I have synthesized cobalt oxide and I got two bandgap from the UV_Visisble absorption spectra.
Semiconductor materials have both, direct and indirect gaps. Generally, direct gap is observed in thin samples whereas indirect gap requires thick samples. However, in disordered or heavily doped samples a shoulder can be observed at energies lower than Eg.
Best regards
Pedro
Do you checking structure of obtained material? What material you are synthesized? CoO or Co3O4??? May be you have the mix of these materials??? In this case you will get 2 band gap.
Qiao, L., Xiao, H. Y., Meyer, H. M., Sun, J. N., Rouleau, C. M., Puretzky, A. A., … Biegalski, M. D. (2013). Nature of the band gap and origin of the electro-/photo-activity of Co3O4. Journal of Materials Chemistry C, 1(31), 4628. doi:10.1039/c3tc30861h
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