Mn2+/Mg2+ co-doped AlON ceramic with ultra-narrowband green emission combining high transparency toward a wide gamut backlight application.

Narrowband green-emission, combined with superior physicochemical stability and thermal performance, is regarded as a common pursuit in backlight display applications. However, mainstream phosphor-converted materials composed of resin or silicone resin easily encounter the dilemma of thermal decomposition and chemical corrosion for practical use. To overcome this problem, in this work, Mn2+/Mg2+ co-doped AlON ceramic is successfully realized with ultra-narrowband green-emission and high transparency. The luminescent property of AlON: Mn2+-Mg2+ ceramic exhibits narrowband green emission centered at 509 nm with a full width at half maximum of 36 nm, which is smaller than the corresponding powder counterpart (44 nm). Moreover, AlON: Mn2+-Mg2+ ceramic presents a wide color gamut (103.6%) and high color purity (74%). Concurrently, high transmittance of this ceramic, at 82%, unveils a potential innovation in the display technology field. This work may facilitate the development of narrowband green light-emitting converters based on AlON: Mn2+-Mg2+ transparent ceramics in large color gamut backlight display applications.

Decolorization, spectral broadening, and luminescence enhancement in Tb:Y2O3 transparent ceramics through vacuum thermal reduction.

Tb3+ is extensively employed in magneto-optical devices and luminescent materials owing to its distinctive physical properties. However, under certain conditions, trivalent Tb3+ readily undergoes oxidation to tetravalent Tb4+, significantly reducing the performance of devices containing Tb3+. In this Letter, we report a technique called dual-annealing (DA) post-treatment, which effectively solves Tb oxidation issues by utilizing the reducibility of the vacuum environment. High-quality Tb:Y2O3 transparent ceramics were prepared with in-line transmittance of ∼80% at 800 nm. Subsequently, the prepared ceramics were subjected to DA treatment. The optical, photoluminescence, radioluminescence, and x-ray imaging properties of DA samples were comprehensively compared with those of conventionally single-annealed (SA) samples. The coloration of Tb:Y2O3 transparent ceramics due to Tb4+ absorption was eliminated by DA. Notably, the DA sample showed a 3.28-fold increase in photoluminescence intensity and a 2.73-fold increase in radioluminescence intensity compared with the traditional SA sample. DA post-treatment enables Tb: Y2O3 transparent ceramics to achieve x-ray imaging capabilities. This Letter presents a simple, efficient, and universally applicable post-treatment technique expected to replace conventional hydrogen annealing in numerous scenarios.

Ultrapure single-band red upconversion luminescence in Er3+ doped sensitizer-rich ytterbium oxide transparent ceramics for solid-state lighting and temperature sensing.

Achieving single-band upconversion (UC) is a challenging but rewarding approach to attain optimal performance in diverse applications. In this paper, we successfully achieved single-band red UC luminescence in Yb2O3: Er transparent ceramics (TCs) through the utilization of a sensitizer-rich design. The Yb2O3 host, which has a maximum host lattice occupancy by Yb3+ sensitizers, facilitates the utilization of excitation light and enhances energy transfer to activators, resulting in improved UC luminescence. Specifically, by shortening the ionic spacing between sensitizer and activator, the energy back transfer and the cross-relaxation process are promoted, resulting in weakening of green energy level 4S3/2 and 2H11/2 emission and enhancement of red energy level 4F9/2 emission. The prepared Yb2O3: Er TCs exhibited superior optical properties with in-line transmittance over 80% at 600 nm. Notably, in the 980nm-excited UC spectrum, green emission does not appear, thus Yb2O3: Er TCs exhibit ultra-pure single band red emission, with CIE coordinates of (0.72, 0.28) and color purity exceeding 99.9%. To the best of our knowledge, this is the first demonstration of pure red UC luminescence in TCs. Furthermore, the luminescent intensity ratio (LIR) technique was utilized to apply this pure red-emitting TCs for temperature sensing. The absolute sensitivity of Yb2O3: Er TCs was calculated to be 0.319% K-1 at 304 K, which is the highest level of optical thermometry based on 4F9/2 levels splitting of Er3+ known so far. The integration between pure red UC luminescence and temperature sensing performance opens up new possibilities for the development of multi-functional smart windows.

Fabrication and Supercritical Water Corrosion Resistance of TiN/TiNC/Al2O3 Multilayer Coating on Inconel 625 Alloy by CVD Method.

A TiN/TiNC/Al2O3 multilayer coating was deposited on an Inconel 625 alloy by the chemical vapor deposition method as a protective barrier to improve the corrosion resistance in supercritical water. The corrosion characteristics were evaluated in a reactor at 500 °C and 25 MPa for 72 h. The surface morphology of the coated samples was relatively dense with no obvious cracks or pores observed. The XRD analysis revealed that the coatings were composed of TiN, TiNC and α-Al2O3 phases. After exposure to supercritical water, the surface morphology of the coatings was still dense and kept integrity. The phase composition of the coatings was also not changed, with no obvious corrosion scales detected. This result demonstrates the effectiveness of TiN/TiNC/Al2O3 coatings as a protective coating under harsh supercritical water environments.

Sol-Gel-Derived Ni3Al Coating on Nickel Alloy for Oxidation Resistance in Supercritical Water Environments.

Although nickel-based alloys are widely used in industries due to their oxidation and corrosion resistance, the pursuit of better performance in harsh environments is still a great challenge. In this work, we developed a sol-gel method to synthesize Ni3Al coating on a nickel alloy, assisted by a post-annealing process, and investigated the oxidation-resistant performance. The coating thickness can be controlled by designing the deposition times, which keep the pure Ni3Al phase stable. In addition, the surface morphologies indicate that the coating is compact without obvious voids or cracks. Furthermore, the oxidation-resistant property of the coating was investigated by carrying out a supercritical water oxidation experiment. The crystalline structure and surface morphology of the samples before and after 72-h oxidation demonstrated the superior oxidation resistance of the coating. This work provides a convenient method to fabricate an oxidation-resistant coating on a nickel-based alloy, which would be significant for prolonging the service life of vessels under oxidation conditions, especially for supercritical water reactions.

Defect Regulation of Terbium-Doped Y2Zr2O7 Transparent Ceramic for Wide-Range Multimode Tunable Light-Shielding Windows.

In the most promising new window materials, the light-blocking property of the state-of-the-art transparent polycrystalline ceramics is still located in the UV range, which undoubtedly limits their applications. Herein, a transparent Y2Zr2O7:Tb (YZO:Tb) ceramic for light-shielding windows was prepared by a solid-state reaction and vacuum sintering method. Two simple and efficient routes, with doping concentrations varying and air-annealing temperatures regulating, were developed for the first time to control the content of defect clusters [TbY4+-O2--TbY4+] and [TbY4+-e•], enabling the optical cutoff waveband of these ceramics spanning from UV and BV to green light. These defect clusters generated from an air-annealing process were proposed for the relevant reaction mechanisms concerning light erasure behavior. The controllably tailoring of optical cutoff wavelength from Tb single-doped YZO ceramics, adjusted by defect clusters, may open a novel door to develop lanthanide-doped transparent ceramics for wide-range tunable light-shielding windows.

Uranium-Incorporated Pyrochlore La2(UxMgxZr1-2x)2O7 Nuclear Waste Form: Structure and Phase Stability.

As efficient and stable nuclear waste forms, single-phase uranium (U6+)-incorporated La2Zr2O7 nanoparticles were designed and synthesized in an air atmosphere. To obtain a high U loading, divalent magnesium (Mg2+) was introduced to balance the extra charge from the substitution of tetravalent zirconium (Zr4+) by U6+ with a minimized impact to the lattice. There is a composition-driven phase transition from order pyrochlore to defect fluorite as the U concentration increases from 10 to 30 mol %, demonstrating both good solubility and stability of the La2Zr2O7 host for U and potentially for other actinides. La2(UxMgxZr1-2x)2O7 (x = 0-0.3) nanoparticles showed good dispersity and crystallinity with an average particle size of ∼48 nm. Furthermore, X-ray photoelectron spectroscopy, Raman spectroscopy, and emission spectroscopy revealed that U was stabilized in the hexavalent state in the form of a UO22+ ion. Spectroscopic methods also demonstrated that our samples caused a scintillating response with an orange emission (597 nm) by 230 nm excitation. In addition, density functional theory simulations were employed to investigate the atomic structures and electronic properties of the U-incorporated pyrochlores. The calculated bond lengths, atomic charges, and charge density confirm the existence of UO22+ ions. Supported by both experimental and computational results, a novel geometrical structure was proposed to explain the Mg2+-U6+ substitution. This work demonstrated the successful development of U-incorporated La2Zr2O7 nanoparticles and provided an efficient way to immobilize U in these ceramic waste matrixes.

First-principles study of the effect of dopants (Pd, Ni) on the formation and desorption of T2O from a Li2TiO3 (001) surface.

We investigated the effect of Pd and Ni dopants on the formation and desorption of tritiated water (T2O) molecules from the Li2TiO3 (001) surface using first-principles calculations coupled with the climbing-image nudged elastic band method. We calculated the energy barriers for T2O production and desorption on the pure Li2TiO3 surface to be 0.94 and 0.64 eV, respectively. The Pd and Ni dopants enhanced T2O formation by reducing the formation energy of O vacancies, and T2O generated spontaneously on the dopant surface. Moreover, we found that dopant atoms affect the charge transfer of neighboring atoms, which leads to orbital hybridization and the generation of a chemical bond between the O and T on the doped Li2TiO3 surface. In addition, desorption of T2O from the doped Li2TiO3 surface requires a relatively low energy (<0.50 eV). This theoretical study suggests that doping the Li2TiO3 surface with metal atoms is an effective strategy for producing T2O molecules and is beneficial to T release.

Optimization of the Amount and Molecular Weight of Dispersing Agent PEG During the Co-Precipitation Preparation of Nano-Crystalline C-YSZ Powder.

Single-phase nano-crystalline yttria-stabilized zirconia (YSZ) powder was prepared by co-precipitation method using zirconium oxychloride (ZrOCl2 · 8H2O) and yttrium nitrate (Y(NO3)3 · 6H2O) as raw materials and ammonium bicarbonate (NH4HCO3) and liquor ammonia (NH4OH) as the precipitators. In order to get the powder with favorable dispersibility, polyethylene glycol (PEG, HO(CH2CH2O) n H) with different molecular weights and amounts was used as a dispersant agent in the synthesis process and its effects on the YSZ powder was investigated. The scanning electron micrograph (SEM) images showed that the degree of agglomeration and the mean crystal size of YSZ powder varied with the amount and the molecular weight of PEG. The appropriate amount and molecular weight of PEG were given by comparing the dispersibility and crystal size distribution of powders. In the process, one also could find that the promotion of dispersion was insensitive to the molecular weight, and all PEG (400­2000) can exert an ability to reduce the agglomeration. The proper amount of PEG400, PEG600, PEG1000, PEG2000 was 3 wt%, 3 wt%, 2 wt%, 2 wt%, respectively. The transmission electric microscope studies in conjunction with the XRD analyzes verified the low degree of agglomeration and the size of YSZ powder varied between 10~20 nm.

Fast crystallization of amorphous Gd2Zr2O7 induced by thermally activated electron-beam irradiation.

We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd2Zr2O7 synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd2Zr2O7 and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase. Fast crystallization could be induced by 120 keV e-beam irradiation (beam current = 0.47 mA/cm2). The crystallization occurred on the nanoscale upon ionization irradiation at 400 °C after a dose of less than 1017 electrons/cm2. Under e-beam irradiation, the activation energy for the grain growth process was approximately 10 kJ/mol, but the activation energy was 135 kJ/mol by calcination in a furnace. The thermally activated ionization process was considered the fast crystallization mechanism.

Constructing three-dimensional (3D) nanocrystalline models of Li4SiO4 for numerical modeling and simulation.

The three-dimensional (3D) nanocrystalline models of lithium silicates with the log-normal grain size distribution are constructed by constrained Voronoi tessellation. During evolution process, the algorithm is improved. We proposed a new algorithm idea by combining Genetic Algorithm (GA) with Least Square (LS) method to make up for the disadvantages of traditional genetic algorithm which may be easily trapped in local optimal solution. In the process of modeling, it is the first time, to the best of our knowledge, that we keep the whole sample showing the charge neutrality by deleting the excess atoms on the polyhedron boundary during the modeling. By using the molecular-dynamics method, the relaxation procedure of nanostructured Li4SiO4 is carried out. The results show that the average mass density of the sample is slightly lower than the experimental data of the perfect crystal after relaxation process. In addition, boundary component proportion (BCP) and density reduction proportion (DRP) of the sample is obtained, respectively. The present results display a significantly reduced BCP but an increased DRP when increasing the mean grain size of the sample.

Modeling multiscale evolution of numerous voids in shocked brittle material.

The influence of the evolution of numerous voids on macroscopic properties of materials is a multiscale problem that challenges computational research. A shock-wave compression model for brittle material, which can obtain both microscopic evolution and macroscopic shock properties, was developed using discrete element methods (lattice model). Using a model interaction-parameter-mapping procedure, qualitative features, as well as trends in the calculated shock-wave profiles, are shown to agree with experimental results. The shock wave splits into an elastic wave and a deformation wave in porous brittle materials, indicating significant shock plasticity. Void collapses in the deformation wave were the natural reason for volume shrinkage and deformation. However, media slippage and rotation deformations indicated by complex vortex patterns composed of relative velocity vectors were also confirmed as an important source of shock plasticity. With increasing pressure, the contribution from slippage deformation to the final plastic strain increased. Porosity was found to determine the amplitude of the elastic wave; porosity and shock stress together determine propagation speed of the deformation wave, as well as stress and strain on the final equilibrium state. Thus, shock behaviors of porous brittle material can be systematically designed for specific applications.

Unique mechanical properties of nanostructured transparent MgAl2O4 ceramics.

Nanoindentation tests were performed on nanostructured transparent magnesium aluminate (MgAl2O4) ceramics to determine their mechanical properties. These tests were carried out on samples at different applied loads ranging from 300 to 9,000 µN. The elastic recovery for nanostructured transparent MgAl2O4 ceramics at different applied loads was derived from the force-depth data. The results reveal a remarkable enhancement in plastic deformation as the applied load increases from 300 to 9,000 µN. After the nanoindetation tests, scanning probe microscope images show no cracking in nanostructured transparent MgAl2O4 ceramics, which confirms the absence of any cracks and fractures around the indentation. Interestingly, the flow of the material along the edges of indent impressions is clearly presented, which is attributed to the dislocation introduced. High-resolution transmission electron microscopy observation indicates the presence of dislocations along the grain boundary, suggesting that the generation and interaction of dislocations play an important role in the plastic deformation of nanostructured transparent ceramics. Finally, the experimentally measured hardness and Young's modulus, as derived from the load-displacement data, are as high as 31.7 and 314 GPa, respectively.

Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature.

We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400°C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900°C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material.

[Raman spectra analysis of bromine doped hydrogenated amorphous carbon (a-C : Br : H) films deposited by RF-PECVD].

Bromine doped hydrogenated amorphous carbon (a-C : Br : H) thin films were deposited on silicon wafers by rf. -plasma enhanced chemical vapor deposition (RF-PECVD) with a frequency of 13.56 MHz at room temperature using pure bromoethane as a precursor of carbon source mixed with hydrogen (H2) as a carrier gas. The structures of the films prepared by partial pressure of mixed gas (C2 H5 Br/H2) were studied by Raman spectroscopy. The results indicate that the intensity of the Raman D peak is stronger, the Raman G peak positions shift up a little, and the value of I(D)/I(G) increases from 1.18 to 1.36, if the gas pressure of mixed C2 H5 Br/H2 is reduced gradually from 20 to 5 Pa. Meanwhile, the growth of thin film turns gradually into low energy mode promoting the transform of sp2-C from chains to rings.