Sir, I meant to ask how refractive index depends on optical band gap. In some papers i read optical gap increases/decreases with R.I of the glass and in some other papers i read their inverse dependence.
Ideally,the two should be related by L-L equation but up to certain mol% of the modifier.
It is well known that the modifier metal ion enters the pores of the glass; breaks the tetrahedral O-M-O bonds and finally change BO to NBO.This changes the polarizability which, in turn, changes the band gap.
But this happens up to a limit.For example, up to 0.4 mol%, of Sm2O3 in ZnO-V2O5 glass, the refractive index increases but the value decreases at 0.5mol% .The reverse is the trend in band gap.
“This is due to the change in density and the molar volume which alters the number of pores and there by the NBO vs BO ratio changes irregularly and thus shows an irregular change in band gap versus the refractive index values.”
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