S. A. Babanejad, F. Ashrafi and N. Salarzadeh, E. Ashrafi
Using optical absorption and studying the edge – absorption of either crystalline or amorphous structures, is an efficacious and useful method for better realizing the electronic structure of these materials. In this paper, firstly, we prepared the bulk specimens of different percentages of B2O3 and CdO in form of binary systems, and then we studied UV- Visible spectrums of specimens in the range of 200–800 nm. After determination of absorption coefficient α (ω,) then we traced out (αћω) 1/n against (ћω) diagrams for obtaining the value of n. In this research, by considering n=2, we have obtained a linear diagram with exponential tail. Therefore, according to Mott and Davis’s statement, it was established that, the type of transition is indirect allowed. By extrapolating the linear part of (αћω) 1/2 against (ћω) diagram, we determined the optical gap energy (Eopt) at (αћω) 1/2 = 0. The obtained amounts of Eopt (2.505 to 2.965 eV) show that, Eopt decreases with increasing in CdO percentage. By tracing the plot of variation of ln α (ω) against (ћω), we have determined the slope of the linear part of diagram, which is equal to width of localized states ΔE (about 0.469 to 0.811 eV).
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