Emissive titanium dioxide nanoparticles synthesizedpy pulsed laser ablation in liquid phase

The remarkable applications of TiO2 nanomaterials, including, e.g. photocatalysis and dye-sensitized solar cells, have inspired in the last two decades an extensive amount of research aimed at understanding the properties of these materials. Photoluminescence is scarcely used to probe the electronic properties of TiO2, because neither bulk or nanosized TiO2 commonly display room-temperature emission. In particular, the fundamental luminescence due to the recombination of the self-trapped exciton in anatase TiO2 is typically observed only at low temperatures. We report the synthesis of luminescent titanium dioxide nanoparticles (NPs) by pulsed laser ablation of titanium in aqueous solution. The ablation procedure yields a colloidal solution of nano-sized TiO2 in a mixture of the anatase and rutile forms, as verified by Raman measurements. Atomic force microscopy shows that the average size of the primary NPs is about 4 nm. Their absorption spectrum in water features a fundamental threshold at about 3.5 eV, slightly blue-shifted with respect to the characteristic value of bulk TiO2. Interestingly, photo-excitation in the UV gives rise to an emission band centered at 420 nm with a lifetime of about 6 ns. More experiments are being carried out to identify the nature of the emitting electronic transition.