Non resonant excitonic effects on the third order nonlinear properties of TiO2: From amorphous to rutile phase

• Spectral and nonlinear optical investigation has been performed on TiO2 and its widely used two polymorphs, anatase and rutile.
• Anatase is found to possess the highest nonlinearity owing to the presence of bound excitons.
• Optical limiting performance was evaluated for all the three polymorphs of TiO2.

We present the linear and nonlinear optical studies on amorphous TiO2 and its major polymorphs, anatase and rutile. Optical band gap is found to vary with annealing temperature. The fluorescence emission spectra confirmed the presence of more imperfections and disorders in anatase than in rutile phase. Nonlinear optical properties are studied using both open and closed aperture Z-scan technique. Anatase phase is found to show better nonlinear properties and this has been attributed to the dominant role played by the excitons.