The optical band gap of Gd-doped CeO2 thin films as function of temperature and composition Original Research Article

Thin films of Ce1−xGdxO2−x/2 (x=0, 0.1, 0.2, 0.3) were prepared by Pulse Laser Deposition and characterized at room temperature by SEM, XRD and Raman spectroscopy. The coefficient of absorption of the 200 nm thin films was measured between room and liquid nitrogen temperatures. The direct and indirect optical band gaps were estimated using Tauc plots. Substitution of Ce for Gd was found to have a significant effect on the coefficient of absorption, although there is a weak band gap dependence upon temperature. This was attributed to the poor overlap of the 4f orbitals of the lanthanides in gadolinia-doped ceria. An expression for the direct and indirect optical band gap of each gadolinia-doped ceria as a function of temperature is given. As an example, for ceria the direct optical band gap is 3.66±0.008 eV −1.25±0.05×10−4 eV K−1.