The emission properties of carbon dots (CDs) have already found many potential applications, from bio-imaging and cell labelling, to optical imaging and drug delivery, and are largely investigated in technological fields, such as lighting and photonics. Besides their high efficiency emission, CDs are also virtually nontoxic and can be prepared through many green chemistry routes. Despite these important features, the very origin of their luminescence is still debated. In this paper, we present an overview of sounding data and the main models proposed to explain the emission properties of CDs and their tunability.

The light-induced phase transition of TiO2\ud nanoparticles from anatase to rutile structure is reported\ud depending on the surrounding environment, the transition\ud being accomplished under oxygen-poor conditions. The\ud transition mechanism is interpreted in the framework of oxygen\ud adsorption and desorption phenomena with the involvement of\ud surface oxygen vacancies and F centers. It is shown that the\ud observed phase transition is not thermally driven because the\ud local temperature of the nanoparticles during irradiation is\ud about 370 K (estimated through the Stokes to anti-Stokes\ud Raman peaks ratio). On the contrary, the phase transition is\ud initiated by intragap irradiation (with the exception of the red\ud light one) that acts as TiO2 surface sensitizer, promoting the\ud activation of the surface and the nucleation of rutile crystallites starting from two activated anatase neighboring nanoparticles

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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.