Absorption edges can often be broad and may not display a sharp cutoff, which makes pinpointing the exact band gap challenging. Therefore, drawing a tangent to the steepest part of the absorption curve could potentially reduce ambiguity, offering a clearer and more precise measurement of the band gap.

Sushil Kumar K C Thank you very much for the answer. I have a follow-up question regarding the attached figure. Is the tangent's position appropriate for determining a band gap of 3.1 eV (as shown in Figure)? As you mentioned, the tangent is typically drawn at the steepest part of the absorption curve. Based on this, it seems the steepest part is closer to 4 eV rather than the 3.5 eV shown in the figure. Could you clarify this?

Best,

Beenish Ajmal.

Hello,

In my opinion you are right, the tangent in the figure should cut the X axis closer to the value of 4 eV. The earlier elevation of the absorption spectrum may be due to scattering of the sample which raises the absorption signal but has nothing to do with the electron transition.

Best Regards,

PW

Beenish Ajmal,

I share the same view with Piotr Wieczorek. The tangent should ideally intersect the x-axis closer to 4 eV to reflect the true optical band gap, as this aligns with the steepest slope of the absorption curve. The earlier rise in the absorption spectrum may indeed be influenced by scattering effects in the sample, which can alter the baseline but do not represent true electronic transitions.