Figure 4
UV–vis absorbance spectra of the BLT-based powders, (a) BLT, (b) Co-BLT, (c) Fe-BLT. The extrapolation lines (dashed lines) indicates the optical band gap. The Eg value can be obtained by extrapolating the linear segments of the curves towards the x-axis. The optical images of the the doped powers showed clear change of the color with the changes of bandgap energy (inset).