Please mention the way of calculation also, or provide the link of related article.
Thank You.
Hi. I measured diffuse reflectivity in %R plotting %R against wavelength using UV-Vis.
After that,
use kebulka-munk function to convert %R to absorbance or F(R) against eV graph.
then plot (ahv)^0.5 against eV for direct band gap. (tauc plot)
Extrapolate the slope of the horizontal s-curve to x-axis. the line passed through the x-coordinate is the band gap.
But you can guess the type of transition by looking how steep is the slope in the absorption coefficient against eV graph. Sharp slope (absorption over a short range of energy) show direct transition so a tauc plot of ahv)^0.5 against eV is plotted to determine an accurate band gap.
If the slope has absorption over a wide range of energy , it shows indirect band gap. thus tauc plot (ahv)^2 against eV can be plotted.
one of the simplest method is absorption edge. it is 1240/onset absorption. It directly gives you band gap. here is the reference.
After you measured the UV-vis-NIR absorption spectrum, take the wavelength as the the absorption intensity start to take off .Then you can calculate the band gap energy by using equation: Eg (eV) = 1240/(wavelength in nm). For example, if the intensity arises from the baseline at 340 nm, then you have a material with band gap of 3.65 eV.
Here you can find good explanation and band gap calculator,
http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/
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