UV and Visible Raman Studies of Oxygen Vacancies in Rare-Earth-Doped Ceria

Abstract

Surface properties of rare-earth (RE) doped ceria (RE = Sm, Gd, Pr, and Tb) were investigated by UV (325 nm) and visible (514, 633, and 785 nm) Raman spectroscopy, combined with UV−vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectra techniques. It was found that the optical absorption property of samples, the wavelength of detecting laser line, and the inhomogeneous distribution of the dopants significantly affected the obtained surface information, namely, the peak intensity and shape at ca. 460 and 570 cm⁻¹, as well as the observed oxygen vacancy concentration (A₅₇₀/A₄₆₀). The UV laser line detected the surface information of RE-doped ceria and disclosed the presence of many oxygen vacancies in the samples. The visible laser lines penetrated into the inner layer of the Sm- or Gd-doped CeO₂ and reflected the whole information of samples because of their weak absorptions of the visible laser. However, the Pr- or Tb-doped CeO₂ absorbed visible light strongly; thus, the laser can only determine the outer surface information of the sample.