Modifications involved by acetylacetone in properties of sol-gel derived Y3Al5O12: Tb3+ - II: optical features

Tb3+-doped Y3Al5O12 powders have been synthesized from alkoxide precursors using, or not using, acetylacetone as a chemical modifier. The terbium oxidation state and local environment of amorphous and crystallized powders have been comparatively investigated by means of X-ray absorption near-edge structures (XANES) and extended X-ray absorption fine structure (EXAFS) while laser-induced luminescence was used to study their optical properties. Excitation and emission spectra have been recorded and a relative luminescence yield has been assessed upon 277 nm excitation. Whatever the sample, the terbium oxidation state remains +III and, for a similar heating treatment until 900 degrees C, its local environment appears to be better organized in powders modified by acetylacetone. Structural parameters obtained during XAS study are consistent with the YAG structure in which Tb atoms are in solid solution with Y ones. Besides, Tb3+ characteristic green luminescence has been recorded for all samples, even those amorphous. It has been evidenced that the use of acetylacetone leads to more efficient luminescent materials for calcination temperatures ranging from 400 degrees C to 900 degrees C upon 277 nm excitation. Discrepancies between optical properties will be discussed with regards to the terbium local environment and expected luminescence features.