Effects of UV irradiation on Ce_1-xPr_xO₂ nanocrystals

Wei Min Tu¹, Peng-Chun Wang¹, Tai-Sing Wu², and Yun-Liang Soo<sup>1,2



1</sup>Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

²National Synchrotron Radiation Research Center, Hsinchu, Taiwan



We have investigated the effects of ultra-violet (UV) irradiation on the structures and electronic properties of CeO₂, Pr₆O₁₁, and Ce_1-xPr_xO₂ nanocrystals with x=0.1~0.7 prepared using a polyol method. The crystal structure, microstructure, bandgap, cation valence states of the samples before and after UV irradiation were determined by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflectance spectra, and x-ray absorption near edge structure (XANES) measurements, respectively. After UV irradiation, the bandgaps of the CeO₂ and Ce_1-xPr_xO₂ samples were slightly narrowed, as opposed to the widened Pr₆O₁₁ bandgap. Also, the reduction of Ce⁴⁺ ions to Ce³⁺ in CeO₂ and the reduction of Pr⁴⁺ ions to Pr³⁺ in Pr₆O₁₁ due to UV irradiation were observed. While substantial reduction of Pr⁴⁺ occurred, the reduction of Ce⁴⁺ was largely suppressed in the Ce₁₋ₓPrₓO₂ sample after UV irradiation. Our results demonstrate that it is easier to create oxygen vacancies around Pr than around Ce, while the bandgap variation follows the trends of Ce oxides rather than Pr oxides under UV irradiation in Ce₁₋ₓPrₓO₂ nanocrystals. Variations in catalyst activity due to UV irradiation in Ce₁₋ₓPrₓO₂ nanocrystals for photocatalysis applications will also be discussed.