For the metal complexes I have UV-Vis spectra showing various peaks (most cases 2 peaks). Now I want to calculate bandgap using Tauc plot. My question is that using this equation I get two values of band gaps as there are two peaks for my complex. Which should be consider as actual band gap?
The longer wavelength absorption maximum corresponds to the lower energy electronic transition. Whether this is better described as a transition between molecular orbitals (HOMO-LUMO) or semiconductor like bands depends on your material.
Generally, taking the highest wavelength is preferred, since the energy is lower for higher wavelengths. When you're dealing with a crystal structure, the gap will be measured between the top of the valence band and the lowest of the conduction band, so lower gaps translate into new energy levels within the forbidden band when you're comparing two bandgaps.
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