Temperature and ionic size dependence of the properties of ceria based optionic thin films

Thin films of CexLn1−xOy (Ln=La, Nd, Gd, and Yb and x=0.85) were deposited by an inorganic sol–gel technique and the dependence of the refractive index, optical absorption and absorption edge of these films on post deposition annealing temperature has been studied. It has been found that the refractive index of all the films increases with increase in temperature up to 1050°C. Significantly, the value of refractive index obtained is dopant ionic size dependent. After annealing at 1050°C for 1 h, the undoped ceria films showed the highest value of 2.13 at 800 nm while the highest value obtained in La doped films was 1.97 at the same wavelength and temperature. The values for Nd, Gd and Yb were 1.94, 1.97 and 1.85, respectively at the same wavelength and temperature. Annealing at 1050°C for 16 h increased the refractive index further but reduced the transmittance in the short wavelength region (<500 nm) for all the materials. It has also been found that both the optical absorption and absorption edge are temperature dependent.