Colloidal fluorine-doped ZnO quantum dots: the synergistic action of atomic doping and growth conditions directs fluorescence and photoactivity

Quantum dots are nano-sized semiconductor particles showing peculiar optical properties due to the quantum confinement effect. They can efficiently absorb photons and generate excitons, leading to a stable fluorescence emission decisive to designing light-sensitive devices, or they can exert a pronounced photoactivity that favors their use in photocatalysis and photodynamic fields. Among the inorganic quantum dots, ZnO ones show unique optical and electronic properties together with low toxicity, good biocompatibility, and excellent photochemical stability. These features can be deeply influenced by tuning their size, surface, and/or bulk defects as well as by doping. Doping with anionic atoms represents an intriguing alternative to cationic metals to improve ZnO activity. Here, the emission behaviour and photoactivity of fluorine-doped ZnO quantum dots were simultaneously studied as a function of fluorine content and synthesis conditions (e.g., wet-precipitation or solvothermal) adopted for the fabrication. The obtained results demonstrated that a low fluorine content (<5 nominal at%) was pivotal to induce a significant enhancement of the relative emission quantum yield of quantum dots from the wet-precipitation route, while a high photocatalytic activity was guaranteed for those obtained by a solvothermal strategy due to the bulk distribution of atomic defects.