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Investigation of Eu-doping of barium aluminate (BaAl2O4) by XANES/EXAFS

Europium doped barium aluminate (BaAl2O4) is a luminescent material with emission in the red spectral range, and is widely used in the field of optical communication and electronics. Despite the actual use of Eu-doped barium aluminate in optoelectronic devices, structural investigations of this material have not yet been precisely performed so far. In this context, we have conducted X-ray absorption measurements at the absorption edges of the dopant and the host elements in order to elucidate the mechanism of incorporation of Eu in the BaAl2O4 host structure, as well as to understand the origin of the optical/luminescence properties of Eu-doped barium aluminate. Powder samples of undoped BaAl2O4 and ones of BaAl2O4 doped with 4, 6 and 8 at.% Eu (in relation to Ba) were prepared by a hydrothermal method and subsequently annealed at 1100 ºC for 4h. The Eu L3-edge X-ray absorption experiments on the doped samples were performed at DELTA beamline. Eu L3 XANES spectra of BaAl2O4 doped with 4, 6 and 8 at.% Eu were compared to those of Eu2O3 as a reference for Eu3+, and of a glass sample containing both Eu2+ and Eu3+ in approximately equal amounts. Precise analysis of these data showed that europium in the doped samples possesses a 3+ valence. The bond distance determined for the first Eu-O bond in the Eu-doped samples is substantially smaller compared to the Ba-O bond distance in pure BaAl2O4. However, it is also smaller compared to the Eu-O bond distance in pure Eu2O3. The large europium coordination number as determined from EXAFS data of the Eu-doped BaAl2O4 samples is not at all compatible with a tetrahedral or octahedral coordination symmetry with 4 or 6 nearest neighbors, but suggests the location of Eu3+ on the Ba2+ sites instead.

Barium aluminate; Eu doping; X-ray absorption spectroscopy; XANES; EXAFS

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