thin films of binary bi 0 -teo and bi 0 -v 0 systems were prepared by the thermal co-evaporation technique in a vacuum at room temperature. the optical absorption edge of these systems are studied in the wavelength of 200-800 nm using a perkin-elmer uv/vis spectrophotometer. it is found that the value of n=3/2 in the davis-mott equation is best fitted for the fundamental absorption edge for the...