral state achievable inside a fuel cell, providing reference to the thermal management. In this study, a calculation model combining experimental data and thermodynamic results was established, validating the possibility of achieving thermal neutral state in DIR-SOFCs. In the process of modeling, the electrochemical and thermodynamic characteristics in direct internal steam and dry reforming were elaborately compared, contributing to a more scientific understanding of anode reaction mechanism. Detailed experimental investigation was carried out to determine the influence of H₂O/CO₂ on the electrochemical properties of DIR-SOFCs, based on which the optimum steam-carbon ratio (S/C) and CO₂ to CH₄ ratios were obtained. Besides, analysis of distribution of relaxation times (DRT) combined with elementary reactions in CH₄H₂O and CH₄CO₂ atmospheres were proposed to distinguish different physical and chemical processes within anodes. The results of this study can be conducive to a more precise understanding of reaction mechanism on SOFC anodes and meaningful for practical application of DIR-SOFCs.     

Effect of Fe2O3 doping on color and mechanical properties of dental 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, iron(III) oxide (Fe₂O₃)-doped zirconia (3Y-TZP) ceramics with desirable mechanical and color properties for dental restorations were fabricated by stereolithography-based additive manufacturing. Six zirconia ceramic paste specimens with high solid loading (58 vol%) and reasonably low viscosity were prepared according to doped content of Fe₂O₃ (0–0.14 wt%). Zirconia ceramics were fabricated using commercial stereolithography three-dimensional printer and sintered at 1500 °C for 4 h to obtain final dense parts with a relative density of above 99%. Effects of Fe₂O₃ doping on microstructure, mechanical properties, and color of 3Y-TZP ceramics were investigated. Results indicate that Fe₂O₃ exhibited little effect on the shrinkage and density of colored ceramics compared to uncolored ceramics. Average grain size of 3Y-TZP ceramics sintered at 1500 °C increased with increasing content of Fe₂O₃. X-ray diffraction analysis showed that tetragonal phase was dominant phase structure of white and colored 3Y-TZP ceramics, and monoclinic phase increased with increasing Fe₂O₃ content. Compared to uncolored specimens, Fe₂O₃ exhibited negative effects on three-point flexural strength (mean > 879.70 MPa), Vickers hardness (mean > 12.14 GPa), and indentation fracture toughness (mean > 4.23 MPa m^1/2) of the colored specimens. With the increase in the content of Fe₂O₃ from 0 to 0.14 wt%, L* (black–white index) value decreased from 83.39 to 79.54, a* (green–red index) value increased from −2.28 to −0.74, and b* (blue–yellow index) value increased from 1.15 to 17.94. Chromaticity (L*, a*, b*) fell within the range of natural tooth color, indicating that it is suitable for dental application because of its color compatibility with natural teeth. In addition, the transmittance slightly decreased with increasing Fe₂O₃ content. Thus, Fe₂O₃-doped 3Y-TZP ceramics can be used as potential candidates for aesthetic dental restoration materials.     

Effects of MgO and Fe2O3 additives on the microstructure and fracture properties of aluminium titanate flexible ceramics

Aluminium titanate (Al₂TiO₅, AT) flexible ceramics were prepared from Al₂O₃–TiO₂ powder system with MgO and Fe₂O₃ as additives through solid-state method. The effects of addition level of MgO and Fe₂O₃ on phase compositions, sintering behavior, microstructure and fracture properties of AT flexible ceramics were systematically investigated. The experimental results show that the introduction of additives can promote the formation of AT and improve the densification by forming solid solution. The addition of MgO could effectively refine AT grains since the formed MgAl₂O₄ spinel grains could pin at the AT grain boundary and inhibit the growth of AT grains. Conversely, the addition of Fe₂O₃ could promote the AT grain growth. And the simultaneous addition of MgO and Fe₂O₃ is beneficial to develop elongated rod-like AT grains. With that, the improved fracture properties can be obtained. Due to pining effect of spinel and better densification, the flexural strength of modified AT flexible ceramics is about 34 times higher than that of virgin. In addition, thanks to the microcracked structure and high grain aspect ratio, events of crack deflection, crack branching, grains pull-out and grains bridging are more likely to occur, leading to an increase in the flexibility by about 133%.     

Highly transparent polycrystalline Gd2O3 ceramic attained via ZrO2 stabilization effect

The transition from the cubic to monoclinic phase of Gd₂O₃ at high temperatures poses a significant challenge to the preparation of transparent Gd₂O₃ materials. In this work, we presented a straightforward yet effective method for fabricating transparent Gd₂O₃ ceramics. Via ZrO₂ stabilization effect for phase structure, highly transparent Gd₂O₃ ceramics were successfully fabricated by vacuum sintering at 1850 °C for 8 h. The effect of different Zr (0 ∼ 13 at%) concentrations on phase transition, grain growth, fracture mode and optical properties of Gd₂O₃ transparent ceramics was investigated. As the Zr content increases, the transition from the cubic (C) to monoclinic (M) phase is effectively suppressed, which is crucial for achieving Gd₂O₃ transparent ceramics. Moreover, the results indicate that the addition of ZrO₂ has a significant effect on grain growth by not only impeding the migration of grain boundaries but also affecting the phase composition. In addition, the 11 at% Zr-doped Gd₂O₃ ceramic exhibits the best optical properties, of which transmittance is about 76% at 850 nm and about 80% in the 2.5 µm ∼ 6 µm mid-infrared range. This work provides an illustrative example for the development of other ceramics with phase transition. The obtained Zr-doped Gd₂O₃ transparent ceramics with high optical quality are potential candidates for optical window, scintillator host and mid-infrared transmission materials.     

Antibacterial effects of biosynthesized silver nanoparticles using aqueous leaf extract of Rosmarinus officinalis L.

In this study, we demonstrate a green approach for the synthesis of silver nanoparticles (AgNPs) using aqueous leaf extract of Rosmarinus officinalis under ambient conditions. The uniqueness of this method lies in its rapid synthesis within 15 min. The synthesized AgNPs were characterized using UV–vis, FTIR, XRD, FE-SEM coupled with EDX, TEM and AFM. The synthesized particles were found to be 14.20–42.42 nm with face centered cubic geometry. The functional group of flavonoids and terpenoids was largely identified by FTIR which was found to be responsible for the synthesis and stabilization of the AgNPs. Further, antibacterial efficacy of the biologically synthesized AgNPs was investigated by the standard method against Pseudomonas aeruginosa and Staphylococcus aureus. The results showed that the aqueous leaf extract mediated synthesized AgNPs is an excellent antibacterial agent against clinical pathogens.     

Luminescence and energy transfer in Er3+/Nd3+ ion-codoped Ge–In–S–CsBr chalcohalide glasses

This study investigates the emission properties of the Er³⁺/Nd³⁺ ions codoped 70GeS₂–10In₂S₃–20CsBr chalcohalide glasses. The vacuumed melt-quenching technique is employed to synthesize the glasses. The absorption spectra, upconversion and near-IR emission spectra as well as fluorescence decay curves are collected. With the increasing concentration of Er³⁺ ions, the lifetimes at 1073 nm for Nd³⁺ ions decrease from 538 to 420 μs under 808 nm excitation. Meanwhile, the lifetimes at 1540 nm for Er³⁺ ions decrease from 245 to 214 μs with the increasing concentration of Nd³⁺ ions. The emission spectra and lifetimes show that energy transfer exists between the Nd³⁺ and Er³⁺ ions. The luminescence and detailed energy transfer mechanisms are schematically proposed.     

Optical properties of Yb-doped ZnO/MgO nanocomposites

Yb³⁺ doped ZnO/MgO nanocomposite were prepared by combustion synthesis method. The samples were further heated to 1000 °C to improve their crystallinity and photoluminescent efficiency. The concentrations of Yb³⁺ and Mg²⁺ were varied between 1–2% and 5–70% respectively in prepared samples. The nano-powders were characterized by Scanning Electron Microscopy and X-ray Diffraction for morphology and structural determination. XRD studies have revealed the wurtzite structure for Mg_xZn_1−xO for Mg concentrations below 30%. Higher concentrations of Mg results in Yb³⁺ doped ZnO/MgO nanocomposite containing three phases; the wurzite hexagonal phase typical of ZnO, the cubic phase of MgO and a small amount of cubic Yb₂O₃ phase. As expected, the amount of cubic phase in nano-powders increased with the increase of Mg concentration in ZnO. The crystallite size of ZnO/MgO composites decreased from 55 nm to 30 nm with increase of Mg content. SEM images of Yb³⁺ doped ZnO/MgO nanocomposite with higher Mg content (>50%) showed clearly distinct hexagonal and cubical shaped nano-particles. Photoluminescent emission showed a broad band in the range (435 nm to 700 nm). Pure ZnO nano-phosphor showed an emission peak around 545 nm, which is blue shifted with Mg content. The photoluminescence intensity increased with increase of Mg content in ZnO and it became maximum with 30% Mg concentration. Time resolved decay curves of photoluminescence indicated decay time in microsecond time scale.