Preparation and luminescent properties of GdOF:Ce,Tb nanoparticles and their transparent PMMA nanocomposites

GdOF:Ce, Tb nanoparticles and their poly (methyl methacrylate) (PMMA) nanocomposites have been successfully prepared by a thermolysis route and thermal polymerization of methyl methacrylate (MMA) monomer, respectively. The obtained nanoparticles and nanocomposites are characterized by XRD, EDS, TEM, FTIR, TGA, UV–Vis and PL spectrum. The as-synthesized transparent GdOF:Ce, Tb/PMMA nanocomposites exhibit green photoluminescence under the irradiation of 254 nm UV lamp due to the incorporation of luminescent GdOF:Ce, Tb nanoparticles into the PMMA matrix. The present route would provide a general strategy to prepare other functional nanocomposites.     

Preparation and optical properties of sol–gel derived photo-patternable organic–inorganic hybrid films for optical waveguide applications

Photo-patternable TiO₂/organically modified silane hybrid films were prepared by combining a low-temperature sol–gel technique with a spinning–coating process. A ridge waveguide pattern was fabricated by ultraviolet light irradiation through a mask placed contact with the hybrid film in direct. Optical properties and photochemical activity of the hybrid film, including refractive index, thickness, propagation mode, and propagation loss, were studied and monitored by a prism coupling technique and Fourier transform infrared spectroscopy. The change of transmittance with exposure time was also observed by ultraviolet–visible spectroscopy. These results indicate that the hybrid film is potential application for fabrication of photonic devices by ultraviolet light irradiation. The structure of ridge waveguide pattern was characterized and studied by scanning electron microscope and surface profiler. The fabrication process of the as-prepared photosensitive hybrid film as compared with traditional binary mask has a great amount of advantages of cost-effective, simple, and smooth surface over non-photosensitive material methods.     

Crystallization and oxidation resistance properties of boron modified silicon oxycarbides derived from polymeric precursors by sol–gel method

Boron modified silicon oxycarbides (SiBOCs) were prepared from sol–gel derived pre-ceramic polymeric gels followed by pyrolysis at 950 °C under nitrogen. As-prepared SiBOC was found to be amorphous in nature and partially crystallized to SiO₂ at 1500 °C. The effect of boron incorporation on the crystallization of SiBOC was studied and the result revealed that the tendency to crystallization decreased with increasing boron content. This is due to the formation of Si–O–B bridges at higher temperatures, which retards the crystallization of SiO₂, evidenced from FTIR studies. SiBOC also exhibited excellent oxidation resistance ability at high temperature.     

Photoluminescence and energy transfer investigation from SiO2: Tb,Au inverse opals to rhodamine-B dyes

Energy transfer has attracted extensive attention due to its widespread applications in medical diagnostics, DNA analysis and lighting devices. There are few reports on the energy transfer from rare earth ions to dyes. In the present work, the SiO₂:Tb inverse opals with and without Au nanoparticles were prepared, and the organic rhodamine-B (RhB) dyes were filled into the voids of SiO₂:Tb inverse opals. Non-radiative and radiative energy transfer processes from the SiO₂:Tb inverse opals to the RhB were observed. The influence of Au nanoparticles and photonic band gap on the energy transfer from SiO₂:Tb inverse opals to the RhB was investigated. The Au nanoparticles enhanced energy transfer was observed due to the surface plasmon resonance effects of the Au nanoparticles. When the emission peaks from the SiO₂:Tb inverse opal is overlapped with the photonic band gap, the emission suppression of the SiO₂:Tb inverse opal as well the emission enhancement of the RhB dyes were obtained, which is attributed to improved energy transfer caused by the photonic band gap. The steady state rate equations were used to explain enhancement of energy transfer caused by the photonic band gap.     

Preparation and conductivity of solid high-proton conductor silica gel containing 80 wt.% decatungstodivanadogermanic acid

The silica gel containing decatungstodivanadogermanic heteropoly acid was prepared by means of the sol-gel method. Infrared spectrum and XRD pattern revealed that the Keggin structure characteristic of GeW₁₀V₂O₄₀⁶⁻ anion was present in the silica gel skeleton. The regularity of the change of the characteristic peaks in the infrared spectrum was investigated. The silica gel exhibited considerably high-proton conductivity. The proton conductivity of the gel containing 80 wt.% decatungstodivanadogermanic acid is 5.37 × 10^− 2 S cm^− 1 at room temperature (18 °C).     

Photoluminescence characteristics of Ti2S3 nanoparticles embedded in sol–gel derived silica xerogel

Ti₂S₃ nanocrystallites embedded in sol–gel derived silica xerogel have been prepared. Their photoluminescence (PL) characteristics have been evaluated and compared with those of pure silica xerogel. UV–vis absorption spectra, transmission electron micrograph, excitation spectra and PL spectra of the doped and undoped samples have all been investigated. Two emission peaks have been observed from the doped samples, one at 440 nm (λ_ex=380 nm) while the other at 600 nm (λ_ex=550 nm). The latter has been assigned to the Ti₂S₃ nanocrystallites in the silica xerogel. Therefore, a novel luminescence property can be observed by introducing the semiconductor nanoparticles into the silica xerogel.     

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

Mechanical properties and thermal stability of nitrogen incorporated diamond-like carbon films

The nitrogen incorporated diamond-like carbon films were deposited on Si (100) substrates by arc ion plating (AIP) under different N₂ content in the gas mixture of Ar and N₂. The influence of N₂ content on the film microstructure and mechanical properties was studied by atomic force microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nanoindentation. It was found that the hardness (H), elastic modulus (E), elastic recovery (R) and plastic resistance parameter (H/E) decrease with increasing the nitrogen content. The decrease of mechanical properties of DLC films resulted from nitrogen incorporation was associated with total sp³ carbon bond content and N-sp³C bond content. The structural modification as well as mechanical properties of the annealed nitrogen incorporated diamond-like carbon films was investigated as a function of annealing temperature. Raman spectra indicate that the I_D/I_G ratio starts to increase and G peak position shifts upward at the annealing temperature over 500 °C. The hardness and elastic modulus of thermally annealed nitrogen incorporated DLC films decreased slightly at lower annealing temperature and then significantly decreased at higher annealing temperature. The strong covalent bonding between C and N atoms is expected to be effective on their thermal stability enhancement.     

Stored energy, vacancies and thermal stability of ultra-fine grained copper

The stored energy and thermal stability of oxygen-free high conductivity copper processed by equal channel angular pressing up to 16 passes at room temperature was studied by differential scanning calorimetry. Stored energy increased with strain up to four passes, after which it saturated at 0.95 ± 0.05 J/g. This saturation value is 20% higher than from conventional cold rolling. The microstructure of the copper after eight passes was characterized by an average subgrain size of about 0.21 μm and high-angle boundary fraction of about 35%. The contributions to the stored energy from defects were calculated and compared, suggesting that the stored energy mainly originates from boundaries and vacancies. The restoration activation energy after eight passes was between 77 and 80 kJ/mol. The higher stored energy and lower activation energy compared to cold-rolled copper is attributed to excess vacancies.     

Co-existence phenomenon of Ce3+/Ce4+ and Tb3+ in Ce/Tb co-doped Zn2(BO3)(OH)0.75F0.25 phosphor: Luminescence and energy transfer

A serials of Zn₂(BO₃)(OH)_0.75F_0.25 (ZBF), Tb³⁺, Ce^3+/4+ single-doped ZBF and Tb³⁺/Ce^3+/4+ co-doped ZBF novel phosphors with belt-like morphology were obtained through hydrothermal reaction without any surfactant. The obtained samples were characterized by XRD, SEM, EDS, TEM, TGA, XPS, DR, PL, and DT. The TGA curve shows that the phosphor is thermal stability. XPS results show that Tb³⁺ is present in the Tb-doped phosphor, and the Ce³⁺/Ce⁴⁺ mixed valence is present in the Ce-doped phosphor. The PL results indicate that ZBF host material and ZBH:Ce^3+/4+ can emit blue light, ZBF:Tb³⁺ can emit green light. Compared with the Tb³⁺ single doped phosphor, the Tb³⁺/Ce^3+/4+ co-doped phosphors shown stronger emission and shorter decay time, which is attributed to the effective energy transfer from the Ce^3+/4+ to Tb³⁺ ions.     

Photoluminescence of TiO2 films co-doped with Tb/ Gdand energy transfer from TiO2/Gd to Tb ions

Nanometer TiO₂ thin films doped with different concentration of Tb were prepared by sol-gel method and characterized by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. XRD results show preferentially oriented (101) anatase films. TEM image indicates that the TiO₂ films consist of TiO₂ grains with diameter about 15 nm. Under room temperature, strong visible luminescence of Tb³⁺ ions due to intra-4f shell transitions are obtained and the PL intensity is found to have a well matching relation with the doping concentration of Tb³⁺ ions. Concentration quenching of PL occurs when Tb³⁺ concentration exceeds a certain value (9.2 mol%). Furthermore, the luminescence intensity is improved obviously after co-doping with Gd³⁺ ions because of the sensitization effects of Gd³⁺ ions to Tb³⁺ ions in TiO₂ system. The energy transfer mechanism from TiO₂ and Gd³⁺ ions to Tb³⁺ ions was proposed.     

Ce to Tb energy transfer in alkaline earth (Ba, Sr or Ca) sulphate phosphors

Energy transfer between Ce³⁺ and Tb³⁺ dopants in alkaline earth (Ba, Sr or Ca) sulphate phosphors is investigated. Among these three phosphors, CaSO₄:Ce³⁺,Tb³⁺ showed maximum Tb³⁺ green emission on excitation with UV light. Photoluminescence measurements reveal that the emission intensity from CaSO₄:Ce³⁺,Tb³⁺ is comparable with that of the commercial green lamp phosphor Ce_0.65Tb_0.35MgAl₁₁O₁₉. Optimum concentrations of dopants in CaSO₄:Ce³⁺,Tb³⁺ are 0.2 mol% each and the optimum sintering treatment following re-crystallisation is 600 °C for 1 h duration. The effect of charge compensator in all the three phosphors is also studied.     

Tensile properties and thermal stability of ZnO-coated aluminum borate whiskers reinforced 2024Al composite

ZnO-coated aluminum borate whiskers reinforced 2024Al composite was fabricated by squeeze casting. Interfacial microstructures and tensile properties of the composite in as-cast and after thermal exposure were investigated. Fracture mechanisms of the composite in as-cast and after thermal exposure were also investigated. The results show that ZnO coating of the whiskers reacts with molten 2024Al and MgAl₂O₄ forms at the interface during squeeze casting. On the one hand, the interfacial reaction between ZnO and 2024Al can improve the wettability of the whiskers by molten 2024Al, increasing the tensile properties of as-cast composite. On the other hand, during thermal exposure, MgAl₂O₄ at the interface can effectively hinder serious interfacial reactions between the whiskers and magnesium in the matrix of 2024Al, improving the thermal stability of the composite at high temperatures.     

Structure,optical properties and thermal stability of Al2O3-WC nanocomposite ceramic spectrally selective solar absorbers

Traditional metal-dielectric composite coating has found important application in spectrally selective solar absorbers. However, fine metal particles can easily diffuse, congregate, or be oxidized at high temperature, which causes deterioration in the optical properties. In this work, we report a new spectrally selective solar absorber coating, composed of low Al₂O₃ ceramic volume fraction (Al₂O₃(L)-WC) layer, high Al₂O₃ ceramic volume fraction (Al₂O₃(H)-WC layer) and Al₂O₃ antireflection layer. The features of our work are: 1) compared with the metal-dielectric composites concept, Al₂O₃-WC nanocomposite ceramic successfully achieves the all-ceramic concept, which exhibits a high solar absorptance of 0.94 and a low thermal emittance of 0.08, 2) Al₂O₃ and WC act as filler material and host material, respectively, which are different from traditional concept, 3) Al₂O₃-WC nanocomposite ceramic solar absorber coating exhibits good thermal stability at 600 °C. In addition, the solar absorber coating is successfully modelled by a commercial optical simulation programme, the result of which agrees with the experimental results.     

Gd3+-Tb3+能量转移与Tb3+自敏化效应对重金属锗酸盐玻璃发光性能的影响

研究了一组Tb^3 掺杂重金属锗酸盐玻璃的发光特性。玻璃样品的X射线激发发射光谱结果显示,玻璃基质中由Gd^3 离子向发光中心Tb^3 的能量转移机制以及在一定浓度范围内Tb^3 之间的交叉弛豫过程对玻璃的发光性能有重要影响。前者表现在Gd^3 紫外发射光的减弱及Tb^3 绿发射光的增强,后者则显示Tb^3 在一定浓度范围内所特有的自敏化效应,使其蓝发射光减弱、绿发射光增强。第3种稀土离子La^3 的引入对发光中心Tb^3 离子具有分离效应,使Tb^3 之间的交叉弛豫概率降低,蓝发射光增强。     

Effect of nitrogen addition on the properties and thermal stability of fluorinated amorphous carbon films

Continuous fluorinated amorphous carbon (a-C : F) films doped with nitrogen (a-C : F : N) were deposited by plasma enhanced chemical vapor deposition using CF₄ and C₂H₂ gases as precursors with the addition of N₂ gas. The surface morphologies, chemical compositions, deposition rates, thermal stability and mechanical properties of these films varied with the deposition parameters, including CF₄ and N₂ feed gas concentrations, processing pressure, plasma power and substrate temperature. With increasing N₂ feed gas concentration, the nitrogen content of the a-C : F : N films increased to about 6 at.% and contributed to higher mechanical properties. After thermal annealing, the a-C : F films with higher fluorine contents exhibited more obvious fluorine release and extensive film thickness shrinkage, whereas the a-C : F : N films with higher contents of nitrogen doping yielded less composition variations, smaller thickness shrinkages, higher mechanical properties, and conclusively better thermal stability.     

Thermal stability and mechanical properties of nanostructured Ti–24Nb–4Zr–7.9Sn alloy

Thermal stability of the nanostructured grains of cold-rolled Ti–24Nb–4Zr–7.9Sn alloy and corresponding variations in mechanical properties were investigated. The activation energy for grain growth was found distinct below and above the ( + β)/β transus of 950 K, with values of 47 and 206 kJ/mol, respectively. Due to the pinning effect of the precipitates at β grain boundaries, grains sizes can be maintained at less than 100 nm during prolonged annealing at temperatures up to 773 K, and are less than 1 μm for annealing temperature up to 923 K and time up to 2 h. Annealing above the β transus resulted in coarse grains with sizes of tens of micrometers in less than 2 h. Tensile and hardness tests showed rapid strengthening with the increase of annealing time below 773 K, which was attributed to both the rapid formation of nano-sized precipitates and the slow growth rate of β grains. By adjusting the grain size of the cold-rolled material the high strength/low Young's modulus match desirable for implant applications can be improved over the hot-rolled bars with coarse grains.     

Surface morphologies and properties of pure and antimony-doped tin oxide films derived by sol–gel dip-coating processing

A simple laboratory technique for the routine preparation of antimony-doped tin oxide (ATO) on float glass substrates (25 mm × 76 mm × 1 mm) was described. As-prepared thin films were dried at temperature of 100 ± 5 °C and annealed at temperatures of 400–550 °C. Microstructural and morphological analyses of as-prepared films were performed at different conditions. The evolution of grain size and the morphologies of ATO films were analyzed by means of atom force microscopy (AFM) and digital microscope. The studies suggested that higher Sb-doped level and higher annealing temperature led to a decrease in the surface roughness of the deposited films. The XRD patterns revealed that as-prepared ATO films were in the crystallization of a tetragonal rutile structure of SnO₂ with highly (1 1 0) preferred orientation. Their optical properties were analyzed by U-3310 spectrophotometer. The transmission of the ATO thin films was obtained as high as 80–90% in visible region, but decreased substantially in IR region. The sheet resistance of the investigated thin films was determined by four-probe method, showing that it was about 85–100 Ω □⁻¹which decreased with the increase of antimony-doped concentration.     

Luminescent properties and energy transfer processes of co-doped Yb–Er poly-crystalline YAG matrix

A poly-crystalline YAG matrix was obtained through the precipitation method; this matrix was single and co-doped with ytterbium and erbium ions, i.e., Yb:YAG, Er:YAG and Yb,Er:YAG. It is found that the measured luminescent properties are similar to those reported for a mono-crystal YAG matrix. In addition, by studying the energy transfer processes in co-doped samples, it is shown that at high erbium concentrations the red emission is enhanced through an up-conversion process that takes place from the ⁴I_13/2 to the ⁴F_9/2 state of erbium ions. This enhanced red emission becomes comparable in intensity to the observed green emission and occurs by pumping at 800 nm through a back energy transfer process.     

Preparation,characterization and thermal stability of bentonite modified with bis-imidazolium salts

Sodium bentonite was modified with several organic bis-imidazolium salts. Organoclays with water soluble surfactants were prepared by the traditional cation exchange reaction. The bis-imidazolium-bentonites were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (PXRD) and thermogravimetric analysis (TGA). The effect of chemical composition and molecular weight of the salts on the thermal stability and basal spacing were evaluated. The bis-imidazolium-bentonites showed enhanced thermal stability (300–400 °C) and may be potentially useful materials for melt processing of polymer/layered silicates nanocomposites.