Effect of Additives on Synthesis and Optical Property of Metastable γ-Bi₂O₃

Metastable γ-Bi₂O₃ was prepared via a solution precipitation method in ethylene glycol-water solvent system at 80℃ for 40 min by ambient atmospheric pressure with Bi(NO₃)₃·5H₂O as bismuth source and NaOH as precipitant. The effect of additives (glycerol, TrionX-100, CTAB, SDBS, ethanol, and oleic acid) on the microstructure and optical properties of metastable γ-Bi₂O₃ were investigated by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), ultraviolet-visible spectrum (UV-VIS) and Fluorescence spectrum (PL). The as-prepared product composed mainly of γ-Bi₂O₃ and little α-Bi₂O₃ with dimensions of submicron to micron. Products with diversified morphologies such as cube, tetrahedron, and three-dimensional self-assembled hierarchical flower-like respectively were obtained by adding different additives. UV-visible diffuse reflectance spectrum shows that the product presents photo-absorption property from UV light-to visible light-range, which belongs to the absorption caused by electron transition from valence band to conduction band, that is Bi₂O₃ direct band gap absorption. The band gaps of Bi₂O₃ are estimated to be 2.30~2.81 eV for different additives. The fluorescence spectrum of the product shows broad emission (400~600 nm) with 5 emission bands (their center located at 449 nm, 466 nm, 480 nm, 491 nm, and 561 nm). The results also show that the additive not only has an important effect on the purity and microstructure of the product, but also has a significant effect on the crystal structure, which will change the physical and chemical properties (such as light properties) of the materials. By adding additives, the final bandgap width of the products can be adjusted.