Metal lone pairs play an important role in determining the SHG enhancement and bandgap red shift. In this work, the electronic structures and optical properties of a class of lead borates Pb2B5O9Cl, BaPb[B5O9(OH)]·H2O, and Ba2Pb(B3O6)2 have been investigated to uncover the influence of the lead atom on the band gap and SHG response. It is found that BaPb[B5O9(OH)]·H2O and Ba2Pb(B3O6)2 have little bandgap redshift due to their weak distortion and stereochemical activity. The intensity of the lead lone pair stereochemical activity plays an important role in determining the reduction of the band-gap.
