Monoclinic HfO2:Eu X-ray phosphor

HfO₂ and HfO₂:Eu powders were synthesized with Pechini method at temperatures in the range of 600–1500 °C. Structural, radioluminescence and photoluminescence properties of the powders were investigated. The highest light output of about 20% of the efficiency of commercial GOS:Eu was found for materials containing 0.5% of Eu and prepared at 1500 °C. The data shows, that further improvement of light output could be obtained if materials are processed at yet higher temperatures. Emission spectra indicate that Eu³⁺ experiences variety of symmetries of its surroundings. Undoped materials produce broad band emission peaking at 480 nm and showing a significant afterglow.     

Fabrication and spectroscopic properties of nanocrystalline La2Hf2O7:Pr

La₂Hf₂O₇ nanopowders doped with different Pr concentrations (0.05–10 mol.%) were synthesized by the Pechini method. XRD measurements confirmed the single crystalline phase formed already at 800 °C and the structure was cubic pyrochlore. Luminescence excitation and emission as well as radioluminescence spectra were recorded for the materials. Both optical and X-ray excitation of La₂Hf₂O₇:Pr produced a red emission resulting from the 4f–4f transitions of Pr³⁺ ions. Luminescence of materials synthesized at low temperatures was characterized by broadband glass-type emissions, while heat treatment at 1400 °C led to spectra showing the typical for crystalline hosts narrow and intense 4f–4f transitions of Pr³⁺.     

Synthesis and characterization of nanocrystalline HAp powders prepared by using aloe vera plant extracted solution

Nanocrystalline hydroxyapatite (HAp) powders were synthesized by a simple method using aloe vera plant extracted solution. To obtain nanocrystalline HAp, the prepared precursor was calcined in air at 400–800 °C for 2 h. The phase composition of the calcined samples was studied by X-ray diffraction (XRD) technique. The XRD results confirmed the formation of HAp phase. With increasing calcination temperature, the crystallite of the HAp increased, showing the hexagonal structure of HAp with the lattice parameter, a, in a range of 0.9520–0.9536 nm and c of 0.6739–0.6928 nm. The particle sizes of the powder were obtained to be 43–171 nm. The optical properties of the calcined powders were characterized by Raman and FTIR spectroscopies. The Raman spectra showed a main peak of the phosphate vibration mode (ν₁(PO₄)) at ∼963 cm⁻¹ for all the calcined samples. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the calcined powders. The morphology tends to change from a spherical shape to a rod-like shape with increasing calcination temperature as revealed by TEM.     

Structure dependent luminescence characterization of green–yellow emitting Sr2SiO4:Eu2+ phosphors for near UV LEDs

This paper reports on the luminescence properties of mixtures of α- and β-(Sr_0.97Eu_0.03)₂SiO₄ phosphors. These phosphors were prepared by 3 different synthesis techniques: a modified sol–gel/Pechini method, a co-precipitation method and a combustion method. The structural and optical properties of these phosphors were compared to those of solid state synthesized powders. The emission spectra consist of a weak broad blue band centered near 460 nm and a strong broad green–yellow band centered between 543 and 573 nm depending on the crystal structure. The green–yellow emission peak blue-shifts as the amount of β phase increases and the photoluminescence emission intensity and quantum efficiency of the mixed phase powders is greater than those of predominant α-phase powders when excited between 370 and 410 nm. Thus, (Sr_1?xEu_x)₂SiO₄ with larger proportion of the β phase are more promising candidates than single α-phase powders for use as a green–yellow emitting phosphor for near UV LED applications. Finally the phosphors prepared by the sol–gel/Pechini method, which have larger amount of β phase, have a higher emission intensity and quantum efficiency than those prepared by co-precipitation or combustion synthesis.     

Electronic structure and optical properties of BaMoO4 powders

Barium molybdate (BaMoO₄) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 °C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm⁻¹, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO₄] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.     

Microstructure and dielectric properties of PMN–PT ceramics prepared by the molten salts method

The sintering characteristic and dielectric properties of 0.67PMN–0.33PT ceramics prepared by the molten salt synthesis (MSS) method were investigated. PMN–PT particles synthesized by MSS with smaller grain size and good dispersion could lower the sintering temperature of ceramics; PMN–PT ceramics with relative density above 96% could be obtained in the range 1150–1180 °C. The molten salts species could significantly affect the microstructure and properties of MPN-PT ceramics. In the range 1100–1200 °C, PMN–PT ceramics from the sulfate flux MSS powders showed intergranular fracture, but that from the chloride flux MSS powder showed transgranular fracture. At the same sintering condition, the properties of PMN–PT ceramics from the powders prepared in the chloride flux are better than that from the powders prepared in the sulfate flux, their maximum dielectric constant ε_max≈29,385 and piezoelectric constant d₃₃≈660 pC/N. The above results demonstrated that PMN–PT ceramics prepared by the molten salts method possessed excellent piezoelectric and dielectric properties.     

Preparation and properties of transparent SnO–P2O5 glasses

Colorless, transparent SnO–P₂O₅ (SP) glasses with 60–70 mol% SnO compositions were prepared by melting at 880–1000 °C in Ar atmosphere using commercial SnO and P₂O₅ powders as raw materials and vitreous carbon crucibles. SP glasses are characterized by glass transition temperature, onset of crystallization, thermal expansion coefficient and weight loss after immersion test. The viscosity of 67SnO–33P₂O₅ glass was measured by a penetration method in the range of 10^7.9–10^10.5 Pa s at 267–290 °C. The results of optical properties show that the transparent SP glasses have high refractive indexes over 1.75 and high transmission over 80% in the visible and IR region of 380 and 2700 nm.     

A new reaction: vacuum synthesis and characterization of IONO2 and IONO

The new reactions for preparing IONO₂ and IONO have been found. IONO₂ and IONO can be easily prepared in vacuum by the heterogeneous reactions of gaseous ICl over the solid powders AgNO₃(s) at the room temperature and AgNO₂(s) at 0(±1) °C which were loosely filled into the quartz inlet tube (about 1.5 cm inside diameter and 5 cm long) and supported on the quartz wool, respectively, and then are characterized well by the PES experiment and the ROVGF calculations.     

Preparation and characterization of iron/titanium-oxide composite particles

The iron/titanium-oxide composite particles have been prepared using “in-situ” hydrogen-thermal reduction method. The composites were characterized by X-ray diffraction, physical property measurement system and Mössbauer spectroscopy. The powder X-ray diffraction patterns reveal the presence of crystalline α-iron and titanium-oxide (FeTiO₃/TiO₂). The Mössbauer spectra of powders have been measured at room temperature, which indicated that the α-iron and the high-spin iron(II/III) components were observed. The complex permittivity and permeability of the composites have been measured using vector network analyzers. Reflection loss of the iron/titanium-oxide composite powders dispersing in epoxy resin has been calculated using measured values of complex permittivity and permeability in the frequency range of 2–12 GHz. The maximum reflection loss of ?36 dB was observed at 5.0 GHz. This study shows the possibility to obtain the novel dielectric and magnetic based microwave absorbers.     

The comparison of Ag–As33S67 films prepared by thermal evaporation (TE), spin-coating (SC) and a pulsed laser deposition (PLD)

Chalcogenide thin films could be prepared by many experimental methods resulting in some differences in structure and physicochemical properties of prepared films. In this work, the As₃₃S₆₇ amorphous films were prepared by three different preparation techniques: vacuum thermal evaporation (TE), pulsed laser deposition (PLD) and spin-coating (SC). A silver film was deposited on the top of the As₃₃S₆₇ films and photodoped.The X-ray diffraction analysis showed significant differences in arrangement between bulk glass and thin films and also among films themselves. The Raman spectroscopy showed that the Raman spectra of PLD film and bulk glass are almost similar. On the other hand, TE films contain higher amount of homopolar bonds As–As and S–S. The value of refractive index of As₃₃S₆₇ bulk glass was 2.31. All prepared films have lower index of refraction contrary to bulk glass, i.e. TE∼2.27, PLD∼2.20 and SC∼1.90. The increase of refractive index with silver concentration is shown either. The optical bandgap of undoped As–S prepared films was different: TE∼2.42 eV, PLD∼2.45 eV and SC∼2.54 eV.     

Study of microstructure,impedance and dc electrical properties of RuO2–spinel based screen printed ‘green’ NTC thermistor

The NTC powder materials were prepared chemically using acetates of (Mn–Co–Ni), as precursor materials. The sintering of the powders shows the existence of spinel phases at comparatively low temperature, i.e. 800 °C. ‘Green’ thick films were prepared by admixing of the spinel powder, RuO₂, lead free glass frit and the organic vehicle. Synthesized powders as well as the thermistor films were characterised by FTIR spectroscopy, TG/DTA, XRD and SEM. The electrical parameters like sheet resistance, thermistor constant, temperature co-efficient of resistance of the thick film thermistors are presented. The impedance of the thermistor films was measured and it has been correlated with the theoretical model and its equivalent circuit using the ‘Cole–Cole’ plots.     

Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH₃OH, have been determined near 3.4 and 10 μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015 cm^?1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50–760 Torr and 204–296 K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10 μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.     

Design of europium doped SiO2–TiO2 hybrids as novel luminescent photocatalyst

SiO₂/TiO₂:Eu³⁺ composite materials were facially prepared by the sol–gel technique and all the as-derived powders exhibited europium characteristic red emissions under multiple excitation wavelengths extended to visible range (395 and 465 nm). The influence factors such as Si/Ti ratio, orders of hydrolysis, annealing temperature and doping concentration were systematically studied. The novel photocatalytic behavior for removing phenol was thoroughly investigated.     

Effect of CuI on the formation and properties of Te-based far infrared transmitting chalcogenide glasses

A series of Ge–Te–CuI far infrared transmitting chalcohalide glasses were prepared by traditional melt-quenching method and the glass-forming region was determined. Properties measurements include density, DTA, XRD, SEM, Vis–NIR and infrared (IR) transmission spectra. The results show that with the addition of CuI, the glass-forming ability is improved and nearly 30 mol% CuI can be dissolved into the Ge₂₀Te_80?x(CuI)_x glass system. The density and glass transition temperature of Ge–Te–CuI chalcohalide glasses are within the range 5.459–5.960 g cm^?3 and 150–184 °C, respectively. These glasses all have wide optical transmission window from 1.8 to 25 μm and offer an alternative solution for far infrared transmitting materials.     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Effect of strontium addition on europium-doped ceria properties

Nanopowders of composition Ce_0.9(Eu_1 ? xSr_x)_0.1O_2 ? δ (x = 0, 0.1, 0.3, 0.5, and 0.7) were prepared by the Pechini method. The microstructure and properties of powders and sintered ceramics are discussed in this paper. X-ray diffraction (XRD) and Raman spectroscopy revealed that all powders calcined at 550 °C were single phase, with the cubic fluorite-type structure. The good sintering properties of the synthesized nanopowders allowed us to obtain dense ceramics (> 96% theoretical density). Dense ceramics with density higher than 96% of the theoretical value were obtained without the need of sintering aid. The morphology of the sintered ceramics was evidenced by scanning electron microscopy (SEM). The ionic conductivities of doped and co-doped ceria ceramics were investigated as a function of temperature by using AC impedance spectroscopy in the temperature range 250–800 °C. Impedance spectra indicate a significant diminution of grain boundary resistance after partial substitution of Eu with Sr in europia-doped ceria sample, especially in the low and intermediate-temperature range. The best conductivity was evidenced for the Ce_0.9Eu_0.09Sr_0.01O_2 ? δ composition.     

Microwave-induced combustion synthesis of Ni–Zn ferrite powder and its characterization

Ni–Zn ferrite powders were successfully synthesized by microwave-induced combustion process. The process takes only a few minutes to obtain calcined Ni–Zn ferrite powders. The resultant powders were investigated by XRD, SEM, VSM, TG/DTA and surface area measurements. The as-received product shows the formation of cubic ferrite with saturation magnetization (M_s)≈23 emu/g, whereas upon annealing at 850°C for 4 h, the saturation magnetization (M_s) increased to ≈52 emu/g.     

Synthesis of Co nanocapsules coated with BN layers by annealing of KBH4 and [Co(NH3)6]Cl3

Cobalt (Co) nanocapsules coated with boron nitride (BN) layers were synthesized by annealing of ammine complex. KBH₄ and [Co(NH₃)₆]Cl₃ were used as starting materials, and annealed these powders at 500–1000 °C with flowing nitrogen gas. Formation of fcc-Co nanocapsules coated with BN layers was observed from X-ray diffraction patterns and high-resolution electron microscopy. Particle size of fcc-Co prepared at 1000 °C with flowing 100 sccm N₂ gas was approximately 40 nm, and the values of saturation magnetization and coercivity were 74.5 emu/g and 88 Oe, respectively. Good oxidation- and wear-resistances were obtained by encapsulating Co nanoparticles with BN layers.     

Intercalation of esters into vanadyl phosphate

Intercalates of vanadyl phosphate with formates and acetates of C₁–C₈ alcohols and dimethylesters of dicarboxylic acids C₂–C₆ were prepared by a displacement reaction of 2-propanol-intercalated VOPO₄. The diffractograms of the intercalates show a series of sharp (0 0 l) reflections, (2 0 0) reflection and in some cases several (h k l) lines with low intensity. The tetragonal lattice parameters of the intercalates were calculated. The intercalates prepared are not stable in air. The C=O stretching vibration in IR spectra of the intercalates prepared was shifted to lower wavenumbers in comparison with the spectra of the pure guests, indicating that all esters are anchored to the host layers by their carbonyl oxygen.     

Coercivity variations with Pr- and Zr-substituted NdDyFeB-based HDDR powders

As part of an industry-based project, we studied the effects of Pr and Zr substitutions to a basic Nd₁₅DyFe₇₆B₈ material. We processed the materials using a conventional hydrogenation-disproportionation-desorption-recombination (HDDR) process and a simple rotary-pump vacuum; however, we also experimented with high-vacuum conditions in order to see what effect these had. The Pr and Zr substitutions were observed to have a positive and cost-effective influence on the coercivity of the processed powders: the optimum Pr substitution was the replacement of three-quarters of the neodymium, and for Zr, a much smaller 0.1 at% was found to be the best.Microstructural observations of the as-cast structures revealed significant differences between the Zr- and Pr-substituted materials and the additive-free NdDyFeB alloy, but post-HDDR microstructures were all very similar and provided little help for optimizing the processing conditions. By combining the substitutions of Pr and Zr in a relatively rare-earth-rich alloy, we were able to produce a coercive powder of >1000 kA/m and have a process which can now be quickly and easily transferred to the factory.