Structural strain in pyrites evaluated by X-ray powder diffraction

Two parameters for measuring the structural strain, the effective Debye-Waller parameter, B _eff, and lattice strain, , were evaluated on a natural pyrite (FeS₂) after grinding. The effective Debye-Waller parameter, B _eff, which depends on the displacement of atoms in the crystal, was calculated for the overall crystal, B _eff(FeS₂), and for sulphur, B _eff(S), from the intensities of the X-ray diffraction lines. The B _eff(S) increased markedly with increasing grinding time, while B _eff(FeS₂) did not change significantly. The lattice strain, , was not recognized. These observations suggest that the displacement of sulphur atoms preferentially takes place by grinding. The relations between these B _eff values and crystallite size, L, were observed to be common for two different methods of grinding. This tendency was considered to be an inherent property of pyrite. The value of B _eff(S) is a useful index to estimate mechanically caused strain in pyrite.     

Red-emitting alkaline-earth rare-earth pentaoxometallates powders prepared by metal carboxylates solution

Moisture-insensitive metal carboxylates that are mostly liquids at room temperature have been first applied to the preparation of strontium europium aluminate (Sr₂EuAlO₅) powders for red-emitting phosphor under near ultraviolet radiation. Strontium naphthenate, aluminium-2-ethylhexanoate and europium-2-ethylhexanoate were dissolved with toluene to prepare starting solution. Precursor pyrolyzed at 500 °C for 240 min was finally annealed at 900–1200 °C for 240 min in Ar. X-ray diffraction analysis, field emission–scanning electron microscope and fluorescent spectrophotometer were used to evaluate structural and optical properties. For the 1000 °C-annealed powders with regular shape and narrow size distribution confirmed by FE–SEM observation, strong red emission at 615 nm under the excitation of 395 nm maximum was reached, then the higher annealed samples at above 1100 °C gave the lower emission intensities.     

Preparation and characterization of Eu<Superscript>3+</Superscript> activated CaSiO<Subscript>3</Subscript>, (CaA)SiO<Subscript>3</Subscript> [A = Ba or Sr] phosphors

Eu³⁺ activated CaSiO₃, (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ have been prepared by sol-gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu³⁺ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to⁵D₀ →⁷F₂ transition of Eu³⁺ ion in (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ phosphors, when excited by 254 nm. The (Ca, Ba) SiO₃ material is proposed as an efficient red phosphor.     

Hydrothermal synthesis and luminescence of MWO4:Tb3+ (M = Ca,Sr, Ba) microsphere phosphors

Spherical MWO₄:Tb³⁺ (M = Ca, Sr, Ba) particles were synthesized by a hydrothermal route at 180 °C for 10 h. The synthesized MWO₄:Tb³⁺ particles were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and luminescence spectroscopy. The XRD and FT-IR results show that MWO₄:Tb³⁺ particles with a scheelite-type crystal structure were synthesized successfully. The SEM and TEM results show that uniform spherical particles in the range of hundreds of nanometers were obtained. The possible growth mechanism may be attributed to a typical Ostwald ripening process. The excitation spectra of MWO₄:Tb³⁺ phosphors show a strong absorption band of the WO₄ ^2? group and some weak absorption bands of Tb³⁺ ions. The emission spectra of MWO₄:Tb³⁺ phosphors show the characteristic emission bands of Tb³⁺ ions. CaWO₄:Tb³⁺ sample has the highest excitation and emission intensity.     

The effects of oxygen-catalysed and heat treatment on the precipitation synthesised ZnO nanoparticles

Nanocrystalline ZnO particles prepared by precipitation method from Zn and I₂ reaction with oxygen as catalyst were investigated. The addition of diethanolamine (DEA) as capping agent and fast pyrolysis treatment at 550, 700 and 850?°C were also characterised and elaborated. Compact and small spherical particles were observed for ZnO synthesised with O₂ catalysed whilst, uneven surface, fewer dense packing particles and macropore structures were observed for ZnO prepared without excess of O₂. It was shown that diffusion of O₂ has improved the structural and photoluminescence behaviour of the prepared ZnO nanoparticles. ZnO synthesised with O₂-catalysed exhibited better crystalline and leaned towards a pure state as shown by shifting of PL peak to higher energy of pure ZnO while, sample prepared without excess of O₂ exhibits poor crystalline and decreasing of the energy band gap with respect to increment of calcination temperatures. Single violet emission was observed in all samples synthesised with excess of O₂ whereby the highest intensity was obtained by calcining at 850?°C with photon energy at 2.95 eV. In contrast to sample with excess of O₂, ZnO calcined without excess of O₂ at 850?°C displays violet and green emission with energy at 2.93 eV and 2.35 eV, respectively.     

Preparation and luminescent properties of Eu-doped BaTiO3 thin films by sol–gel process

Eu-doped BaTiO₃ thin films with a pseudo-cubic perovskite structure were successfully fabricated on magnesia substrates at low temperature by using a high-concentration sol–gel process, in which the newly developed gel-aging process on substrate was employed. Film microstructure, crystallinity, sintering properties and photoluminescence (PL) were investigated. The xerogel thin films exhibited strong PL associated with Eu³⁺ ions under ultraviolet excitation at room temperature; the PL was visible to naked eyes. The intensity maximum of PL was reached with doping concentration of about 8 mol%. Sintering above 600 °C caused reduction of europium, resulting in a rapid quenching of Eu³⁺ emission and enhancement of Eu²⁺ emission.     

Synthesis and characterization of Yb3+,Tm3+:Ba2YF7 nanocrystalline with efficient upconversion fluorescence

A novel upconversion luminescence nanocrystals Yb³⁺,Tm³⁺:Ba₂YF₇ were synthesized via the hydrothermal method. They have uniform morphology with a mean size of 30 nm even if annealed at 600 °C. Pumped by 980 nm laser diode the as-synthesized powers emit ultraviolet/blue light, which is in the range of the specific upconversion luminescent spectra of Tm³⁺ ions. After post-annealing at 600 °C in an argon atmosphere for 2 h, their upconversion luminescence intensity is 5 multiple improved and the ultraviolet/blue light can even be seen by the naked eyes under a low excitation power of 20 mW. This indicates that Ba₂YF₇ is a very effective luminescent host material. Excitation power dependences of individual upconversion emission intensity are plotted, which partly uncover the upconversion luminescence mechanism of Tm³⁺ ions.     

Effective Debye-Waller parameter of carbons

The effective Debye-Waller parameters,B _eff, were determined along thec- anda-axes on two kinds of coke and a thermal black with different heat-treatment temperatures. FromB _eff values at room temperature and around 90 K, the dynamic component,B _d, and the Debye temperature, _D, for the thermal vibration of atoms, and the static component,B _S, due to static displacement of atoms, were determined separately. The development of graphite structure detected by the decreases in interlayer spacing,d ₀₀₂ and the growth of crystallites caused decreases in bothB _d andB _S. The thermal black had a much largerB _d andB _s, which was probably caused from retention of its spherical particles even after heat-treatment at high temperatures. The Debye temperature for the in-plane vibration, [_1D] _a , increased remarkably with the decrease ind ₀₀₀₂, and that for the out-of-plane vibration, [_D] _c , increased slightly, which corresponded to a remarkable increase in anisotropy with heat treatment. The Debye temperatures showed apparent dependences onB _s which could be extrapolated to the Debye temperatures alonga- andc-axes for the single crystal graphite atB _s = 0. The present results on Debye-Waller parameters agree with the results on structural studies obtained by X-ray diffraction and high resolution electron microscopy.     

Debye-Waller parameters of diatomic crystals

The Debye-Waller parameters, the effective valuesB _eff, the dynamic component,B _d, and the static component,B _s, of each constituent atom and also of the bulk were measured for some diatomic crystals with NaCl- and zinc blende-type structures. The dominant effect of heavy constituent atoms on the dynamic component of bulk crystals was found, and the mean square displacement in bulk crystals was approximated well by the atomic mass averaged mean square displacements of the constituent atoms. A remarkable effect of structural defects onB _eff, particularly onB _s, was observed in NiO samples with different degrees of non-stoichiometry. The different extents of the SiC-forming reaction between solid carbon and fused silicon resulted in quite differentB _eff values; the larger theB _eff value the smaller the extent of the reaction.     

UV and VUV characteristics of (YGd)2O3:Eu phosphor particles prepared by spray pyrolysis from polymeric precursors

Red-emitting (YGd)₂O₃:Eu phosphor particles, with high luminescence efficiency under vacuum ultraviolet (VUV) and ultraviolet (UV) excitation, were prepared by a large-scale spray pyrolysis process. To control the morphology of phosphor particles under severe preparation conditions, spray solution with polymeric precursors were introduced in spray pyrolysis. The prepared (YGd)₂O₃:Eu phosphor particles had spherical shape and filled morphology even after post-treatment irrespective of Gd/Y ratio. In the case of solution with polymeric precursors, long polymeric chains formed by esterification reaction in a hot tubular reactor; the droplets turned into viscous gel, which retarded the precipitation of nitrate salts and promoted the volume precipitation of droplets. The brightness of (YGd)₂O₃:Eu phosphor particles increased with increasing gadolinium content, and the Gd₂O₃:Eu phosphor had the highest luminescence intensity under UV and VUV excitation. The maximum peak intensity of Gd₂O₃:Eu phosphor particles under UV and VUV were 118 and 110% of the commercial Y₂O₃:Eu phosphor particles, respectively.     

Structure and luminescence properties of TiO2:Er3+ nanocrystals annealed at different temperatures

Erbium doped TiO₂ nanocrystals with the structures of anatase, pyrochlore Er₂Ti₂O₇, and rutile, characterized by X-ray diffraction, have been obtained at different annealing temperatures from 300 °C to 900 °C. The nanocrystalline size for anatase TiO₂ is reduced with increasing doped erbium concentration. Following ultraviolet 325 nm irradiation, the intensity of the green emission is the most intense for the TiO₂:Er³⁺ nanocrystals with a structure of pyrochlore Er₂Ti₂O₇, which evolves from the structure of anatase annealed at 800 °C. Moreover, following ultraviolet 325 nm and infrared 980 nm irradiation, the visible emission spectra for the nanocrystals annealed at 900 °C change drastically. Correspondingly, the structure of anatase disappears, while that of rutile becomes dominant, which indicates that phase transformation occurs.     

Thermostimulated exoelectron emission during the structural transition in Ca10(PO4)6(OH)2

Thermostimulated exoelectron emission (TSEE) from a biocompatible calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (CHA) was studied in a temperature range from 20 to 400°C. It was established that the structural transition in CHA is manifested by a sharp increase in the exoelectron emission intensity beginning at 200°C, followed by a peak in the TSEE spectrum.     

Superfine Sr2CeO4 powder with blue-emission prepared by microemulsion method

Powder samples of Sr₂CeO₄ were prepared by microemulsion-heating method. Field emission scanning electron microscopy (FE-SEM) images showed that the sample fired at 850 °C for 4 h was spherical with an average diameter of 70∼80 nm while the samples which sintered at 900 °C for 4 h and 1000 °C for 4 h were shuttle-like shape and spherical respectively both with sizes less than 1 μm. X-ray diffraction (XRD) patterns disclosed that the superfine Sr₂CeO₄ exhibited an orthorhombic crystal structure. Room-temperature photoluminescence (PL) analysis indicated that there were three excitation peaks located at around 260, 280, and 350 nm, and all the Sr₂CeO₄ samples showed intensely blue emission at 470 nm. Compared with Sr₂CeO₄ samples prepared with other methods, the Sr₂CeO₄ phosphor fabricated with this method had a controllable shape with smaller size, lower calcination temperature, and shorter calcinations time.     

Preparation and phase development of yttria-doped ceria coated TZP powder

This paper presents a simple technique for preparation of yttria-doped ceria (YDC) coated tetragonal zirconia polycrystal (3Y-TZP) powder and its phase development upon firing. The coating solution was prepared using yttrium nitrate hexahydrate and cerium nitrate hexahydrate as starting reagents. Thermochemical reactions of the coated powder were studied using TGA and FTIR while phase development upon firing was examined using XRD. Inward diffusion of the coating YDC into the TZP particles was monitored by observing the change of crystal structure and lattice parameter as a function of sintering temperature and time. At sintering temperature of 1300 °C for 1 h, crystal structure of the sample was still tetragonal (t-ZrO₂). Increasing sintering time to 5 h at 1300 °C, diffusion of YDC into TZP particles occurred drastically and the structure was changed to cubic (c-ZrO₂) as indicated by the disappearance of (002)/(200) peak splitting. Increasing sintering temperature to 1400 and 1500 °C, however, resulted in the co-existence of tetragonal and cubic phases as indicated by the appearance of triples around 72.5–74° 2θ and also the decrease of cubic lattice parameter. When the sintering temperature was further increased to 1600 °C, lattice parameter was only slightly changed, suggesting that inward diffusion of YDC reached saturation point around this temperature.     

Phase transition and optical properties of Ge doped ZnO films synthesised by sputtering

Ge doped ZnO films were deposited on Si substrates by sputtering technique. With the increasing annealing temperature, the crystal quality of samples becomes gradually better and the phase transition can be observed at annealing temperature of 600°C. X-ray photoelectron spectroscopy results show the incorporation of Ge into the ZnO films with 14·81 at-%Ge content. Fourier transform infrared spectroscopy absorption spectra of samples annealed at above 600°C display vibration mode of ν (ZnO₄) and ν (GeO₄) in Zn₂GeO₄. The enhancement of ultraviolet emission intensity should be attributed to the yielded mass holes caused by Ge doping and the rising crystal quality. The sample annealed at 800°C displays the strongest blue emission due to the native defects in Zn₂GeO₄ films or/and surface defects.     

Effect of metal halide fluxes on the microstructure and luminescence of Y3Al5O12:Ce phosphors

Yellow-emitting Y_2.95Al₅O₁₂:0.05Ce (YAG:Ce) phosphor particles with high luminescence efficiency under 450 nm ultraviolet (UV) excitation were prepared by a heat treatment of submicrometer-sized oxide powder mixture in a reducing atmosphere at 1550 °C. Prior to the heat treatment, the oxide mixture was blended with 5 wt% of metal halides – BaF₂, BaCl₂, NaF, NaCl, and KF – as a flux. It was observed that YAG:Ce particles prepared with fluorine containing flux demonstrated spherical morphology, high photoluminescence properties, and diameters of 5–20 μm, whereas those prepared with chlorine were small-sized particles (≤5 μm) with relatively low intensity. The highest relative photoluminescence (PL) intensity (∼118%) was obtained for the samples prepared with 5% BaF₂. A set of rules was established for the formation of spherical YAG:Ce particles in the presence of this flux.     

Microwave hydro/solvothermal synthesis of octahedron-like NaEu(MoO4)2 microarchitectures by EDTA-assisted and photoluminescence property

Octahedron-like NaEu(MoO₄)₂ microarchitectures with tetragonal scheelite-type structure have been successfully synthesized by a facile ethylene diamine tetraacetic acid (EDTA)-mediated microwave hydrothermal method. The as-prepared products were characterized by X-ray diffractometer, scanning electron microscope and photoluminescence. The particle size and morphology of NaEu(MoO₄)₂ can be tuned effectively by adjusting reaction temperature, reaction time, the amount of EDTA and ethylene glycol. Remarkably, the morphologies were the microflakes, micro-octahedrons, when the amount of EDTA was increased from 0 to 0.01 g at 180 °C. The excitation spectrum of the calcined NaEu(MoO₄)₂ micro-octahedron was observed with a maximum peak at near ultraviolet excitation (λex = 393 nm). Its emission spectrum was recorded under a excitation wavelength of 393 nm and exhibited the most intensitive red emission at 615 nm. This indicates the photoluminescence properties were strongly dependent on crystal morphology and crystallinity. So the calcined NaEu(MoO₄)₂ micro-octahedron has the potential to be applied in many LED devices.     

Preparation of hollow hydroxyapatite microspheres

The preparation of hollow hydroxyapatite (HA) microspheres as potential drug-delivery vehicles was investigated. A lithium-calcium-borate (10Li₂O-15CaO-75B₂O₃) (mol%) glass, made by fusing the components at 1100°C for 1 h, was ground to a powder and passed through a flame at ∼1400°C to spheroidize the particles. The resulting glass microspheres (106–125 μm in diameter) were reacted in 0.25 M K₂HPO₄ solution for 5 days at 37°C and pH 10–12, resulting in the formation of porous, hollow microspheres of a calcium phosphate (Ca-P) material with external diameters similar to those of the original glass particles. Heat treatment at 600°C for 4 h partially converted the Ca-P material to HA, as confirmed by X-ray diffraction, and also increased the strength of the hollow microspheres.     

Enhanced emission and improved thermal stability of BaMgAl10O17:Eu2+ phosphor via additional Mg2+ doping

BaMgAl₁₀O₁₇:Eu²⁺ doped with 0–6% additional Mg²⁺ were synthesized by co-precipitation method. Their photoluminescence and thermal stability were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The additional Mg²⁺-doped samples exhibited stronger emission intensity and better thermal stability than the sample without additional Mg²⁺ under 254 or 147 nm excitation. After thermal degradation, the 4% additional Mg²⁺-doped sample had the highest emission intensity which was 12.7% and 16.6% stronger than that of the sample without additional Mg²⁺ under 254 and 147 nm excitation, respectively. Moreover, the improvement mechanisms on emission intensity and thermal stability were discussed.     

Preparation and properties of calcium oxide from eggshells via calcination

Duck eggs are one of the most versatile cooking ingredients in which residue eggshells are discarded. Raw duck eggshells were calcined at temperatures between 300 to 900 °C, for 1, 3, and 5 h. Both the raw and calcined duck eggshells were characterized by FTIR, STA, XRD, XRF, TEM, BET, a particle size analyzer, and an impedance analyzer. The proper calcination conditions are: 900 °C and 1 h, yielding calcium oxide with a purity of 99.06 % w/w. The calcium carbonate of the rhombohedral form (CaCO₃) transforms completely into the calcium oxide or lime of the face centered cubic form (CaO) at 900 °C, as shown by XRD diffraction patterns. The transmission electron microscopy (TEM) images of the calcium oxide reveal a moderately good dispersion of nearly uniform particles. The calcium oxide has a white color, a spherical shape, high porosity, and narrow particles size distribution. The percentage of ceramic yield of the calcium oxide is 53.53, as measured by STA (TG-DTA-DTG). The calcium oxide has a N₂ adsorption-desorption isotherm indicating the meso-porosity range. The dielectric constant and the electrical conductivity of the calcined calcium oxide are 35 and 1:0×10^?6(??·m)^?1, respectively, at the frequency of 500 Hz.