Optical properties of bismuth trioxide thin films

For Bi2O3 thin films, the influence of preparation conditions on the optical absorption, in the spectral range of 280–1260 nm, was investigated. Bi2O3 films (d = 0.07–1.50 μm) were prepared by thermal oxidation, in air, of vacuum evaporated Bi films. Glass and mica substrates were used. Structural investigations (performed by X-ray diffraction and optical polarizing microscopy) showed that films have a polycrystalline and multiphasic structure. The values of energy gap, Eg (direct transitions), calculated from the absorption spectra, ranged between 2.40 and 3.96 eV. The values of Eg for Bi2O3 films are strongly influenced by the heat treatment characteristics, which determine the phase composition of samples.