2O₄: Correlation of X-ray Diffraction, M?ssbauer Spectroscopy, X-ray Absorption Spectroscopy, and Photoluminescence Investigations]]>

摘要

Powder samples of pure BaAl_(2)O_(4) and doped with 4.9 atom % Eu in relation to Ba were prepared by a hydrothermal route. The samples were characterized by X-ray diffraction, ~(151)Eu M?ssbauer spectroscopy, synchrotron-based X-ray absorption spectroscopy at the Ba L_(3)- and Eu L_(3)-edges, and photoluminescence measurements. Diffraction lines were broadened, indicating that the samples were nanocrystallline. The samples possessed a hexagonal crystal structure, space group P 6_(3). ~(151)Eu M?ssbauer spectroscopy revealed the presence of Eu in the 3+ oxidation state. The same information on the Eu oxidation state was also obtained by the Eu L_(3)-edge X-ray absorption near-edge structure of the doped sample. Extended X-ray absorption fine structure showed an Eu~(3+) ion substituted for Ba~(2+) on the Ba2 site in the BaAl_(2)O_(4) host structure, with charge compensation by an interstitial O in the vicinity of the Ba2 site. That was confirmed by a Rietveld structure refinement for the Eu-doped BaAl_(2)O_(4) sample. Analysis of the diffraction line broadening for the prepared samples was performed simultaneously with the structure refinement. Both the dopant Eu~(3+) and the interstitial O acted as defects in the host BaAl_(2)O_(4) lattice, which increased the lattice strain from 0.02% for pure BaAl_(2)O_(4) to 0.17% for the Eu-doped sample. Crystallite sizes in the samples increased with Eu doping from 32 nm for pure BaAl_(2)O_(4) to 36 nm for Eu-doped BaAl_(2)O_(4). This could likely be related to the increase in the diffusion rate of the cations in the sample when a part of the Ba~(2+) cation content was exchanged with smaller Eu~(3+) cations. The Eu-doped BaAl_(2)O_(4) sample exhibited red photoluminescence under excitation with λ_(exc) = 308 nm. The observed emission spectrum indicated that Eu~(3+) ions occupied the Ba site with lower symmetry in the doped sample.