Multiphase tungsten trioxide powders: Structure, morphology, band gap and cathodoluminescence

Tungsten trioxide (WO3)-powders were obtained by thermal evaporation in a hot-filament chemical vapor deposition system, and were characterized by X-ray diffraction, UV-Vis, field-emission scanning electron microscopy, and cathodoluminescence measurements. The powders were obtained under different ambient gas (argon, argon plus water vapor, or air), which determined the oxygen partial pressure (OPP) into the reactor. The (WO3)-powders exhibited multiphase characteristics, although the band gap of all samples matched well with that of the WO3 structure. Morphology of the (WO3)-powders changed from nanowires, then to nanowires-rhombohedrons-spheres, and finally to rhombohedrons-spheres with the increase of the OPP. Similarly, intensity of the intrinsic versus defect-state cathodoluminescence emissions were also depended on the OPP.