Thermal growth, structural and optical characterization of hierarchical Bi₂O₃ - MoO₃ nanostructures

Branched α-Bi₂O₃ nanowires decorated with MoO₃ nanoplates have been grown by a two–step sequential evaporation–deposition method. Their morphology, structural, compositional and luminescence properties were investigated by a set of spatially-resolved characterization techniques including scanning and high-resolution transmission electron microscopy (SEM, HRTEM), energy dispersive X-ray microanalysis (EDX), micro-Raman spectroscopy and cathodoluminescence (CL) in a SEM. Different zones can be distinguished in these complex structures. Close to the tips, the α-Bi₂O₃ nanowires appear covered by a high density of α–MoO₃ nanoplates, as revealed by the SEM, HRTEM and micro-Raman observations. The Bi₂O₃ trunks of these hierarchical arrangements appear covered by a lower density of nanoplates, which decreases towards the base of the structures. Besides α–MoO₃, Raman measurements reveal the existence of crystals of other MoO₃ phases, as well as different Mo oxides, in these zones. CL spectra from the different regions show emission bands related to oxygen vacancies and Bi³⁺ intraionic transitions in α-Bi₂O₃, while luminescence emission of the MoO₃ nanoplates is mainly related to complex defects involving Mo⁵⁺ ions and oxygen vacancies. - Highlights: • Hierarchical Bi₂O₃ - MoO₃ nanostructures were grown by a thermal deposition method. • Structural and compositional properties were studied by spatially-resolved techniques. • Phase assessment of the Mo oxides nanoplates by confocal micro-Raman spectroscopy. • Luminescence properties of the nanostructures were investigated by SEM cathodoluminescence.