A reviewer asked me to change my UV/vis diffuse reflectance spectrum (Tauc plot) to Kubelka-Munk plot. My Figure looks as in attachment. I dont know what does he/she want? Should the bandgap change when we change from Tauc plot to Kubelka-Munk plot?
Thanks for any idea.
Dear Sovan,
I think for the first it is necessary to clarify that UV/vis diffuse reflectance spectrum and "Tauc plot" are not the same thing.
When you perform a diffuse reflectance analysis you have as answer the reflectance curve as function of the wavelength. This curve can be converted in a equivalent absorption curve according to the Kubelka-Munk theory:
F(R)=(1-R)^2/2R=alpha(lambda)/S(lambda)
where F(R) is the Kubelka-Munk; R=Rsample/Rstandard; alpha(lambda) is the absorption coefficient and S(lambda) the scattering coefficient for the measured sample.
Considering the scattering coefficient S wavelength independent, it can be assumed that F(R) is aprroximately proportional to the absorption coefficient alpha.
The Tauc plot method assumes that the absorption coefficient alpha is related to the energy band gap (Eg) by the following equation:
alpha*hv = A(hv-Eg)^n
where A is a proportionality constant and n an index related to the specifical electronical transition (1/2 direct allowed; 3/2 direct forbidden; 2 indirect allowed; 3 indirect forbidden).
For diffuse reflectance measurements, thanks to the Kubelka -Munk theory, the same equation can be written as:
F(R)*hv = A(hv-Eg)^n
So the plot you attached above it is not a reflectance spectrum (or an equivalent absorption spectrum too), but is the so called "tauc plot" obtained for n=1/2.
Dear Sovan,
I think for the first it is necessary to clarify that UV/vis diffuse reflectance spectrum and "Tauc plot" are not the same thing.
When you perform a diffuse reflectance analysis you have as answer the reflectance curve as function of the wavelength. This curve can be converted in a equivalent absorption curve according to the Kubelka-Munk theory:
F(R)=(1-R)^2/2R=alpha(lambda)/S(lambda)
where F(R) is the Kubelka-Munk; R=Rsample/Rstandard; alpha(lambda) is the absorption coefficient and S(lambda) the scattering coefficient for the measured sample.
Considering the scattering coefficient S wavelength independent, it can be assumed that F(R) is aprroximately proportional to the absorption coefficient alpha.
The Tauc plot method assumes that the absorption coefficient alpha is related to the energy band gap (Eg) by the following equation:
alpha*hv = A(hv-Eg)^n
where A is a proportionality constant and n an index related to the specifical electronical transition (1/2 direct allowed; 3/2 direct forbidden; 2 indirect allowed; 3 indirect forbidden).
For diffuse reflectance measurements, thanks to the Kubelka -Munk theory, the same equation can be written as:
F(R)*hv = A(hv-Eg)^n
So the plot you attached above it is not a reflectance spectrum (or an equivalent absorption spectrum too), but is the so called "tauc plot" obtained for n=1/2.
Dear Antonio,
It is really helpful explanation to clarify my problem.
Thanks you so much.
Best Regards
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