Best way to calculate UV-Vis absorption onset?

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To determine the absorption onset in UV-Vis spectra for calculating optical band gaps, one effective method involves plotting wavelength against (wavelength*Absorbance)^2 and fitting the linear portion to find the intercept. Additionally, calculating the first derivative of the absorbance spectrum and identifying the zero point after the last saddle point can also indicate the onset. Tauc plots are commonly recommended for this analysis. These methods provide a systematic approach to accurately identify the optical band gap. Proper application of these techniques can enhance the reliability of the results.
Dan Zar
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Homework Statement


Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

Homework Equations

The Attempt at a Solution


I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
 
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Dan Zar said:

Homework Statement


Hello,
I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

Homework Equations

The Attempt at a Solution


I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
Tauc plots are typically used.
 

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