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Three types of precursors were prepared using the wet-chemical synthesis route, starting from yttrium-europium-aluminum nitrate solution and different precipitating agents (urea, oxalic acid, and ammonium carbonate). The precursors were fired at 1200 °C in nitrogen atmosphere in order to obtain europium-doped yttrium aluminate YAlO:Eu phosphor with garnet structure (YAG:Eu). The processes involved in the thermal decomposition of precursors and their composition were put in evidence using thermal analysis (TG-DTA) and FT-IR spectroscopy. The GA-DTA curves possess typical features for basic-oxalate, -nitrate, and -carbonates as formed with oxalic acid, urea, and ammonium carbonate, respectively. Correlation between the thermal decomposition steps, mass loss, and composition of gases evolved during the thermal treatment was established using TG-DTA-FT-IR coupling. It was found that the different composition of precursors reflects on the luminescent characteristics of the corresponding phosphors. Urea and ammonium carbonate lead to the formation of YAG type phosphors, with garnet structure and specific red emission. As for the oxalic acid, this precipitating agent generates a non-homogeneous powder that contains yttrium oxide as impurity phase. This phosphor is a mixture of YO:Eu, YAlO:Eu, and YAlO:Eu that explain the relative higher emission intensity. [ABSTRACT FROM AUTHOR]

The thermal behaviour of three ester derivatives of p- tert-butyl calix[ n]arene ( n = 4, 6 and 8) in comparison with the parent calixarene was investigated by means of the thermogravimetric (TG) and differential thermogravimetic (DTG) analysis and differential scanning calorimetry (DSC). The thermal stability domains, the composition of the pyrolysis products and the thermal effects, were determined on the basis of TG, DTG and DSC plots registered in nitrogen flow. Attempts to analyse the evolved gases by TG-FTIR coupling were also performed. It was demonstrated that the stability of the calix[ n]arene derivatives depends on both the size of the hydrophobic cavity and number of the substituting groups grafted on the calix[ n]arene skeleton. [ABSTRACT FROM AUTHOR]

Abstract: The laser synthesis of nanoparticles starting from liquid precursors is particularly suitable as synthesis technique for obtaining nanoparticles. In the present work the laser pyrolysis is performed in a novel setup where the liquid precursor is brought with the aid of an original evaporator system to temperatures in excess of the boiling point and is finally fed into the reactor under the form of heated vapors.The process occurs in the gas phase and ensures the avoidance of the condensation. The temperature control system allows for the maintaining of the overall system temperature below the decomposition temperature and above the boiling. Temperatures up to 500°C are assured for the mixed precursors. The control of the amount of the active substances is performed upstream, in the liquid phase. The set-up is able to offer safety conditions at the synthesis of substances with high toxicity. This experimental set-up was proposed in order to synthesize TiO2 nanoparticles from TTIP because its boiling temperature is relatively high (239°C grades). Different analytical techniques such as EDX, TEM, XRD and HRTEM were used in order to evaluate the structural characteristics of the produced nanopowders. [Copyright &y& Elsevier]

Nanocrystalline undoped and manganese doped zinc sulphide (ZnS) powders were prepared by microwave—assisted solvothermal decomposition of zinc-manganese diethyldithiocarbamate as single-source molecular precursor. The precursors are being obtained in aqueous solution, from sodium diethyldithiocarbamate and zinc-manganese acetate mixtures containing variable amounts of manganese. Complementary investigations such as: thermal analysis, X-ray diffraction, SEM and BET were used to characterize both the precursors and phosphors. After the solvothermal treatment, the specific surface area of the powders increases from 2.04 m 2 /g to 154.5 m 2 /g. Phosphor samples consist of small particles (∼12 nm) which present a high tendency to form spherical agglomerations. Photoluminescence spectra show a dominant yellow emission peak at 568 nm accompanied by several weaker peaks. In this paper, we discuss about the manganese incorporation effect in ZnS lattice concerning the morpho-structural and luminescent characteristics of the samples. [ABSTRACT FROM AUTHOR]