Densification of zirconia doped yttria transparent ceramics using co-precipitated powders

Ho:Y₂O₃ ceramics were prepared using co-precipitated powders, with ammonium sulfate as dispersant. Y³⁺ was co-precipitated together with Ho³⁺ and Zr⁴⁺ to produce precursors, which were calcined at 1100–1400 °C to produce yttria-based powders. At calcination temperatures of ≤1300 °C, agglomeration of powders was not observed. When the temperature was increased to 1400 °C, severe agglomeration was detected. Densification was closely related to the calcination temperature: a lower calcination temperature resulted in a faster densification of ceramics to the relative density of 99.7%. The ultimate densification to ~100% was also closely related to powders' impurity level and agglomeration. Grain growth was mainly determined by sintering temperature, but not by the initial crystallite size of powders. The optimal calcination temperature was 1300 °C, at which the obtained Ho:Y₂O₃ powder was free from agglomeration. Using this powder, the resultant Ho:Y₂O₃ ceramics showed pore-free microstructure and good optical transparency.     

White luminescence of bismuth and samarium codoped Y2O3 phosphors

In this work Sm³⁺ (0–2.0 at%) and Bi³⁺ (0–2.0 at%) doped Y₂O₃ luminescent powders were prepared by a sol–gel method from yttrium acetylacetonate, samarium and bismuth nitrates as metal sources. The as prepared powders (chemical composition is close to stoichiometric Y₂O₃) present the cubic structure from 700 °C, and at 900 °C are characterized by the presence of rounded particles with heterogeneous size of 42.9 nm. Luminescent effect of ions of Sm³⁺ and Bi³⁺ into Y₂O₃ host as was studied on heat treated powders from 800 to 1100 °C. The combination of the red luminescence from the Sm³⁺ ions and the bluish from Bi³⁺, makes the synthesized phosphors candidates to be used in fabrication of phosphor-converted light-emitting diodes (LEDs).     

Preparation and Characterization of CIGSe Solar Cells by Ink Printing on Alumina Substrates with Self‐Synthesized Selenide Powders via an Environment‐Friendly and Cost‐Effective Dry Synthesis Route

CIGSe solar cells with an ink‐printing absorber layer were prepared on Mo‐coated alumina substrates. The use of alumina substrates can extend the process window to higher temperatures. The inks contained single‐phase CIGSe powder, which was formed by firing different selenide powders of Cu₂Se, In₂Se₃, and Ga₂Se₃ at 800°C. All these powders were synthesized with an environment‐friendly and cost‐effective powder process. The printed inks were sintered at 600–800°C. The solar cells had power conversion efficiency of 0.50%, an open‐circuit voltage of 27 mV, a short‐circuit current density of 37 mA/cm², and a fill factor of 0.50.     

Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO₂ and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin^?1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar⁺-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO₂ was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.     

Translucent Yttria‐ and Silica‐Doped Mullite Ceramics with Anisotropic Grains Produced by Spark Plasma Sintering

Translucent, high‐performance, mullite ceramics with anisotropic grains were prepared by the spark plasma sintering (SPS) of a powder mixture consisting of commercial mullite powder, which already contained small amounts of alumina (θ and α) and silica (cristobalite) (≤3 wt% in total), to which 2 and 1 wt% of yttria and amorphous silica was admixed, respectively. The combination of low‐viscosity Y₂O₃–Al₂O₃–SiO₂ transient liquid formation and SPS sintering provided enhanced densification, also provoking anisotropic grain growth (which became exaggerated after 20 min of SPS dwell time), at a relatively low sintering temperature of 1370°C. In this way, it was possible to meet the conflicting demands for obtaining a dense mullite ceramic with anisotropic grains, ensuring good mechanical properties, while preserving a noticeable light transmittance. In terms of mechanical and optical properties, the best results were obtained when SPS dwell times of 5 and 10 min were employed. The as‐sintered samples possessed densities in the range 3.16–3.18 g/cm³, anisotropic grains with an aspect ratio (AR) of 7 and a grain thickness of approximately 0.45 μm, a flexural strength between 350 and 420 MPa, a Vickers indentation toughness and a hardness of approximately 2.45 MPa·m^1/2 and 15 GPa, respectively, and an optical transmittance of between 30% and almost 50% in the IR range.     

Effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives for microelectronic applications

The effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives are investigated. Silver‐coated copper powders with spherical and flake‐shaped particles were oxidized at temperatures of 30°C, 175°C and 240°C for two hours and dispersed in an epoxy matrix. As silver‐coated copper powders are oxidized at 30°C and 175°C, the critical volume fractions of the conductive adhesives are slightly affected by oxidation and particle shape at these temperatures. As the oxidation temperature approaches 240°C, the critical volume fractions of the conductive adhesives are strongly affected by oxidation temperature and particle shape, owing to the formation of oxides such as Cu₂O on the surface of silver‐coated copper powder—Cu diffuses from the interior to the surface of silver‐coated copper powder and reacts with the oxygen in the air. Silver‐coated copper powder with flake‐shaped particles shows lower critical volume fractions in conductive adhesives than silver‐coated copper powder with spherically shaped particles. Polym. Eng. Sci. 44:2075–2082, 2004. © 2004 Society of Plastics Engineers.     

Preparation and reliability of wearable light-storing buttons

The potential for a large number of applications has stimulated the exploration of the preparation of wearable light-storing buttons. In this study, SrAl₂O₄：Eu²⁺, Dy³⁺ (SROED) was used as a long-lasting phosphorescent material, mixed with unsaturated polyester resin in proportion. A light-storing button with high stability and long afterglow time is obtained by the dispensing method. The surface and cross morphology, phase structure, photoluminescence spectrum, luminescence image, afterglow performance and mechanical hardness of the luminescent button are characterized. The results show that the luminescence performance of the phosphorescent button is significantly better than that of the original luminescent material SROED after high temperature and high humidity aging, xenon lamp aging, and thermal cycling aging test. Even in this study, the afterglow life of light-storing buttons can be maintained up to 7h. The luminescence mechanism of light-storing buttons is also discussed. This result will be very beneficial for the preparation of high-quality light-storing buttons. At the same time, it also expands the application of long afterglow materials in the field of smart wearables.     

Local charge regulation by doping Li+ in BaGa2O4:Bi3+ to generate multimode luminescence for advanced optical Morse code

In the field of advanced anti-counterfeiting research, it is a hot issue to develop a multimodal anti-counterfeiting material with adjustable luminescence characteristics. Here, persistent luminescent materials of BaGa₂O₄:xBi³⁺ (x = 0-0.02) and BaGa₂O₄:0.005Bi³⁺,yLi⁺ (y = 0.001–0.02) were synthesized by a solid state reaction at high temperature. BaGa₂O₄: Bi³⁺ exhibited a broad blue emission at ～470 nm (transition from [GaO₄]) and a sharp NIR emission at ～710 nm (³P₁→¹S₀ transition of Bi³⁺), upon UV excitation at 250 nm. Incorporation of Li⁺ in BGO: 0.005Bi³⁺ induced the emission color shifting from blue to green. After stoppage of UV excitation, the BGO:0.005Bi³⁺ exhibited white afterglow with emission peaks at the range of 500–700 nm. However, incorporation of Li⁺ leaded to a stronger green afterglow and a weaker NIR afterglow. When the afterglow disappeared, the sample outputted afterglow again after heating processing. The prepared samples exhibited time- and temperature-dependent multimode luminescence, so they were used as components, combined with Morse code to realize multi-modal dynamic anti-counterfeiting. The outcomes in this work indicate that the prepared luminescent materials have broad prospects in advanced anti-counterfeit applications.     

Toughening of PP/EPDM blend by compatibilization

To improve the mechanical properties of blends of polypropylene (PP) and terpolymer of ethylene–propylene–diene (EPDM), a triblock copolymer, (PP‐g‐MAH)‐co‐[PA‐6,6]‐co‐(EPDM‐g‐MAH), was synthesized by coupling reaction of maleic anhydride (MAH)‐grafted PP (PP‐g‐MAH), EPDM‐g‐MAH, and PA‐6,6. The newly prepared block copolymer brought about a physical interlocking between the blend components, and imparted a compatibilizing effect to the blends. Introducing the block copolymer to the blends up to 5 wt % lead to formation of a β‐form crystal. The wide‐angle X‐ray diffractograms measured in the region of 2θ between 10° and 50° ascertained that incorporating the block copolymer gave a new peak at 2θ = 15.8°. The new peak was assigned to the (300) plane spacings of the β‐hexagonal crystal structure. In addition, the block copolymer notably improved the low‐temperature impact property of the PP/EPDM blends. The optimum usage level of the compatibilizer proved to be 0.5 wt %. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1267–1274, 2000     

Low‐Temperature Sintering of β‐Spodumene Ceramics Using Li2O–GeO2 as a Sintering Additive

Low‐temperature sintering of β‐spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li₂O–GeO₂ sintering additive. Single‐phase β‐spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α‐alumina, and lithium carbonate powders mixture via the solid‐state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li₂O–GeO₂ additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10^?6 K^?1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt‐quenching routes. As a result, β‐spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li₂O–GeO₂ sintering additive via the conventional solid‐state reaction route. These results suggest that β‐spodumene ceramics sintered with Li₂O–GeO₂ sintering additive has a potential use as LTCC for multichip modules.     

Ag and Si Codoped Phosphate Glasses: Plasmonic Nanocomposites with Enhanced UV Transparency

The use of silicon powder to produce plasmonic Ag nanocomposite phosphate glasses which also exhibit improved transparency in the ultraviolet (UV) is proposed. Ag₂O/Si codoped glasses were prepared in a barium‐phosphate matrix by a simple melt‐quench method in ambient atmosphere. The as‐prepared glasses exhibit enhanced UV transparency, whereby the surface plasmon resonance of Ag nanoparticles (NPs) is manifested for the glasses with higher Ag₂O contents. ³¹P nuclear magnetic resonance spectroscopy is consistent with the formation of P–O–Si bonds, thus suggesting their possible role on the improved UV light transmission. Consequently, a model was presented accounting for the influence of silicon on the polymerization of the phosphate network concomitant with the creation of highly reactive oxygen species. Further exploiting the proposed reactive species, a real‐time spectroscopic study of the plasmonic response of Ag NPs in Ag/Si codoped glass samples was carried out during an in situ thermal processing. The temperature dependence of the Ag particle precipitation was studied in the 400°C–430°C range, from which an Arrhenius‐type plot allowed for estimating the activation energy of the process at 3.42 (±0.38) eV. Ultimately, the vanishing of the luminescence ascribed to Ag⁺ ions was observed in a heat‐treated sample, consistent with the high reactivity acquired by the glass matrix. Silicon thus appears promising for producing UV transparent glasses for high‐performance optics and for the reduction of Ag⁺ ions to produce Ag nanocomposites valuable for photonic (nanoplasmonic) applications.     

铝酸锶铕类长余辉荧光涂料的发光性能的研究

本文测定了两种长余辉荧光粉的吸收光谱和发射光谱。比较了其发光性能，并将其中性能较好的一种荧光粉加入常用的不饱和聚酯树脂和环氧树脂中，制得了可见光可激发的具有光致发光的性能的长余辉荧光涂料。研究了其光强衰减行为。讨论了荧光粉含量、涂层厚度与荧光光强、余辉时间等的关系     

Synthesis of ultra‐fine TaB2 nano powders by liquid phase method

Ultra‐fine TaB₂ powders were synthesized by a liquid phase method using tantalum ethoxide, boric acid and sucrose as the sources of tantalum, boron, and carbon. The TaB₂ precursor powders is a Ta–B–C–O network system, which were heat‐treated at lower temperature (1500°C) in normal argon atmosphere to obtain the TaB₂ powders. XRD confirms the presence of only hexagonal TaB₂, while EDS and XPS spectrums confirm the composition and element chemical states of TaB₂. The TEM images show a platelet shape of the TaB₂ powder and the monocrystal SAED pattern confirms the presence of hexagonal TaB₂. Particle size distribution curves show that particle size of the TaB₂ powders distributes in the range of 30‐160 nm, whose mean particle size is 106 nm.     

A building-block strategy for dynamic anti-counterfeiting by using (Ba,Sr)Ga2O4:Sm3+ new red persistent luminescent phosphor as an important component

Long persistent luminescence materials developed to commercial standards are primarily concentrated in the blue and green regions, with only a few in the red region. Red, as one of the three basic colors, can be mixed in various proportions with blue and green to yield various colors. The development of red persistent phosphors has a broader application potential but remains a challenge. A solid-state reaction method was used to synthesize new red persistent luminescent materials of Ba_1-xSr_xGa₂O₄:Sm³⁺ (x = 0–0.09). In BaGa₂O₄, both Sr²⁺ and Sm³⁺ preferentially occupy the Ba²⁺ site rather than the Ga³⁺ site. When exposed to UV light at 254 nm, the phosphors emit the characteristic red emission of Sm³⁺ at wavelengths ranging from 500 nm to 750 nm. After removing the UV light source, an intense red afterglow that lasted more than 1400 s was observed. The red afterglow signal reappears after a heating process. Doping Sr²⁺ reduces the trap depth and improves the red persistent luminescence significantly. Because the escaped electrons from traps compensate for the emission loss of Sm³⁺ during the heating process, the red phosphors have unimaginably luminescent thermal stability. Thus, the emission intensity at 200 ^°C is 1.6 times that at room temperature. The prepared red persistent phosphors show multimode luminescence, with the output signal being time and temperature sensitive, indicating that they are potential luminescent materials for anti-counterfeiting applications. Finally, a building-block strategy for advanced anti-counterfeiting applications of dynamic display information is proposed, with red persistent phosphors serving as an important component combined with upconversion phosphors of NaYF₄:Yb³⁺, Tm³⁺, and green persistent phosphors of SrAl₂O₄:Eu²⁺, Dy³⁺.     

Understanding the Role of Triblock Copolymers for the Synthesis of Mesoporous Alumina,and Its Adsorption Efficiency for Congo Red

Mesoporous alumina (MA)was synthesized by sol–gel based evaporation‐induced self‐assembly process using aluminum isopropoxide as alumina source in the presence of three different types of triblock copolymers (TBCs), F68, F127, and L64. The role of different TBCs as surfactants on thermal, crystallization, textural, and microstructural properties of the alumina powders was studied. To understand the effects of different copolymers, the adsorption efficiency of the samples for Congo red (CR) was studied. For all the surfactants, the XRD results showed the stability of γ‐Al₂O₃ phase up to 1000°C for 1 h dwell time. A maximum value (431.8 m²/g) of Brunauer–Emmet–Teller surface area was obtained for the 400°C‐treated powder prepared from F68 surfactant. The transmission electron microscopy micrograph exhibited worm‐like mesoporous structures of the 400°C‐treated powders prepared from F68 and F127 surfactants_. The adsorption performance for CR of the 400°C‐treated powders for different surfactants was in the order of F68 > F127 > L64. A tentative mechanism was illustrated to understand the roles of different block copolymers on the properties of the prepared MA.     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

Preparation of stable luminescent poly(methyl methacrylate)–europium complex nanospheres and application in the detection of hydrogen peroxide with the biocatalytic growth of gold nanoparticles

A simple and effective solvent swelling method was developed for the preparation of poly(methyl methacrylate) (PMMA)/europium (Eu) complex hybrid nanospheres. Transmission electron microscopy and dynamic light scattering results indicate that the as‐prepared PMMA–Eu nanoparticles had a spherical morphology, with a narrow particle size distribution ranging from 100–200 nm. The PMMA–Eu nanospheres exhibited strong red emissions with a maximum peak at 612 nm under UV excitation, and the luminescence lifetime of the Eu complex was enhanced after it was swollen into PMMA nanospheres. Furthermore, the luminescence intensity of the PMMA–Eu nanospheres was very stable in various severe media, including aqueous solutions with various pHs, 1 mM Ca²⁺, 1 mM Fe²⁺, 1 mM Cu²⁺, 0.1M phosphate‐buffered saline solution, 1 mM citric acid solution, 1 mM lysine, and 1 mM glutamic acid. After the nanospheres were incubated at various temperatures for 1 h, the luminescence properties remained stable when the temperature was less than 40°C yet decreased slightly between 40 and 60°C and decreased rapidly at higher temperatures. These luminescent nanospheres were successfully applied in the luminescence‐sensing assay of hydrogen peroxide and exhibited a high sensitivity and broad linear concentration range. Because of their unique luminescence properties, the as‐synthesized PMMA–Eu nanospheres are expected to have great potential for use as luminescent labels or probes for long‐time imaging and analysis in which severe media situations are present. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

An Upconversion Niobium Pentoxide Bulk Glass Codoped with Er3+/Yb3+ Fabricated by Aerodynamic Levitation Method

(82?x)NbO_2.5–17.4LaO_1.5–xZrO₂(NLZ) (x = 7.5, 10, 12.5, 15, 17.5, and 20) bulk glasses codoped with Er³⁺/Yb³⁺ were successfully fabricated by aerodynamic levitation method for the first time. The structure, thermal stability, and luminescent properties of the samples were investigated systemically by XRD, differential scanning calorimetry, and upconversion spectra. Under 980 nm laser excitation, all samples exhibited green and red upconversion emissions centered at 531, 546, and 674 nm. Results showed that the sample with 15 mol% ZrO₂ obtained the most efficient upconversion luminescence and good thermal stability with the glass‐transition temperature as high as 743 °C. The effect of the addition of ZrO₂ on the structure behavior and the phonon density in the glass was investigated by Raman spectra, which are the key factors for the upconversion luminescence intensity.     

Blends of polypropylene with solid silicone additive

Blends of polypropylene (PP) and silicone masterbatch (SMB_PP)—a commercial formulation consisting of an ultrahigh molecular weigh polydimethylsiloxane (PDMS) dispersed in PP—were prepared by melt mixing in an internal mixer. Four binary blends with different SMB_PP content and two ternary blends containing silane‐grafted polypropylenes (PP‐VTES) of different VTES content as compatibilizer were produced. The blends were analyzed by melting flow rate, rotational rheometry, scanning electron microscopy, and differential scanning calorimetry (DSC). In all blends, the SMB_PP remained as dispersed phase in the continuous PP matrix. The addition of PP‐VTES reduced significantly the size of the SMB_PP domains. Rheological and morphological data strongly indicate that the PP‐VTES acts only by lowering the interfacial tension of the system without generating strong interaction between SMB_PP domains and the PP matrix. The dimensions of the SMB_PP domains and the interfacial energy were observed to determine the characteristics of the pseudoplastic behavior of the blends in the melt state. For both binary and ternary blends, the SMB_PP domains showed nucleating effect leading to an increase of the degree of crystallinity. However, the decrease in the interfacial energy and viscosity promoted by the addition of PP‐VTES to the system led to a more intense nucleating effect and to an increase of crystallization, melting temperatures, and melting enthalpy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 226–233, 2007     

Direct Formation of Luminescent Fine Crystals Based on (Y,Eu)TiNbO6 Complete Solid Solution with High Crystallinity

Luminescent fine crystals of Y_1.00?xEu_xTiNbO₆, x = 0–1.00 with high crystallinity were directly synthesized by mild hydrothermal method from weakly basic precursor solution mixtures of YCl₃, EuCl₃, TiOSO₄, and NbCl₅. Orthorhombic aeschynite‐type crystals in the range of 0.5–2.0 μm consisting of crystallites with 33–91 nm based on a complete solid solution in the YTiNbO₆–EuTiNbO₆ system were hydrothermally formed at 240°C for 5 h. A single phase of as‐prepared aeschynite‐type structure was maintained in all the (Y,Eu)TiNbO₆ solid solution after heating at temperatures up to 1000°C for 1 h in air. In the range of composition x ≤ 0.6, the as‐prepared aeschynite‐type (Y,Eu)TiNbO₆ solid solutions transformed to a single phase of euxenite structure after heat treatment at temperatures higher than 1100°C–1200°C. The as‐prepared (Y,Eu)TiNbO₆ fine crystals in the range of composition x = 0.75–0.90 showed the strongest luminescence in the red spectral region: strong red (⁵D₀→⁷F₂ transition of Eu³⁺) and weak orange light (⁵D₀→⁷F₁) line spectra among the as‐prepared and heat‐treated samples. Another wet chemical synthesis route confirmed the advantage in directly synthesizing the (Y,Eu)TiNbO₆ crystals through this hydrothermal method because heating at 1200°C for 1 h in air was necessary for obtaining crystalline (Y,Eu)TiNbO₆ with sufficient luminescence intensity in a composition Y_0.70Eu_0.30TiNbO₆ from amorphous powders that were formed via co‐precipitation method.