Dear Smruti,

Welcome,

Hope you are well!

Thank you for inviting me to reply this question.

You have to repeat this experiment to be sure that your results are reliable.

I think the difference in the three cases may be due to the size of the nanowires.

As the size increases the Bandgap decreases.

But one has to verify this hypnosis by measuring the thickness of the wires.

Other effect may be due to the passivation of the surface states.

This leads to the reduction of the electronic states in the bandgap which leads to reducing the bandgap.

Please advice you to read in the energy band structure of fine grained and amorphous silicon.

Best wishes

Thank you @Abdelhalim Zekry . I have repeated the experiment twice and got the same kind of changes in the peak values. Size remains same for all the samples.

I agree with Abdelhalim abdelnaby Zekry , the redshift in the band gaps of H-passivated and OH passivated Si nanowires can arise due to the surface passivation (termination of dangling bonds at the surface). As a result of the passivation sub-energy levels can be formed within the band structure of host material and contribute to the radiative recombination. In this case the PL intensities for H-passivated and OH-passivated samples should be relatively higher than pristine sample (untreated sample) which actually indicate the relatively lower defects concentration in the passivated samples.

The observed redshift for your PL may be caused by the evolution of surface defects related to your post-processing of Si nanowires that accompanied by the creation of radiative centre below the conduction band.

Thank you @ Ali Imran channa @ Ahmed Galal Abdelrehim

I think that the main reasons for these different treatment came from firstly the size of nanowire which inversely proportional with the energy gap . Secondly the variation in surface state , which may be reduced the energy gap