please find the link
http://www.perkinelmer.com/content/applicationnotes/app_uvvisnirmeasurebandgapenergyvalue.pdf
use tauc plot to find out band gap. i dont know what do u mean by derivative but take the following steps
1)plot absorbance vs wavelength
2) find out portion where obsorbance is coming towards zero i.e sudden drop from highest value to lowest value
3) draw tangent to that portion such that it touches x-axis with some wavelength and obvisoly absorbance=0
4) use these x-axis and y-axis values tauc expression i.e absorbance=0 and wavelenth=...nm. the expression becomes simple E=hc/lambda.
if u want to find out whether ur system is direct or indirect band gap then fit ur curve with tauc expression. find the value of n.
OK Venkat Venki. Find the paper:
file:///C:/Users/nano1/Downloads/09e41507eead49bb27000000.pdf
Dear Sajid, plot a graph between Energy (x-axis) and first derivative of Absorbance with respect to Energy (dA/dE) (y-axis). The value of energy on x-axis corresponds to the maximum of the plot is the Energy Gap.
This link may help sir,
http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/
Which method is accurate one to calculate band gap of Nanomaterials for powder and thin film both ? There were papers i found a decade ago people used to calculate more with derivative method but now a days mostly paper were based on Tauc plot. So it get me confused all time?
Tauc plot is apt to find the bandgap if the transmittance spectrum is almost similar to the ideal transmittance spectrum of a material. In other case one can use derivative method.
see also the references mentioned in https://www.researchgate.net/post/What_is_the_best_experimental_method_for_calculating_of_the_band_gap_of_a_semiconductor_material_what_is_it_based_on
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