I have got uv-vis spectroscopic data of tin-oxide in the form of graph of absorbance peak and now i want to find the band gap using Tauc plot.I need alpha(absorbance coefficient )for tauc plot .How can i calculate the value of alpha?
alpha coefficient depend on absorb... energy. Alpha are determinded (normalized) by take the absorbance values (vertical data) divided by the thickness value of measured sample (in cm)
I=I0exp(-alfa/d), d: thickness of film>> calculate alfa >(alfa hv) power of 1/2 or 2 depends on type of band gap direct/indirect (v: frquency) Vs hv > liner fit
"I=I0exp(-alfa/d), d: thickness of film" (Lambert-Beer-Bouguer Law), This equation can be simplified and the absorption coefficient can be obtained from the measured absorption spectra, alpha = ln(I0/I)/d. In this cace, u has a uv-vis spectrum, that mean u receive Absorbance (optical density) = Log I0/I depends on hv. Alpha=Absorbance/d, Alpha (or Absorbtivity) is absorption coefficient (cm-1) , d is a sample thickness and Absorbance values is data from vertical axis of uv-vis spectrum.
Dear friend,
Plz have a look to this paper, It may help
http://www.davidpublisher.com/Public/uploads/Contribute/574697464a3e5.pdf
Dear Tazzy,
In general, The transmittance falls sharply at the band edge, which is an indication of the good films homogeneity. The optical energy band gap (Eg) of the films was obtained by extrapolating the linear part of the spectrum (αhν)2=f(hν) to zero, where α is the absorption coefficient, h the Planck constant and υ is the radiation frequency.
Good luck.
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