Optically controlled phase variation of TiO₂ nanoparticles

In this paper, we report the anatase-to-amorphous phase conversion of TiO₂ nanoparticles by means of low intensity visible light excitation. A proper choice of power density of the incident radiation and of partial pressure of oxygen in the experimental room allows a local and precise control on the phase of TiO₂ nanoparticles. The 2.54 eV light of an Ar⁺ laser was used to induce structural changes on the samples and to collect photoluminescence spectra, while the 1.96 eV light of a He-Ne laser was utilized for in situ Raman measurements to give immediate proof of the crystallographic structure of the samples. In opposition to other light induced processes, based on the temperature effect, the phase conversion is due to surface modifications by a proper depletion of adsorbed oxygen on the crystal surface.