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How can we construct a tauc plot using data from the transmission spectra? How does one calculate the absorption coefficient for plotting tauc plots?

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The absorption coefficient, $\alpha$, is defined by:

$$ \frac{I}{I_0} = e^{-\alpha z} $$

where $I$ is the intensity of the transmitted light and $I_0$ is the intensity of the incident light and $z$ is the optical path length (typically the film thickness). In a transmission spectrum you measure $T$ where $T = I/I_0$, so:

$$ \alpha = - \frac{\ln T}{z} $$

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