Nanostructure conversion and enhanced photoluminescence of vacancy engineered substoichiometric tungsten oxide nanomaterials

Abstract

Properties of substoichiometric tungsten oxide (WO3-x) semiconducting nanomaterials in diverse applications are morphology-dependent. However, it remains challenging to control morphology and structure of WO3-x nanomaterials. Here, we report the solvothermal synthesis of WO3-x nanostructures with different morphologies in tungsten hexachloride-ethanol solution through adjusting the filling fraction of ethanol in autoclave. The structural and morphological conversion mechanisms are related to the changes in the viscosity and Brownian motion caused by the concentration of tungsten hexachloride in ethanol. The studies on the photoluminescence (PL) properties reveal that the WO3-x nanostructures emit ultraviolet, blue, green and red emissions. The PL emissions are attributed to the recombination between the electron occupying the resonant defect state in the conduction band and the hole in the valence band and the transitions between the conduction and valence bands as well as the transition between the oxygen vacancy states. The enhancement of PL intensity is related to the increase of oxygen vacancies and the phonon suppression during the PL emission as well as the nanocavity structure. Furthermore, the potential applications in the catalysis fields are discussed. These results provide a new technique to control the structure of WO3-x nanomaterials and contribute to the development of next-generation PL emission nanodevices based on vacancy- and structure-engineered WO3 materials and the rational design of catalytic materials.