Dear Gawai

Stacking faults change atoms order in the nanocrystal as a result it introduces new energy line levels. If these levels happened to be inside the energy gap the energy gap is reduced in value. If these levels are not inside the gap the gap remains at its value. In either of the cases UV-Vis is changed due to transitions to and from the new energy levels.

Respected Mudar A. Abdulsattar sir

   Thank you very much for answer of my question, it is helpful to referee response of RSC Adv. 

As a first estimate, you can compare the bandgaps of cubic (sphalerite) and hexagonal (wurtzite) modifications of the same semiconductor, because a stacking fault or twin basically changes only the atomic stacking order of planes. You will find that for most semiconductors, the differences are minute and subject to some debate.  For GaAs twins, we e.g. did not find any changes in EELS within ~0.1eV energy sensitivity (published in Cryst. Res. Technol. 50, No. 1, 62–68 (2015) / DOI 10.1002/crat.201400166). Yours, Thomas

Respected sir,

Thanks for the same