Thin films of Ce-propionate (thickness below 20 nm) have been deposited by spin coating and pyrolysed into ceria at temperatures below 200 degrees C After 1 h of thermal treatment, no signature of the vibrational modes of Ce-propionate is detected by infrared spectroscopy, indicating that decomposition has been completed. The resulting ceria films are nanocrystalline as revealed by X-ray diffraction (average grain size of 2-2.5 nm) and confirmed by microscopy. They are transparent in the visible region and show the characteristic band gap absorption below 400 nm. A direct band gap energy of 3.50 +/- 0.05 eV has been deduced irrespective of the pyrolysis temperature (160, 180 and 200 degrees C). (C) 2011 Elsevier B.V. All rights reserved.