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Structural and Photoluminescence Study of Eu 3+ /TiO 2 Xerogels as a Function of the Temperature Using Optical Techniques
Author(s) -
Borlaf Mario,
Colomer María Teresa,
Moreno Rodrigo,
Andrés Alicia
Publication year - 2015
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.13299
Subject(s) - anatase , brookite , materials science , photoluminescence , calcination , analytical chemistry (journal) , raman spectroscopy , doping , rutile , grain size , mineralogy , chemical engineering , chemistry , photocatalysis , metallurgy , optics , biochemistry , physics , optoelectronics , chromatography , engineering , catalysis
Eu 3+ / TiO 2 xerogels have been obtained from colloidal sols by drying at room conditions. Anatase with traces of brookite phases are obtained from the synthesis and the stability of both with temperature is higher (from 400°C up to 800°C) when Eu 3+ is present. Raman phonons have been used to detect the different phases and follow the structural transitions. The observed changes with calcination temperature of anatase modes (E g,1, B 1g , 1 A g /B 1g,2, and E g,3 ) are found to be mainly related to the grain size. The anatase grain size increases more and at lower temperatures for undoped than for Eu 3+ ‐doped samples favoring the transition to rutile. The stability of the brookite phase is also influenced by the doping being higher in the doped xerogels (700°C) than in the undoped ones (400°C). No concentration quenching of the f – f Eu 3+ emission bands is observed up to 3% Eu 3+ at low temperatures but the maximum emission is found at lower temperatures for higher Eu 3+ content may be due to quenching related to Eu 3+ migration. The narrower f – f emission bands of the as‐prepared samples are consistent with the presence of Eu 3+ ions at the surface with a weak interaction with the TiO 2 nanoparticles. A diffusion process of Eu 3+ ions occurs during calcination from the surface to different positions of the anatase lattice close to the surface producing an inhomogeneous broadening. Finally, the formation of the pyrochlore phase Eu 2 Ti 2 O 7 is detected which explains the decrease on the emission efficiency and the increase of the Eu 3+ environment symmetry.