Low-temperature deposition of the high-performance anatase-titania optical films via a modified sol–gel route

Anatase-titania films with high optical performances have been deposited via a modified sol–gel route. This involved several precisely controlled processes including a sufficient hydrolysis of titanium tetraisopropoxide (TTIP) with excessive water, a peptization at pH value of 1–2, a restrained condensation under the hydrothermal conditions at 373 K, and finally a spin-coating process at 293 K. A full characterization of the sols and films indicated that such a well-controlled hydrolysis and condensation of TTIP enabled the formation of high-quality precursor sols consisting of anatase-titania colloidal particles with the mean hydrodynamic diameter of about 17.2 nm, and then endowed the as-deposited films with nanocrystalline structure and the corresponding high refractive index of 1.92 (at 632.8 nm). Moreover, the prepared films exhibited large optical bandgap of 3.38 eV and high laser-induced damage threshold of 16.3 J/cm2 (at 1064 nm, 3 ns pulse duration and R/1 testing mode), which must be closely related to their homogeneous and nearly defect-free network structures derived from the low-temperature sol–gel deposition route.