Silicon-based oxynitride and nitride phosphors for white LEDs—A review

As a novel class of inorganic phosphors, oxynitride and nitride luminescent materials have received considerable attention because of their potential applications in solid-state lightings and displays. In this review we focus on recent developments in the preparation, crystal structure, luminescence and applications of silicon-based oxynitride and nitride phosphors for white light-emitting diodes (LEDs). The structures of silicon-based oxynitrides and nitrides (i.e., nitridosilicates, nitridoaluminosilicates, oxonitridosilicates, oxonitridoaluminosilicates, and sialons) are generally built up of networks of crosslinking SiN₄ tetrahedra. This is anticipated to significantly lower the excited state of the 5d electrons of doped rare-earth elements due to large crystal-field splitting and a strong nephelauxetic effect. This enables the silicon-based oxynitride and nitride phosphors to have a broad excitation band extending from the ultraviolet to visible-light range, and thus strongly absorb blue-to-green light. The structural versatility of oxynitride and nitride phosphors makes it possible to attain all the emission colors of blue, green, yellow, and red; thus, they are suitable for use in white LEDs. This novel class of phosphors has demonstrated its superior suitability for use in white LEDs and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable correlated color temperatures (CCTs), and brilliant color-rendering properties.     

Biocompatible fluorescence-enhanced ZrO₂-CdTe quantum dot nanocomposite for in vitro cell imaging

With advances of quantum dots (QDs) in bioimaging applications, various materials have been used to coat QDs to reduce their nanotoxicity; however, the coating could introduce new toxic sources and quench the fluorescence in bioimaging applications. In this work, ZrO?, an excellent ceramic material with low extinction coefficient and good biocompatibility, is utilized to coat CdTe QDs for the first time. Experimental results show that ZrO?-QD nanocomposites with the size of ~30 nm possess enhanced fluorescence emission, lower nanotoxicity and gradually increased fluorescence under 350 nm light illumination. After functionalization with folic acid, they were applied to label cultured HeLa cells effectively. Therefore, the ZrO?-QD nanocomposites could be promising biocompatible nanomaterials with strong fluorescence emission to replace or complement QDs in biomedical applications.     

Fine yellow α-SiAlON:Eu phosphors for white LEDs prepared by the gas-reduction–nitridation method

Yellow-emitting a-SiAlON:Eu²⁺ phosphors were synthesized by the gas reduction and nitridation of a homogeneous oxide precursor in a CaO–Al₂O₃–SiO₂–Eu₂O₃ system at 1400–1450 °C using an NH₃–CH₄ mixture gas as a reduction–nitridation agent. The precursor was prepared by a sol–gel process using a low-cost nitrate, tetraethyl orthosilicate and citric acid as the starting materials. The effects of reaction parameters such as heating rate, temperature, holding time and CH₄ content on the composition, microstructure and photoluminescence of the prepared powders were investigated. Nearly single-phase α-SiAlON was successfully synthesized by the one-step gas reduction and nitridation without the need for post-annealing at a higher temperature. The prepared powders consisted of relatively well-dispersed and uniform crystals with a hexagonal shape. The photoluminescence spectra of Eu-doped Ca-α-SiAlON phosphors excited by near-ultraviolet or blue light showed a broad, yellow emission band at 500–700 nm, which agrees well with that obtained from phosphors prepared by the conventional solid-state reaction.     

Ce-doped Al2O3−YAG eutectic and its application for white LEDs

Ce-doped Al₂O₃−YAG (Y₃Al₅O₁₂, yttrium aluminum garnet) eutectic, a resin-free phosphor for white light emitting diodes (WLEDs), was successfully grown by the Czochralski method. X-ray diffraction and scanning electron microscopy show that this material has a typical eutectic structure of interpenetrating sapphire and garnet phases, as well as lamellar spacing in the order of tens of microns. The eutectic has a higher Ce³⁺ segregation coefficient than YAG single crystal. The photoluminescence properties of this eutectic were also investigated. Results show that it is characterized by a wide excitation band, and that the luminous efficiency of a eutectic-packaged LED is higher than that of a phosphor powder-packaged LED. The findings indicate that the Al₂O₃−YAG eutectic is a promising phosphor for WLED applications.     

Synthesis of new green-emitting KBa1−xScSi3O9:Eu2+x phosphors for white LEDs

New green-emitting KBa_1−xScSi₃O₉:Eu²⁺_x phosphors for white LEDs were synthesized by a conventional solid-state reaction method. The obtained KBa_1−xScSi₃O₉:Eu²⁺_x phosphors show the strong broad optical absorption band from UV to blue light region and exhibit broad green emission with a peak at 521 nm under excitation at 405 nm due to the allowed 4f⁶5d¹−4f⁷ transition of Eu²⁺. Optimization of Eu²⁺ concentration resulted in the highest green emission peak intensity was obtained at the composition of KBa_0.94ScSi₃O₉:Eu²⁺_0.06, and the relative emission intensity of this phosphor was 32% of that of a commercial YAG:Ce³⁺ phosphor.     

Improvement of a Real Gas-Sensor for the Origin of Methane Selectivity Degradation by µ-XAFS Investigation

Nano-Micro Letters - We have directly investigated the chemical state of the Pd species in a real μ-gas sensor device by examining the μ-fluorescence X-ray absorption fine structure. The...     

Improvement of measurement accuracy in shadow moiré by considering the influence of harmonics in the moiré profile

A method for high-resolution three-dimensional shape measurement for a shadow moiré system is proposed. To increase the resolving power of the method, the problem caused by the harmonics of the moiré profile needs to be solved. It is well known that moiré fringes in a shadow moiré system have a nonsinusoidal profile caused by harmonics. The influence of the harmonics in moiré profile on the measurement accuracy of the method is discussed. The method is improved to eliminate the error caused by the harmonics in the moiré profile. Both simulation and experimental results show that the improved method can effectively reduce the influence of harmonics.     

Preparation and photoluminescence properties of γ-KCaPO4: Eu phosphors for near UV-based white LEDs

Novel whitish-blue phosphors based on a phosphate host matrix, γ-KCaPO₄: Eu²⁺, were prepared by a conventional solid-state reaction method using slightly phosphorus deficient conditions and their photoluminescence properties were investigated. The concentration quenching process, temperature dependence of the luminescence and decay curve were also investigated. The γ-KCaPO₄: Eu²⁺ phosphor was efficiently excited by UV-Visible light at wavelengths of 200-450 nm and exhibited a bright whitish-blue emission with a maximum peak wavelength of 473 nm. All of these characteristics suggest that the γ-KCaPO₄: Eu²⁺ phosphors combined with red phosphors could be applicable to near UV-based white LEDs, i.e., only two kinds of phosphor powders are needed for the formation of white light.     

Improvement of Content Uniformity of d-α-Tocopheryl Acetate as an Oily Drug in Granules by Emulsification

ABSTRACT

To elucidate the effects of an oily drug emulsification on its content uniformity in granules obtained by wet granulation with a high-shear mixer, d-α-tocopheryl acetate (VE) was emulsified with hydroxypropylcellulose (HPC-L) solution (mean diameter of the VE droplets was 1.3 μm). When VE was added to the mixing powder as the emulsion, nuclei rich in VE were not formed and then the content of VE was fairly uniform throughout the granules even at 2 min granulation. We found that the oily drug poor content uniformity could be improved significantly by adding an emulsified drug to the powder in granulation process.     

Testing the proficiency of analytical laboratories by means of inter-laboratory comparison tests – an important element in assurance of the uniformity of measurements

The role of proficiency testing of laboratories through inter-laboratory comparison tests in an effort to assure the uniformity of measurements is considered.     

Synthesis and field emission properties of topological insulator Bi₂Se₃ nanoflake arrays

High quality Bi(2)Se(3) nanoflake arrays with a large area and high-yield production have been fabricated by chemical vapor deposition. As the essential candidate for a topological insulator, the unique surface electronic states are considered to play a crucial role distinct from the bulk. Our experimental results show that environmental doping significantly affects the field emission properties of the synthesized Bi(2)Se(3) nanoflake arrays. X-ray photoelectron spectroscopy characterizations indicate that the rapid surface oxidation may prohibit the detection of the topological surface state and results in a low field emission current. This work provides another insight to investigate the surface state of topological insulator materials.     

Strength Improvement of CVD SiC Fibers by Electrochemical Surface Treatment

An electrochemical sudece-treatment method has been used for modifying surface condition of large diameter CVD SiC (W core) fibers. The average tensile strength of the fibers was increased obviously from 2270.1 to 3002.9 MPa. X-ray photoelectron spectroscopy (XPS) studies on the treated fiber sudece indicate that a silicon-oxide film (primarily α-SiO2) has formed,accompanying the precipitation of amorphous carbon as the products of an anode oxidation reaction. In addition, the substantial increase of fiber strength through the electrochemical treatment may be described to the formation of oxide films and elimination of defects on the fiber surface.     

Improvement of the critical current density in Bi-2223 ceramics by sodium–silver co-doping

Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_4?xNa_xO_y (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, dc electrical resistivity and magnetic-hysteresis loop measurements. It has been shown that the Na doping in low contents significantly improves the physical properties of Bi-2223 phase. Magnetic hysteresis measurements have shown that the largest hysteresis curve belongs to Bi_1.46Pb_0.36Ag_0.18Sr₂Ca₃Cu_3.95Na_0.05O_y sample including x = 0.05 Na content, indicating that it has best flux pinning capability in samples produced in this work. In addition, J_c values of the samples were calculated from the hysteresis loop measurement by using the Bean’s model showing that J_c increases with small amounts of sodium–silver co-doping.     

Environment-friendly biomimetic synthesis of TiO₂ nanomaterials for photocatalytic application

We have demonstrated an environment-friendly biomimetic synthesis method for the preparation of TiO(2) nanomaterials with different crystal phases and morphologies. This is the first time that it has been found that the crystal phase of TiO(2) can be controlled just by using different biotemplates, and cannot be changed by calcination up to 750?°C. In our experiment, anatase TiO(2) was obtained by using yeast and albumen templates, while rutile TiO(2) was formed by using dandelion pollen as the template.     

Improvement of mechanical properties of chromium–nickel sintered compacts by multiple rolling

The present paper provides details on the thermomechanical treatment of chromium–nickel alloys with high content of chromium, which leads to considerable improvement of their mechanical properties. The investigated alloys were prepared from Cr–Ni powder mixtures containing 50% and 80% of chromium in mass. They were formed by a particular sequence of cold and hot isostatic pressing. The as-sintered compacts were essentially brittle at room temperature, while they have exhibited considerable ductility after the special thermomechanical treatments. The treatment consisted of a sequence of repeated rolling and annealing operations, which is relatively simple and applicable in the industrial production. It is found that the treatments led to a more homogeneous, better alloyed structure and enhanced interdiffusion of the component metals.     

Improvement of thermal conductivity in 2D carbon–carbon composites by doping with TiC nanoparticles

Titanium-doped CC composites were prepared by liquid impregnation of a 2D carbon fibre preform using a mesophase pitch doped with TiC nanoparticles as matrix precursor. The effect of the addition of titanium carbide on the microstructure and thermal properties of CC composites is investigated. A higher degree of order was developed in the matrix of the Ti-doped composite which is the result of the catalytic graphitisation of carbon promoted by titanium. As a consequence, the thermal conductivity is higher in this doped material, despite the low dopant content introduced in the matrix, which points out the relevant contribution of the matrix to the thermal properties of the whole composite.