Local Structure of Nanocrystalline Lu₂O₃:Eu Studied by X-ray Absorption Spectroscopy

Abstract

Eu-doped nanocrystalline Lu2O3 with different particle sizes was prepared by combustion synthesis. The local structures around the rare-earth Lu and Eu ions were studied by using both Lu and Eu L3 edge X-ray absorption spectroscopy. According to the extended X-ray absorption fine structure (EXAFS) analysis, detailed local structure information such as coordination numbers, bonding length, and disorder has been obtained. The results showed that the samples with a particle size larger than 5 nm keep the cubic structure and the disorder increases with decreasing size. However, when the particle size is smaller than 5 nm, the existence of considerable amorphous components accounts for the rough interface and the obvious change of the local structure around the rare-earth ions. A new type of coordination environment around Eu was formed, and the most probable symmetry of the Eu3+ site was determined by combining the real-space self-consistent field full multiple scattering X-ray absorption near edge structure (XANES) calculation and the EXAFS result. The local structure information obtained from EXAFS and XANES was used to explain the size-dependent luminescent properties of the nanocrystalline Lu2O3:Eu. The decreasing intensity ratio between the host absorption band and the Eu3+−O2- charge-transfer state (CTS) band with decreasing particle size can be attributed to a larger disorder and more defects in the small sized samples, while the red shift of the CTS band in the smaller size particles can be ascribed to the longer Eu−O bond length and the higher coordination number.