Fluorine atoms have been reported as an impurity in cerium oxide; however, their influence on the electronic structure and chemical properties is not well understood yet. We show the changes in Ce 3d photoelectron spectra features induced by fluorine. We introduce a fitting procedure which allows to evaluate the concentration of fluorine in the cerium oxide layer. A correlation between the fluorine concentration and the characteristic Ce-F interaction doublets added to Ce 3d spectra fits is presented in this Letter. We studied also the interaction of the prepared layers with small doses of CO and O-2 gases at elevated temperatures. (C) 2015 Elsevier B.V. All rights reserved.