Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

Ce and Eu activated Na<Subscript>2</Subscript>Zn<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>4</Subscript>, a new promising novel phosphor

A new efficient phosphor, Eu²⁺/Eu³⁺ and Ce³⁺ activated Na₂Zn₅(PO₄)₄ has been synthesized by solid-state reaction technique at high temperature. X-ray powder diffraction analysis confirmed the formation of Na₂Zn₅(PO₄)₄ host lattice. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 0·5–2 μm. Photoluminescence excitation spectrum measurements of Ce³⁺ activated Na₂Zn₅(PO₄)₄ show that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the visible (blue) range due to the 5d-4f transition of Ce³⁺ ions which is applicable for scintillation purpose, whereas Eu²⁺/Eu³⁺ activated Na₂Zn₅(PO₄)₄ phosphor emits blue, green and red emission spectrum shows at 487 nm, 546 nm with a dominant peak at 611 nm respectively, due to Eu²⁺/Eu³⁺ ions which is promising candidate for solid state lighting. Therefore, newly synthesised, by low cost and easy technique prepared, novel phosphors may be useful as RGB phosphor for solid state lighting application.     

Structure and microwave dielectric properties of ZnTa<Subscript>2</Subscript>O<Subscript>6</Subscript> ceramics with TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript> additions

Ceramic samples based on ZnTa2O₆ and ZnTa₂O₆–MO₂ (M = Ti, Zr) systems have been obtained by the solid state ceramic route. The phase composition and microstructure of samples were investigated. The effect of the aliovalent substitution of ions Zn²⁺ and Ta⁵⁺ by M⁴⁺ (M = Ti, Zr) in the structure of ZnTa₂O₆ on microwave dielectric properties of ceramics was studied. The way of the compensation of the positive temperature coefficient of resonant frequency of dielectric resonators based on ZnTa₂O₆ ceramics with using the aliovalent substitution of cations was proposed. Dielectric resonators with the high temperature stability of the resonant frequency and high dielectric properties in the microwave range based on the ZnTa₂O₆–ZrO₂ system were obtained for application in electronics.     

Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

The comparison: photoluminescence and afterglow behavior in CaSnO<Subscript>3</Subscript>:Dy<Superscript>3+</Superscript> and Ca<Subscript>2</Subscript>SnO<Subscript>4</Subscript>:Dy<Superscript>3+</Superscript> phosphors

This paper reports the comparison of photoluminescence and afterglow behavior of Dy³⁺ in CaSnO₃ and Ca₂SnO₄ phosphors. The samples containing CaSnO₃ and Ca₂SnO₄ were prepared via solid-state reaction. The properties have been characterized and analyzed by utilizing X-ray diffraction (XRD), photoluminescence spectroscope (PLS), X-ray photoelectron spectroscopy (XPS), afterglow spectroscopy (AS) and thermal luminescence spectroscope (TLS). The emission spectra revealed that CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed different photoluminescence. The Ca₂SnO₄:Dy³⁺ phosphor showed a typical ⁴F_9/2 to ⁶H_j energy transition of Dy³⁺ ions, with three significant emissions centering around 482, 572 and 670 nm. However, the CaSnO₃:Dy³⁺ phosphor revealed a broad T₁ → S₀ transitions of Sn²⁺ ions. The XPS demonstrate the existence of Sn²⁺ ions in CaSnO₃ phosphor caused by the doping of Dy³⁺ ions. Both the CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed a typical triple-exponential afterglow when the UV source switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors was generated by the suitable electron or hole traps which were resulted from the doping the calcium stannate host with rare-earth ions (Dy³⁺).     

Phase conversion and spectral properties of long lasting phosphor Zn<Subscript>3</Subscript> (PO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Mn<Superscript>2+</Superscript>, Ga<Superscript>3+</Superscript>

A red long lasting phosphor Zn₃(PO₄)₂:Mn²⁺,Ga³⁺ (ZPMG) was prepared by ceramic method, and phase conversion and spectral properties were investigated. Results indicated that the phase conversion from α-Zn₃(PO₄)₂, β-Zn₃(PO₄)₂ toγ-Zn₃(PO₄)₂ occurs with different manganese concentration incorporated and sinter process. The structural change induced by the phase transformation results in a remarkable difference in the spectral properties. The possible luminescence mechanism for this red LLP with different forms has been illustrated.     

SnO<Subscript>2</Subscript>(Au<Superscript>0</Superscript>, Co<Superscript>II,III</Superscript>) nanocomposites: A synergistic effect of the modifiers in CO detection

Nanocrystalline SnO₂ has been synthesized and its surface has been modified with Au⁰ and Co(II, III). The distribution of the modifiers over the nanocomposites has been studied by X-ray diffraction, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The effect of the modifiers on the hydrogen reduction of nanocrystalline SnO₂ has been assessed. The CO sensing properties of the synthesized materials (10 ppm CO in air) have been studied in situ by electrical conductance measurements. The addition of both Au⁰ and Co(II, III) allows the working temperature of the SnO₂-based semiconductor sensor to be lowered to 215°C.     

Synthesis and x-ray diffraction study of solid solutions in the Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>TiO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>ZrO<Subscript>4</Subscript> system

The multicomponent refractory oxide system Zn₂(Ti_aSn_b)_{1 ? x} Zr_xO₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 1: 0, 2: 1, 3: 1, 4: 1; x = 0?1.0; Δx = 0.05) has been studied by x-ray diffraction, using samples prepared by melting appropriate oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions of different compositions.     

Microstructure and dielectric properties of BaTiO<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>-SnO<Subscript>2</Subscript> ceramics

We have studied the effect of codoping with CeO₂ and SnO₂ (2 to 3.5 wt %) on the microstructure and dielectric properties of BaTiO₃. Doping with CeO₂ and SnO₂ inhibits grain growth in BaTiO₃ and enables the fabrication of ceramic materials with a grain size below 1 μm. The temperature coefficient of permittivity of the ceramics increases with CeO₂ + SnO₂ content, firing temperature, and firing time.     

Structural,dielectric, ac conductivity and electromagnetic shielding properties of polyaniline/Ni<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

A conducting polymer, polyaniline (PANI)/Ni_0.5Zn_0.5Fe₂O₄ composites with high dielectric absorbing properties and electromagnetic shielding effectiveness at low frequencies were successfully synthesized through a simple in situ emulsion polymerization. PANI was doped with hydrochloric acid to improve its electrical properties and interactions with ferrite particles. PANI/Ni_0.5Zn_0.5Fe₂O₄ composites were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. Frequency dependence of dielectric and ac conductivity (σ_ac) studies have been undertaken on the PANI/Ni_0.5Zn_0.5Fe₂O₄ composites in the frequency range 50 Hz–5 MHz. The electrical conduction mechanism in the PANI/Ni_0.5Zn_0.5Fe₂O₄ is found to be in accordance with the electron hopping model. Further, frequency dependence of electromagnetic interference (EMI) shielding effectiveness (SE) is studied. The EMI shielding effectiveness is found to decrease with an increase in the frequency. The maximum value 55.14 dB of SE at 50 Hz was obtained at room temperature for PANI/Ni_0.5Zn_0.5Fe₂O₄ composites in the 50 Hz–5 MHz frequency range. PANI/Ni_0.5Zn_0.5Fe₂O₄ composites were demonstrated as a promising functional material for the absorbing of electromagnetic waves at low frequencies because of a large amount of dipole polarizations in the polymer backbone and at the interfaces of the Ni–Zn ferrite particles and PANI matrix.     

A novel approach for preparation of Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Tb nanoparticles by sol-gel-microwave heating

Zn₂SiO₄:Tb nanoparticles were prepared by sol-gel-microwave heating for the first time. X-ray powder diffraction (XRD) analysis confirmed the formation of Zn₂SiO₄ in willemite structure. Field-emission scanning electron microscopy showed a narrow size distribution, small size (40–50 nm) and spherical shape of the particles. Energy dispersive spectroscopy result indicated that the ratio of Tb³⁺/Zn²⁺ was in agreement with that of the feed. Photoluminescence measurement indicated that the phosphor emitted strong green light centered at 545 nm under UV light excitation. The excitation spectra confirmed the energy transfer from the host material to the Tb³⁺ ions. This is in favor of the effective green emission of Zn₂SiO₄:Tb nanoparticles.     

Phase transition and electrical properties of gallium- and indium-doped Bi<Subscript>10</Subscript>Ti<Subscript>3</Subscript>W<Subscript>3</Subscript>O<Subscript>30</Subscript>

Polycrystalline samples of gallium- and indium-doped Bi₁₀Ti₃W₃O₃₀ (mixed-layer Aurivillius phase with the Ti⁴⁺ and W⁶⁺ distributed at random over the perovskite-like slabs) have been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. Doping with both In³⁺ and Ga³⁺ yields limited solid solutions and shifts the ferroelectric phase transition to lower temperatures. The heterovalent substitutions of In³⁺ and Ga³⁺ for Ti⁴⁺ and W⁶⁺ increase the oxygen vacancy concentration and, accordingly, the conductivity of the material relative to the undoped compound.     

Local amorphization of atomic structure in Mg<Subscript>0.54</Subscript>Zn<Subscript>0.46</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The structure of Mg_0.54Zn_0.46Fe₂O₄ ferrites has been studied using x-ray diffraction techniques. It is established that high-temperature annealing (T = 1280°C, τ = 0.5–8.0 h) leads to a change in the crystal structure of samples, which is accompanied by their local amorphization.     

Phase Equilibria in the Tl<Subscript>2</Subscript>S-Tl<Subscript>2</Subscript>Te-Tl<Subscript>9</Subscript>BiTe<Subscript>6</Subscript>-TlBiS<Subscript>2</Subscript> system

The phase equilibria in the Tl₂S-Tl₂Te-Tl₉BiTe₆-TlBiS₂ system have been studied by differential thermal analysis and x-ray diffraction. The results have been used to construct the T-x phase diagram along the Tl₂S-Tl₉BiTe₆ ([TlBi_0.333S_0.5Te_0.5]) and TlBiS₂-Tl₂Te(Tl₉BiTe₆) joins, the 500-K section of the phase diagram of the Tl₂S-Tl₂Te-Tl₉BiTe₆-TlBiS₂ system, and its liquidus diagram. The invariant and univariant phase equilibria involved have been identified. The system has been shown to contain wide regions of Tl₂Te-and Tl₉BiTe₆-based quaternary solid solutions.     

Magnetic properties of (Co,Al) co-doped SnO<Subscript>2</Subscript> nanoparticles

The desired size of pure SnO₂ and Co (1, 3, 5 mol%) with constant 5 mol% of Al co-doped into SnO₂ nanoparticles are synthesized by chemical co-precipitation method. The raw materials used in synthesis are SnCl₂.2H₂O, AlCl₃, Co (C₂H₃O₂).4H₂O, aqueous NH₄OH and Polyethyleneglycol (PEG) from AR grade. The XRD pattern of pure and co-doped samples confirm the formation of tetragonal rutile phase of SnO₂ nanoparticles with average particle size 25 and 20 nm respectively. Micrographs of scanning electron microscope (SEM) for pure and (Co, Al) co-doped into SnO₂ show that the prepared nanoparticles are agglomerate and spherical in shape. The EDAX spectra of prepared nanoparticles indicate the presence of Co²⁺, Al³⁺, Sn⁴⁺ and O²⁺ and also confirm stoichiometric proportions of raw material in the formation of SnO₂. Transmission electron microscope (TEM) reveals that the surface morphology of pure and co-doped samples are spherical, and average size of particles is ~20 nm. Magnetization measurements from M-H curves of VSM show that the ferromagnetism at low concentration of Co and at higher concentration of Co shows weak ferromagnetism due to super exchange coupling among neighboring ions. The bound magnetic polarons model supports the observed ferromagnetic behavior.     

Piezoelectric and magnetic properties of PZT-(Ni<Subscript>0.284</Subscript>Zn<Subscript>0.549</Subscript>Cu<Subscript>0.183</Subscript>)Fe<Subscript>1.984</Subscript>O<Subscript>4</Subscript> composites

The piezoelectric/piezomagnetic composite, PZT/Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄, was fabricated by the mixed oxide method. The phase assemblage, piezoelectric strain constant and saturation magnetization were investigated. The results indicate that the PZT phase is compatible with Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄ phase, and dense diphasic ceramic composites were obtained. It is found that piezoelectric strain constant decreases exponentially as the amount of doped piezomagnetic materials in the composite increases. Correspondingly, saturation magnetization of the composite also decreases with the increasing weight fraction of piezoelectric materials. Three reasons cause the results. First, the grain growth of piezomagnetic phase at the co-sintering temperature reduces grain size and continuity of the piezoelectric phase. Second, the pore size and porosity in composite increase dramatically with increasing amount of piezomagnetic phase. Third, the low resistivity of the composite prevents the poling process and reduces the piezoelectric strain constant. The tailoring of microstructure to achieve a high performance piezoelectric/piezomagnetic composite is proposed based on the analysis.     

Synthesis,microstructure, and gas-sensing properties of SnO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> nanocomposites

SnO₂/MoO₃ nanocomposites are synthesized in a broad composition range through chemical precipitation from solution, and their phase composition and microstructure are investigated by x-ray diffraction. The gas sensitivity of the nanocomposites to lower alcohols (C_nH_{2n + 1} OH, n=1–4) is studied by in situ conductance measurements. The results are interpreted in terms of the acid-base properties of the nanocomposite surface.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 442–449.Original Russian Text Copyright © 2005 by Makeeva, Rumyantseva, Gaskov.     

Elastic properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The complete elastic modulus matrix of Li₂Zn₂(MoO₄)₃ single crystals has been measured for the first time. The sound velocity has been measured in different directions of the crystals by a pulse-phase method. The measurement results have been used to calculate elastic moduli. The sound velocity has been calculated in the three main crystallographic planes of the crystals.     

Co-precipitation method for the preparation of ferroelectric CaBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript>

A simple co-precipitation technique has been successfully applied for the preparation of pure single phase CaBi₄Ti₄O₁₅ (CBT) powders. Ammonium oxalate and ammonium hydroxide were used to precipitate Ca²⁺, Bi³⁺ and Ti⁴⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 600 C and pure CBT phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 400. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Electrical and thermodynamic properties of Cs<Subscript>0.97</Subscript> Rb<Subscript>0.03</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript>

The transport properties of Cs_0.97Rb_0.03H₂PO₄ have been studied using polycrystalline samples and single crystals. The mixed salt is isostructural with cesium dihydrogen phosphate and has slightly smaller unitcell parameters. The cation substitution increases the low-temperature ionic conductivity of the material by about two orders of magnitude but has an insignificant effect on the conductivity of the high-temperature phase. The low-temperature conductivity of single-crystal samples exhibits significant anisotropy, with σ _a < σ _b±c . The conductivity of the polycrystalline material is close to σ _b±c . The substitution reduces the temperature of the superionic phase transition by 20°C and enhances the thermal stability of the high-temperature phase at low humidity (1 mol % H₂O).