I have recorded the UV-absorption spectrum of my sample (bismuth titanate). I wish to know how we can determine the exact bandgap based on the tauc plot, if the absorption coefficient is unknown?
Absorption coefficient you can find out from Beer Lambert's law, i.e if you know the concentration of your sample and have absorbance value, you can calculate coefficient. Otherwise also if you have calibration graph of your sample absorbance, from slope you can calculate coefficient