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 °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 (Eg) and Urbach energy (Eu) 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.

► Synthesis of transparent Cu modified SiO2 thin films ► Increase of absorption edge with Cu content ► Large modification of the SiO2 optical gap and Urbach energy due to the presence of Cu species ► TD-DFT simulation of UV–Visible spectra of SiO2 and SiO2–Cu based molecules ► The same trend on UV–Visible behavior is determined for simulated clusters and Cu modified sol–gel SiO2 thin films