I came across an equation to find band gap from solution state uv-spectra in literature.
Eg= 1242/ lambda onset
where lambda onset is the the onset wavelength identified by drawing tangents to the absorption edges.
However I'm unable to find details or derivations of this equation. Can anyone give me any insights?
Thank you.
Anjana I. The equation you provided is a simple approximation for estimating a material's band gap from the onset wavelength in solution state UV-Visible spectra. It is based on a common empirical relationship between band gap energy and onset wavelength for direct band gap materials. However, this method may not be accurate for all materials, especially those with complex electronic structures. For more accurate determination, more sophisticated methods like Tauc plots or the Kubelka-Munk function can be employed. For more details, consult specific literature or sources. The Tauc plot and Kubelka-Munk function are commonly used for estimating the band gap from solution-state UV-Visible spectra. The Tauc plot plots the absorption coefficient as a function of photon energy or wavelength, while the Kubelka-Munk function estimates the band gap from the intercept of the linear portion with the energy axis. The choice of method depends on the material's nature and UV-Visible spectrum characteristics. The Tauc plot is more commonly used for direct band gap materials:
αhν = A [hν – Eg ]n
while indirect band gap materials may require additional analysis.
It is the Einstein equation
E(J) = hc/lambda
All SI units.
When E use eV as unit, E(eV) = E(J)/e where e is the electron charge,
so E(eV) = (hc/e )/lambda = (6.63E-34*3E8/1.602E-19)/ lambda
where lambda has unit m, if using nm as wavelength unit,
E(eV) = (6.63E-34*3E8/1.602E-19*1E9) /lambda(nm) = 1242/lambda(nm).
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