Strong Second Harmonic Generation in a Tungsten Bronze Oxide by Enhancing Local Structural Distortion

To discover the nonlinear optical (NLO) materials with strong second harmonic generation (SHG), the design of NLO-active molecular units with large polarization is considered as a common strategy. Herein, we propose that the local structural distortion induced with vacancies, apart from the NLO-active units, can be employed to improve the NLO effect in solids as well. Accordingly, a new tungsten bronze (TB) oxide, Pb 2 (Pb 0.15 Li 0.7 □ 0.15 )Nb 5 O 15 (□ representing vacancies), is successfully designed and prepared, which exhibits a strong SHG response of 39 times that of KH 2 PO 4 . The detailed analysis reveals that the local structural distortions enhanced by the vacancies in PLN strengthen the local dipole moments of neighboring NbO 6 octahedra, and thus significantly prompt the SHG effect. Moreover, a series of new TB compounds with large NLO effects are discovered by this molecular design strategy, which are perspectives for new NLO materials synthesis.