NUV-pumped luminescence of thermally stable samarium-activated alkali metal borophosphate phosphor

Exploring outstanding rare-earth activated inorganic phosphors with good thermostability has always been a research focus for high-power white light-emitting diodes (LEDs). In this study, we report a Sm3+-activated KNa4B2P3O13 (KNBP) powder phase. Its particle morphology, photoluminescence properties, concentration quenching mechanism, thermal quenching mechanism, and chromatic properties are demonstrated. Upon the near-ultraviolet (NUV) irradiation of 402 nm, the powder phase exhibits orange-red visible luminescence performance, originating from typical 4G5/2→6HJ/2 (J = 5, 7, 9) transitions of Sm3+. Importantly, the photoluminescence performance has good thermostability, low correlated color temperature (CCT), and high color purity (CP), indicating its promising application in the NUV-pumped warm white LEDs.

Bayesian approach to powder phase identification

Identification of unknown materials using X-ray powder diffraction patterns is a commonly used and well established technique with a number of proved implementations. Generally, qualitative phase analysis of X-ray diffraction data includes ranking of candidate phases on the basis of similarity of their diffraction patterns to the measured one. A standard strategy of such a ranking by algorithmization of manual search criteria may become inconvenient for modification and adaptation for problems that are not supported by our intuition. Here, the problem of providing physically grounded expressions for candidate phase ranking is addressed. The approach is based on calculation of Bayesian posterior probabilities of the phases' presence in the sample. The choice of the expressions for the prior probabilities for deviations of phases' diffraction patterns from database entries determines the degree of physical detailing and may be made according to the specifics of the problem being solved. It is shown that even for simple exponential expressions for prior probabilities the approach identifies the phases for IUCr round robin cases correctly, as well as ensuring sufficient robustness of the results with respect to diffraction peak shifts and intensity variations.

On the Preparation and Properties of Luminous Concrete

The luminous concrete was made by doping phosphors into the raw concrete materials. The CaO (xDy3+, yNa+ series) phosphors were compounded by high temperature solid state method. Florescent powder phase, excitation and emission spectra were analyzed. The results show that the peak of florescent powder emission spectrum locates at 480nm or so, corresponds the transition 4F9 /26H15 /2 of Dy3+. There are a series of lines in the range of 240-420nm by monitoring the excitation spectrum of 480nm emission. Strong excitation peaks are at 360nm and 375nm. Influences of doped phosphors on concrete mechanical properties were studied. The results show that with the growth of phosphor dosage, concrete compressive strength and flexural strength decrease. SEM images show that the fluorescent powder particle is approximately spherical, and uniformly mixed in concrete.

Bovine Bone Processing for Biofilter Application

This work involves the processing of bovine bone for use as biofilter collector of heavy metals in water. Before processing, it was necessary to clean the bone selected for removing the organic material adhered thereto. Drying was done in weathered during 18 days. Then the bones were calcined at a constant temperature of 750°C for 6 hour. The bone grinding was performed by means of an analytical mill in order to obtain a finer grain size. Once processed, the bovine bone powder was characterized by X-ray diffraction and fluorescence analyses. The results showed that the powder phase is less crystalline hydroxyapatite, when compared to highly crystalline synthetic hydroxyapatite, which favors the sorption capacity of lead by bovine bone.

Fabrication of Bi0.5Na0.5ZrO3 Powder by Mixed Oxide Method

Lead-free bismuth sodium zirconate powder with formula Na0.5Bi0.5ZrO3 was prepared by conventional mixed oxide method. Bismuth sodium zirconate (BNZ) powder with 10wt%Na2CO3 was calcined at 800 °C for 2 h dwell time. Investigation of the effects of re-calcination and dwell time on phase formation of powders was also carried out. The results revealed that re-calcination significantly affected the formation of single-phase BNZ powder. Phase characteristics were checked by X-ray diffraction (XRD). Powder Cell software was employed to simulate crystal structure of BNZ powder. It was found that BNZ powder most likely possessed an orthorhombic structure. SEM result showed its average particle size was 0.47 mm and composition measured EDX correlated with theoretical composition of BNZ.

X Ray Topography Study of Deformed Crystal-Quasicrystal Composites of Al Cu Fe Alloy

Crystal-quasicrystal columnar composites (CQ composites) of Al Cu Fe alloy subject to tensile strain at room temperature were studied by the reflective X ray topography. In those composites singlecrystalline β phase occurred as the matrix and rods consisting of quasicrystalline ψ phase and crystalline λ phase as the reinforcement. X-ray topograms of plate like composite specimens were obtained using reflexes of singlecrystalline matrix. It has been found that at strains ε up to 0.33% in a linear range of stress strain σ(ε) relationship the topograms remain unchanged. Instead, at ε higher than 0.33% significant contract changes have been observed in some areas of topograms. It has been determined that at ε higher than 0.33% the components of misorientation angle of those areas increase with increasing strain. Methods of powder phase analysis, metallographic examinations by means of optical microscopy methods and X-ray diffraction topography methods were used.

Structural Characterization and Ionic Conductivity of Metastable Gd2(Ti0.65Zr0.35)2O7 Powders Prepared by Mechanical Milling

We analyze in this work the influence of ordering on the oxygen ion dynamics in the ionic conductor Gd2(Ti0.65Zr0.35)2O7, prepared by mechanical milling. As-prepared powder phase presents a metastable anion deficient fluorite-type of structure below 800°C becoming a disordered pyrochlore above this temperature. Such phase transformation implies a significant increase in the ionic conductivity of this material as a result of a systematic decrease in the activation energy for the dc conductivity, from 1.23 to 0.78 eV. Electrical conductivity relaxation is well described by the Kohlrausch-Williams-Watts (KWW) stretched exponential function with the fractional exponent n decreasing systematically with increasing sintering temperature (increasing ordering) as a result of decreasing ion-ion interactions in better ordered samples.