Sol-gel synthesis and characterization of Eu+++/Y2O3 nanophosphors by an alkoxide precursor

Eu+++ doped Y2O3 nanoparticles have been synthesized by sol-gel process using an yttrium oxo-isopropoxide (Y5O(OPri)(13)) as precursor. X-ray diffraction and optical spectroscopy have been used to characterize these clusters. The as synthesized powder gave very broad peak in the X-ray diffraction suggesting amorphous or subnanocrystalline particles. The same pattern was found for the powder annealed at 300 degrees C for 5 h. However, annealing at temperatures between 400 and 800 degrees C gave well crystalline particles with average size between 17 and 43 nm. The ratio of intensities of D-5(0) -> F-7(1) and D-5(0) -> F-7(2) tranisitions in the europium emission spectrum has been used as structural probe to indicate the local environment around Eu+++ in the Y2O3 particles. It is concluded that in the samples annealed at temperatures below 800 degrees C europium is situated in the near octahedral holes of the Y2O3 lattice having high symmetry around them, while in the 800 degrees C heated sample the symmetry is comparatively less pronounced. This indicates that some of europium atoms are also at the nanoparticles surface. In comparison to other reports the local europium environment is much symmetrical even for our 800 degrees C annealed sample. (c) 2005 Elsevier B.V. All rights reserved.