I have just absorption spectra and normally I need thickness to calculate absorption coefficient alpha.
You can not get absorption coefficient from absorption data without knowing the thickness of the film but you can get this from transmission data provided you get interference fringes. You can use Swanapoule method to find out real and imaginary part of refractive index, absorption coefficient, band gap using Tauc plot. You also get the thickness of the film from this analysis. You have to take transmission in large wavelength range 200 nm to 2000 nm to observe interference fringes.
I agree with Dr. A. Kumar. You need the film thickness to calculate absorption coefficient from absorption data. Have you taken care of reflection while calculating absorption? This is important as there is always some reflection from the film.
Dear Adel, in behalf of absorption coefficient I agree with the comments above.
Another question is the band gap energy you asked about. If your material has a band gap, absortion should show a pronounced edge where it falls from some value to near zero. You can take the wavelength of this edge (may be the peak of the first derivative) to calculate the corresponding energy: it should give you an idea about the separation between the valence and the conduction band.
Band gaps of semiconductors fall in the UV-Vis range (1-3 eV).
Good luck
Miguel
I agree with the comments above.
- You can also use the equation; E =1240/lambda if you know the wavelength where the maximum absorption takes place.
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