Crystallization and visible-near-infrared luminescence of Bi-doped gehlenite glass

Gehlenite glass microspheres, doped with a different concentration of Bi3+ ions (0.5, 1, 3 mol%), were prepared by a combination of solid-state reaction followed by flame synthesis. The prepared glass microspheres were characterized from the point of view of surface morphology, phase composition, thermal and photoluminescence (PL) properties by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and PL spectroscopy. The closer inspection of glass microsphere surface by SEM confirmed a smooth surface. This was further verified by XRD. The basic thermal characteristics of prepared glasses, i.e. Tg (glass transition temperature), Tx (onset of crystallization peak temperature), Tf (temperature of the inflection point of the crystallization peak) and Tp (maximum of crystallization peak temperature), were estimated from the DSC records. High-temperature XRD experiments in the temperature interval range 600–1100°C were also performed. The PL emission properties of prepared glasses and their polycrystalline analogues (glass crystallized at 1000°C for 10 h) were studied in the visible and near-infrared (NIR) spectral range. When excited at 300 nm, the glasses, as well as their polycrystalline analogues, exhibit broad emission in the visible spectral range from 350 to 650 nm centred at about 410–450 nm, corresponding to Bi3+ luminescence centres. The emission intensity of polycrystalline samples was found to be at least 30 times higher than the emission of their glass analogues. In addition, a weak emission band was observed around 775 nm under 300 nm excitation. This band was attributed to the presence of a minor amount of Bi2+ species in prepared samples. In the NIR spectral range, the broad band emission was observed in the spectral range of 1200–1600 nm with the maxima at 1350 nm. The chemistry of Bi and its oxidation state equilibrium in glasses and polycrystalline matrices is discussed in detail

Magnetic properties of yttrium iron garnet polycrystalline material prepared by spray-drying synthesis

The yttrium iron garnet polycrystalline powder was prepared by spry-drying synthesis from nitrates solution. The calcined powder was pressed into pellets and sintered at various temperatures for 2 hours. Prepared samples were characterized by XRD analysis and magnetic properties were measured. The magnetic moment of 4.3 µB and saturation magnetization of 24 Am2kg-1were observed for sample sintered at 1000 °C

Magnetic Properties of Synthetic Gehlenite Glass Microspheres

In the paper, gehlenite amorphous microspheres were prepared by the flame synthesis of a powder precursor. In the first step, the precursor was prepared from a stoichiometric mixture of CaCO₃, Al₂O₃ and SiO₂ by a standard solid-state reaction method. Next, the precursor was sprayed into a CH₄-O₂ flame with the temperature of around 2200°C and molten droplets of synthetic gehlenite were rapidly cooled by distilled water. Structural and detailed magnetic properties were studied by the optical microscopy, X-ray diffraction and QD SQUID magnetometer. The gehlenite microspheres show a complex magnetic behaviour that is a function of the temperature and the magnetic field, e.g. diamagnetism and paramagnetism at 300 K and 2 K, respectively

Preliminary study of thermal properties of Al₂O₃-Yb₂O₃ glass microspheres

Binary ytterbium-aluminate glass microspheres with eutectic (79.4 mol. % Al2O3, 20.6 mol. % Yb2O3) composition were prepared by flame synthesis in methan-oxygen flame. The starting powder was prepared by sol-gel method in order to obtain homogenous glass particles with a narrow interval of particle size distribution. Prepared microspheres were studied by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and differential thermal analysis (DTA). According to the XRD, small portion of YbAG, α-Al2O3 and non-identified phase were present in glass microspheres after flame synthesis. From DTA records, temperatures of onset of crystallization (Tc) and temperature of maxima of the exothermic crystallization peak (Tx) were determined. High temperature X-ray diffraction analysis (HT-XRD) in temperature range 750-1200 °C with 2h and 4h isothermal holding time at temperatures 933 and 1044 °C was performed for preliminary study of thermal behaviour of prepared system

Thermal behaviour of yttrium aluminate glasses studied by DSC, high-temperature X-ray diffraction, SEM and SEM–EDS

DSC, SEM-EDS, XRD and high-temperature XRD analysis was used to study thermal and crystallization behaviour of yttrium aluminate glasses prepared in the form of microspheres. The glasses YA-E (eutectic composition from the pseudo-binary system Al2O3-Y3Al5O12) and YA-G (a composition identical to the stoichiometric Y3Al5O12 (YAG) phase) were prepared by combination of the Pechini method with flame synthesis. The resulting microspheres were largely amorphous, but contained traces of yttrium-aluminium garnet as the main crystalline phase embedded in the yttrium aluminate glass matrix. Crystallization of the YAG phase was observed as the dominant exothermic process on DSC curves. From the DSC records, the basic thermal characteristics of the matrix glass, i.e. T (g) (glass transition temperature), T (x) (onset of crystallization peak temperature), T (f) (temperature of the inflection point of the crystallization peak) and T (p) (maximum of crystallization peak temperature), were determined. HT XRD experiments in the temperature interval 750-1200 A degrees C and isothermal HT XRD experiments at 932, 998 and 1200 A degrees C with 6-h holding time were also performed. Crystallization experiments at lower temperatures 932 A degrees C (YA-E) and 915 A degrees C (YA-G) were conducted to study phase development in a low-temperature region. Crystallization experiments at higher temperatures (1000, 1300 and 1500 A degrees C) with maximum holding time of 6 h were performed to study crystallization of alpha-Al2O3 in the eutectic system. The SEM and SEM-EDS examination of polished cross sections of crystallized microspheres revealed slow volume crystallization of the YAG phase in the AY-E glass. Eventually, polycrystalline microspheres with fine-grained microstructure were prepared after 6-h treatment at 1500 A degrees C