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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:21 |
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Conference: Bucharest University Faculty of Physics 2005 Meeting
Section: Optics, Spectroscopy, Plasma and Lasers
Title:
Synthesis by a citrate sol-gel method and characterization of Eu3+ doped yttrium aluminum garnet nanocrystals
Authors:
A. M. Chinie, A. Stefan, S. Georgescu
Affiliation:
National Institute for Laser, Plasma and Radiation Physics,
Bucharest-Magurele, 077125, P. O. Box. MG-36 Lab 21
E-mail
anachinie@yahoo.com
Keywords:
nanocrystals, sol-gel method, Eu
Abstract:
Yttrium aluminum garnet (YAG) is an excellent material with stable physical and chemical properties, high hardness and good thermal conductivity. YAG crystallizes in the cubic form and exhibits outstanding properties when doped with a lanthanide or transition elements.
Since the solid-state synthesis of YAG from aluminum and yttrium oxides requires high sintering temperatures (above 16000C), it is difficult to control both the homogeneity and purity of YAG powders in such synthesis conditions. Recently, high purity and well-controlled nanocrystalline YAG powders were obtained with various sol-gel methods. In this paper we employed a nitrate-citrate sol-gel method which has the advantages of both wet-chemical and solid-state synthesis methods, such as low temperature synthesis (~9000C), well-dispersed nanoparticles, inexpensive precursors, ease of preparation. We have analyzed the formation process of synthesized powders and we have investigated optical properties of Eu3+ doped samples.
In order to dope the YAG nanocrystals with Eu3+, aqueous solutions of Y(NO3)35H2O 1.93M, Al(NO3)39H2O, and Eu(NO3)35H2O 1.93M are mixed in a molar ratio Y:Eu:Al of 2.97:0.03:5 (Y2.97Eu0.03Al5O12 ). The mixture was added to a citric acid solution (C6H8O7H2O) 2M, in molar ratio citric acid: nitrates of 3:1. The mixture was evaporated at 80C until a transparent viscous gel was obtained. The gel was decomposed at 6000C for 6h obtaining a black powder, which then was calcinated at ~9000C for 6 h in air, achieving this way a white powder.
Powder X-Ray diffraction (XRD) patterns were recorded, using a TUR M 62 X-Ray diffractometer (Co-K radiation) after each thermal treatment. The fluorescence spectra were excited at room temperature with a Xenon lamp and suitable filters.
For thermal treatments at temperatures up to 9000C both XRD and optical spectroscopy show the presence of an amorphous phase. For higher temperatures, an unique garnet phase is indicated by XRD and by the fluorescence spectra
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