Understanding the effect of bound excitons on two photon absorption process in anatase TiO2 nanospheres using ultrafast pulses

Nanoparticles of Titanium dioxide (TiO2) with its unique optical and electronic characteristics is an important material for photochemical catalysis. The efficiency of catalytic activity of TiO2 anatase nanostructures is greatly influenced by the photo-generated bound excitons. It is found that the interaction of bound excitons generated in TiO2 enhances the cubic nonlinearity of the system due to strong oscillation of photo-generated bound excitons. The trapped electron hole pair concentration is directly proportional to the photocatalytic efficiency of the TiO2 anatase nanostructures. In our report, we show how these photo-generated bound excitons play a significant role in origin of third-order optical nonlinearities. In particular, we have measured large phase shift and seen two photon absorption process through closed and open aperture Z-scan, respectively, using femtosecond pulses at 532 nm.