Hello Sir, I am posting some links I hope this articles will help you to realize your problem.. 

http://pubs.acs.org/doi/abs/10.1021/nl034332o

http://aip.scitation.org/doi/abs/10.1063/1.1627962

http://onlinelibrary.wiley.com/doi/10.1002/crat.200710950/full

http://pubs.acs.org/doi/abs/10.1021/j100102a038?journalCode=jpchax

Dear sir..thank you very much for your suggestion and time spent towards the searching of following links to help me out...bless you the god

Dear colleague venkatesha babu kr rathnaiah setty,

Have a nice time and good day,

The increase of dopant concentration of Nano structures may enhance the order of the material, this accompanied by the increasing of optical gap according to the relations through the attached paper there is e inverse proportional between optical gap and refractive index, so the increase of optical gap may accompanied by the increasing of optical gap.

I wish this is useful and help you.

Yours

A. EL-Denglawey