Rare-Earth-Based Phosphor Particles Synthesis through Hydothermal and Spray Pyrolysed Routes

Poster presented at the 11th Conference of the Materials Research Society of Serbia - YUCOMAT 2009, Herceg Novi, Montenegro, August 31 – September 4, 200

Na0.76Fe0.79Ti1.21O4 N - the new type compound obtained from natural ilmenite sand under hydrotermal conditions

Poster presented at the COST Action 539- ELENA, 3rd Workshop, Bled, Slovenia, September 2, 200

Kinetics of nanocrystalline phase transformations in spray pyrolysed ZnO particles

The thermal behavior of ZnO powder obtained by ultrasonic spray pyrolysis of nitrate solution (c=0.8mol/dm3, D0=2.695µm, Tmax=6000C, FG=1.2dm3/min) was investigated using non-isothermal differential scanning calorimetry (DSC, heating rates 5, 10, 15, 20O/min). The exothermic heat effects at the temperature range from 350 to 5000C were linked to particles structural data obtained by XRD, SEM and TEM analysis. Produced particles are characterized by uniform submicronic size (D=800nm, BET=4.94m2/g), high phase purity and granular or circular “open” surface due to the presence of primary crystallites (d= 20nm). Observed structural changes during heating of this powder were attributed to simultaneous processes of nucleation and growth of primary crystallites inside the produced particles

Nanostructured Y2O3 Particles Doped with Europium Synthesized by Aerosol Route

Y2O3 doped with europium is a well known red phosphor material employed in modern high-resolution display devices such as plasma display panels (PDP) and field emission displays (FED). The incorporation of gadolinium in the yttria matrix may significantly contribute to the luminescent properties and x-ray absorption coefficient thus increasing the field of application in optoelectronic devices such as ceramic scintillators for computed tomography. In this work, the nanostructured particles of Y 2 O 3 doped with Eu 3+ were processed through the spray pyrolysis method. Synthesis was carried out with an ultrasonic aerosol device operating at 1.3 MHz in air atmosphere connected with a triple-zone tubular flow reactor (473-973-1173K). Particles were submitted t o post- thermal treatments at temperatures among 1273 and 1 573K for 12 hours in order to increase the crystallinity and uniform distribution of doped centers. Morphology, structure, crystallinity and chemical characteristics were studied by XRD, SEM-EDS, TEM-HRTEM and SAED. The particles obtained are spherical, having narrow size distributions, high compositional homogeneity and are in unagglomerated state. The effects of synthesis parameters were followed and discussed in terms of particle structure and morphology

Effect of processing parameters on structural and morphological Y2O3 :Yb3+/Ho3+ powders characteristics

Up-converting yttrium oxide powders doped with Yb3+ and co-doped with Ho3+ were\ud synthesized through hydrothermal processing at 200 °C/3 h. Reverse precipitation of the starting nitrates mixture is performed with the help of ammonium hydrogen carbonate (AHC) solution up to pH 7 or pH 9 prior to hydrothermal treatment. Morphological features of the as-prepared (asp)powders and rare earth oxides obtained after powders additional annealing at 1100 oC (3 and 12 h)are discussed based on X-ray powder diffractometry (XRPD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Structural refinement confirmed generation of the cubic bixbyte-structure (S.G. Ia-3) with non-uniform accomodation of dopants at C2 and S6 cationic sites. SEM revealed that the particles have plate-like or rod-like morphology in dependence of hydrothermal processing (pH). Due to the fact that are composed from nanograins (30-100 nm) they demonstrate prominent green luminescence centered at 550 nm after been excited with the infrared laser source (λ=978 nm)

The synthesis: Structure relationship in the ZnO-Cr2O3 system

In this work the development of the spinel phase in the ZnO-Cr2O3 system was discussed from the viewpoint of the synthesis-structure relationship. The nanostructure evolution in particles obtained either via solution-based (spray pyrolysis) or solid-state (mechanical activation) synthesis procedures were investigated by XRD analysis. A detailed structural analysis of the spinel phase lattice parameters, average primary crystallite sizes and micro strains were performed in accordance with a procedure based on the Koalariet-Xfit program. Due to the importance of spinel-phase cat ion distribution for chemical and physical properties, a study of the site occupation factors, i.e. changes in the stoichiometric, of ZnCr2O4 spinals was undertaken. The calculation based on atomistic methods for the description of both perfect and defect spinel ZnCr2O4 crystal lattices has been applied and the presence of individual structural defects was determined

HYBRID NEURAL LUMPED ELEMENT APPROACH IN INVERSE MODELING OF RF MEMS SWITCHES

RF MEMS switches have been efficiently exploited in various applications in communication systems. As the dimensions of the switch bridge influence the switch behaviour, during the design of a switch it is necessary to perform inverse modeling, i.e. to determine the bridge dimensions to ensure the desired switch characteristics, such as the resonant frequency. In this paper a novel inverse modeling approach based on combination of artificial neural networks and a lumped element circuit model has been considered. This approach allows determination of the bridge fingered part length for the given resonant frequency and the bridge solid part length, generating at the same time values of the elements of the switch lumped element model. Validity of the model is demonstrated by appropriate numerical examples

Urea-Assisted Self-Combustion Aerosol Synthesis of Y3Al5O12:Ce3+

Poster presented at the 10th Conference of the Materials Research Society of Serbia - YUCOMAT 2008, Herceg Novi, Crna Gora, 8-12. septembar 200

The Low Temperature Aerosol Synthesis of YAG:Ce3+ Nanostructures: comparative Study of XRPD Microstructural Parameters

Poster presented at the 8th Conference of Yugoslav Materials Research Society – YUCOMAT 2006, Herceg Novi, Montenegro, September 4-8, 200

Nax−y Hy Ti2−x Fex O4 ·nH2 O nanosheets with lepidocrocite-like layered structure synthesized by hydrothermal treatment of ilmenite sand

Nax−yHyTi2−xFexO4·nH2O nanosheets with lepidocrocite-like layered structure were produced through alkaline hydrothermal treatment at very low temperatures (130°C) from ilmenite sand. The crystal structure, morphology and optical properties were investigated by X-Ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive spectroscopy and UV-Vis spectroscopy. The product shows leaf-like nanosheet morphology with thickness <30 nm and lengths <1 µm. Three lepidocrocite-like titanates (Imm2 space group) with similar a and c lattice parameters but different interlayer distances (b/2) were identified. This appears to be the first preparation of lepidocrocite-like layered nanosheets by a simple, energy efficient (low temperature) and low cost (starting from mineral sand) procedure