Publication: Synthesis of Cerium-Activated Yttrium Aluminate Based Fine Phosphors by an Aerosol Route
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2012-06
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Wiley
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Abstract
Polycrystalline fine powders of yttrium aluminate doped with Ce³⁺ were synthesised by spray pyrolysis of a polymeric pre-cursor, which was obtained by dissolving the corresponding nitrates in a solution of ethylenediaminetetraacetic acid (EDTA) in ethylene glycol (EG). Aerosol decomposition was performed at 550 °C followed by an additional thermal treat-ment (900–1100 °C). The yield of either a single yttrium alu-minium perovskite (YAP) phase or a single yttrium alumin-ium garnet (YAG) phase was investigated as a function of the predefined yttrium/aluminium ratio, the cerium doping concentration, the processing temperature, and the thermal-treatment regime, which included the variation of the heat-ing and cooling rates (dT/dt), the residence time (τ), and the atmosphere. Changes in the composition and structure of the precursor during thermal decomposition were investigated by thermogravimetric and differential thermal analysis (TGA/DTA) and FTIR spectroscopy. The particle morphology and structure were analysed by a combination of scanning electron microscopy and energy-dispersive X-ray spec-troscopy (SEM/EDS) and by highresolution transmission electron microscopy (HR-TEM). The structural refinement was based on the phase identification performed by X-ray powder diffraction (XRPD). The emission spectra were re-corded within the range 325–800 nm by applying excitation wavelengths of 297 (YAP) and 450 nm (YAG). The employed synthesis conditions assured the formation of spherical, non-agglomerated particles with well-developed surfaces and diameters between 200 and 800 nm. For a predefined Y/Al ratio of 1:1, lower processing temperatures combined with longer heat treatments under stationary conditions resulted in a multiphase system, composed of YAP, YAG, and mono-clinic yttrium aluminate (YAM) phases. However, a short heat treatment with a high heating rate (200 °C/min) at higher temperatures results in the formation of a kinetically favoured pure YAP hexagonal phase. On the other hand, for a predefined Y/Al ratio of 3:5, the generation of a thermody-namically favoured pure YAG phase has been confirmed, re-gardless of the applied heat-treatment conditions. Although incomplete, Ce³⁺ introduction into the host matrix has been detected by XRPD and luminescence measurements.
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Yttrium aluminates, Nano-particles, Luminescence, Polymerization, Spray pyrolysis
Bibliographic citation
European Journal of Inorganic Chemistry (2012). 2012(16), 2716-2724.