Preparation and optical characterization of thick-film zirconia and titania ormosils

Crack-free films with thicknesses of up to 30 mu m were prepared by the sol-gel process using the dip-coating technique. Thick films were obtained from various starting solutions based on two, three or four components, with particular emphasis on ternary systems. The ternary systems were composed of two tetraalkoxy precursors (a silicon tetraalkoxide and a zirconium or a titanium tetralkoxide) and a trialkoxysilane with a non-hydrolyzable group. By using these trialkoxysilanes, the tendency of the films to crack during the drying process is reduced because of the stress absorption by the network structure. The use of zirconia or titania allows for control of the refractive index of the films. Optical parameters of the films including refractive index, thickness, surface roughness and UV-Vis and IR transmission spectra were determined for each composition and the structural characteristics of the films were inferred from the IR spectra. UV cut-off and antireflective properties were also studied for some compositions.