Optical properties of TiO2 nanoceramic films as a function of N–Al co-doping

The N-doped TiO2, Al-doped TiO2 and N–Al co-doped TiO2 films had the similar structure to that of the TiO2 film and corresponded to nanocrystalline anatase. By N and/or Al doping, the TiO2 film became more stoichiometric and the nanocrystallinity was enhanced, especially N–Al co-doping. The optical transmission of N–Al co-doped TiO2 film was the highest because of the lowest surface roughness and the lowest porosity. The nonlinear refractive index of N–Al co-doped TiO2 film on the glass substrate was measured by Moiré deflectometry, and was of the order of 10−8 cm2 W−1. By N–Al co-doping, the TiO2 nanoceramic film exhibited highest linear refractive index, lowest stress and lowest stress-optical coefficient.