Single-step synthesis of sub-stoichiometric tungsten oxide particles in mixed acetic and oleic acids: Structural conversion and photoluminescence enhancement

Sub-stoichiometric tungsten oxide (i.e., WO3-x) materials are advanced multipurpose semiconducting materials. However, it is still a challenge to tune their structure and morphology. Here we report the structural and morphological conversion and the photoluminescence (PL) enhancement of the WO3-x materials synthesized in the mixed acetic and oleic acids using tungsten hexachloride precursor. We demonstrate the structural conversion from nanorods to nanodots, accompanied by the morphological change from the mushroom-like particles to the spherical particles. Importantly, the PL emission from the particles aggregated by the WO3-x nanodots is much stronger than the particles aggregated by the WO3-x nanorods. The structural and morphological conversion mechanism is related to the growth rate reduction of WO3-x nuclei and the steric repulsion effect, which are caused by oleic acid. The PL enhancement arises from the reduction of non-radiative recombination caused by the structural conversion and the surface passivation of WO3-x nanodots caused by oleic acid. These results contribute to the commonly needed ability to control the structure of metal oxide nanomaterials and to the development of next-generation functionalities and devices for energy, electronics, optics, and other fields.