Optical properties of copper modified sol-gel SiO2 thin films

Copper modified SiO2 thin films have been synthetized by sol-gel/dip coating process and annealed at 450 degrees C. The presence of crystallized CuO is only detected for the highest level of introduced Cu [Cu/(Cu+Si)=0.2]. UV-Visible absorption edge increases with the copper content in the film. Optical gap (E-g) and Urbach energy (E-u) extracted from the UV-Visible absorption curves evidence the large effect of the presence of copper species on silica optical properties. The decrease of the optical gap agrees with the lowering of the UV-Visible absorption peak energy calculated at the Time Dependent Density Functional Theory (TD-DFT) level for silica clusters without and with a copper atom. (C) 2012 Elsevier B.V. All rights reserved.