Synthesis and luminescent properties of strontium aluminates activated with bismuth ions

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A series of derivatives of 2-(fur-2-yl)-5-phenyloxazole with various substituents in the 5-position of the furan ring and furan-containing analogs of 1,4-bis(5-phenyloxazol-2-yl)benzene are synthesized. Their spectral-luminescent properties are investigated.

For the first time, the Sr2La8 – xTmx(GeO4)6O2 (x = 0.1–1.0) solid solution with the apatite structure were synthesized by the solid-phase method, and their spectral–luminescence properties were studied. The prospects of using these compounds as phosphors in the visible and short-wave infrared ranges were demonstrated. The luminescence of Sr2La8 – xTmx(GeO4)6O2 germanates, which occurs under ultraviolet radiation, is characterized by the high purity of blue color; the chromaticity coordinates are close to commercially available phosphors. The Sr2La8 – xTmx(GeO4)6O2 compounds efficiently convert 808 nm laser radiation into a series of emission lines in the 1.3–2.2 μm spectral range, caused by sequential 3H4 → 3F4 and 3F4 → 3H6 transitions in Tm3+ ions. Germanate Sr2La7.6Tm0.4(GeO4)6O2 with a maximum emission intensity in the short-wave infrared region shows high thermal stability of luminescence in the 30–220°C range.

As the information era continues to advance at a rapid pace, M-type strontium ferrite and other magnetic materials are finding more and more traditional uses. Numerous industries rely on it as a permanent magnet material because of its inexpensive cost, ease of preparation, and outstanding overall performance in areas including electronics, national defense, and communication. In this paper, we investigate some the magnetoelectric coupling properties at room temperature by solid phase method and sol-gel method. The phase structure was determined using an X-ray diffractometer, and the samples were all single-phase polycrystalline with a spatial group of P63/mmc. Observing the surface morphology using field emission scanning electron microscopy, it was found that the composition distribution of the samples prepared by solid-phase method was uneven and there was a "scandium rich phase". The samples prepared by the sol gel method have uniform composition distribution, hexagonal grain shape, and grain size of about 3-5 μ M. The magnetic properties of the samples prepared by the sol gel method and the solid phase method were studied, respectively. The results showed that the phase transition occurred in the solid phase method at about 250K, and the hysteresis loop at room temperature did not show the magnetoelectric coupling behavior. The magnetic phase transition of the sample prepared by the sol gel method occurred near 330K. Combined with the research on the hysteresis loops of the temperature above and below this phase transition point, it shows that this phase transition corresponds to the change of the ferromagnetic to the conical magnetic structure. The similar relationship between magnetic capacitance and magnetization intensity with magnetic field indicates that this conical magnetic structure can induce ferroelectric polarization, which can be understood based on the inverse Dzyaloshinskii-Moriya model.

A ratiometric optical thermometer based on Bi3+ and Mn4+ co-doped La2MgGeO6 phosphor with high sensitivity and signal discriminability

Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to remarkable advances in photovoltaic devices. However, due to environmental and stability concerns around the use of lead, research into lead-free perovskite structures has been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH4)3Bi2I9, is prepared from solution and the structure solved by single crystal X-ray diffraction. The band gap, which is estimated to be 2.04 eV using UV-visible spectroscopy, is lower than that of CH3NH3PbBr3. The energy-minimized structure obtained from first principles calculations is in excellent agreement with the X-ray results and establishes the locations of the hydrogen atoms. The calculations also point to a significant lone pair effect on the bismuth ion. Single crystal and powder conductivity measurements are performed to examine the potential application of (NH4)3Bi2I9 as an alternative to the lead containing perovskites.

ABSTRACTThe discovery of rare earth based phosphors in 1960s started a new era of luminescence. In comparison with sulfide‐based phosphors, strontium aluminates received worldwide acceptance because of their chemical stability and good luminescent properties. The SrAlxOy:Eu2+,Dy3+ phosphors excited by UV or visible light emit phosphorescence in the blue‐green region after the excitation source has been removed, and the phosphorescence last for more than 15 h. The major disadvantage of SrAlxOy:Eu2+,Dy3+ phosphors is that they are prone to hydrolysis and their luminescent properties gradually deteriorate. The dispersion of these phosphors in a waterproof polymer matrix is an alternative method reported for retaining their luminescent properties. The review extensively deals with strontium aluminate based luminescent materials, the mechanism of luminescence, their synthesis techniques, and different mixing procedures to prepare polymer/strontium aluminate composites. Different methods to improve the dispersion of the strontium aluminate in the polymer matrix are also outlined.

The alumino‐silicate series (Al4+2xSi2−2xO10‐x, x = 0–1), is an important class of structural ceramics with many applications. Except for the end member (x = 0), which is the crystalline phase sillimanite, the reported crystal structures of the other phases, called mullites, all have partially occupied sites which makes any theoretical calculation a formidable task. In this article, we describe a systematic and detailed theoretical investigation of the structures and properties of the phases in this series. We constructed stoichiometric supercell models for the four well‐known mullite phases 3Al2O3·2SiO2, 2Al2O3·SiO2, 4Al2O3·SiO2, 9Al2O3·SiO2, corresponding to x = 0.25, 0.40, 0.67, and 0.842. The construction of the models began with experimentally reported crystal structures followed by systematic removal of selected atoms at the partially occupied sites to maintain charge neutrality. A large number of models were built for each phase and fully relaxed to high accuracy using the Vienna ab initio simulation package program. The model with the lowest total energy for a given x was chosen as the representative structure for that phase. Together with sillimanite (x = 0) and the silica free ι‐Al2O3 (x = 1), this series' electronic structure and mechanical properties were studied via first‐principles calculations. Their elastic coefficients and mechanical properties (bulk modulus, shear modulus, Young's modulus, and Poisson's ratio) were evaluated. The electronic structure, effective charges, bonding, and optical properties of these mullite phases were calculated using the orthogonalized linear combination of atomic orbitals method. These first‐principles results provide the basis for an explanation of the experimentally observed structure and properties of mullite phases and their trends with x at the fundamental level.

Studies on preparation and properties of low temperature phase of MnBi prepared by electrodeposition

Influence of microwave process on photoluminescence of europium-doped strontium aluminate phosphor prepared by a novel sol–gel-microwave process

In this paper, europium-doped strontium aluminate (SrAl2O4:Eu(2+)) phosphors were synthesized using a combustion method with urea as a fuel at 600°C. The phase structure, particle size, surface morphology and elemental analysis were studied using X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectra. The EDX and FTIR spectra confirm the elements present in the SrAl2O4:Eu(2+) phosphor. The optical properties of SrAl2O4:Eu(2+) phosphors were investigated by photoluminescence (PL) and mechanoluminescence (ML). The excitation and emission spectra showed a broad band with peaks at 337 and 515 nm, respectively. The ML intensities of SrAl2O4:Eu(2+) phosphor increased proportionally with the increase in the height of the mechanical load, which suggests that this phosphor could be used in stress sensors. The CIE colour chromaticity diagram and ML spectra confirm that the SrAl2O4:Eu(2+) phosphor emitted green coloured light.

Despite the potential application of uranyl‐organic coordination polymers (UOCPs) in detecting metal cations and radiation rays, their luminescence properties have not been sufficiently studied at the molecular level. Herein, we synthesized a series of UOCPs (UOCP1–9) with new construction based on bipyridinium salts and diverse auxiliary ligands. The physicochemical properties of the complexes with high purity were systematically characterized, especially the luminescence spectra. A deep theoretical investigation was conducted to illustrate the relation between uranyl coordination and the luminescence spectral property. The results show that the influence of ligand type on the uranyl luminescent spectral properties increases in the order of hydroxide>oxalate>aromatic carboxylate, which can be attributed to the magnitude of orbital interaction between uranyl and ligand. This work helps to profoundly understand uranyl optical properties and electronic structure at the molecular level, providing important hints for recognizing the nature of luminescent spectral features of uranyl‐containing materials, as well as the fundamental chemistry of actinide elements.

Although past studies have shown a competitive relationship between bismuth ion (Bi 3+ ) and rare earth ions in potassium sodium niobate {(K, Na)NbO 3 , KNN}‐based ceramics, a comprehensive investigation of this competition has been relatively scarce. Herein, we conducted an in‐depth exploration of this competition by substituting Bi 3+ with praseodymium ions (Pr 3+ ) in KNN‐based ceramics possessing high piezoelectric properties. The substitution of Bi 3+ with Pr 3+ results in a decrease in the extent of multi‐phase coexistence at room temperature, an increase in domain size and grain size, and the enhancement of ferroelectricity. However, it also leads to a deterioration in piezoelectricity. Through a combination of experimental findings and first‐principles calculations, we analyzed the alterations in phase structure, ferroelectric domains, and electrical properties, attributing these changes to the competitive nature of Bi‐O and Pr‐O bonds with their distinct ionic/covalent characteristics. Consequently, this study not only unveils the underlying physical mechanism behind the competition between Bi 3+ and Pr 3+ ions in KNN‐based piezoceramics but also presents a novel approach to tailor the phase transition temperature, thereby facilitating the overall performance improvement of KNN‐based ceramics.

In this work strontium aluminate doped with trivalent europium ion was prepared by the method of evaporation of poly vinyl alcohol and their luminescence, structural and thermal properties were investigated. The samples were characterized by thermal differential and thermogravimetry analysis, structural analysis was performed by X-ray diffraction and Fourier transform infrared spectroscopy and luminescence by fluorescence emission spectroscopy. The thermal analysis of aluminate samples showed two mass losses accompanied by endothermic and exothermic processes during the calcination process, not depending on the time employed in calcination. The infrared spectra exhibited characteristic bands of the metals involved in the synthesis of the material demonstrating the formation of strontium aluminate. The diffratogram patterns showed the formation of cubic phase Sr3Al2O6. The fluorescence characterization showed two emission bands attributed to matrix and europium excited states and it was observed that as the calcination time and temperature were increased, the emission of europium in the material was less efficient.

Two new banana-shaped mesogens have been prepared and their mesophases have been studied. As indicated by calorimetry and polarizing microscopy both compounds exhibit two smectic mesophases. The structure of these phases have been studied by X-ray methods and NMR measurements. The electrooptical properties are discussed on the base of the structural data.