Correlation of large SHG responses with structural characterization in borophosphate niobium glasses

Transparent and homogeneous sodium borophosphate niobium glasses with good optical quality were obtained for Nb₂O₅ proportion up to 50 mol%. Large NLO second-order susceptibilities, up to 5 pm/V for the highest niobium loading, are generated through an efficient thermal poling process which induces a strong space-charge migration of Na⁺ cations. From combined IR, Raman and thermal analyses, we establish that the observed strong increase of χ⁽²⁾ responses with niobium concentration is linked to the extent of the niobium–oxygen 3D structure which enhances the third-order susceptibility.