Zwitterionic Glycine-Based Antimony Fluorides with Exceptional Ultraviolet Nonlinear Optical Properties

초록

Despite significant advancements in ultraviolet nonlinear optical (UV NLO) materials, a systematic design strategy remains elusive. This study introduces an approach to enhance NLO performance by utilizing zwitterionic units. Two antimony fluoride compounds, alpha -2SbF 3 <middle dot>Gly and beta -2SbF 3 <middle dot>Gly, were synthesized by combining glycine zwitterions with Sb3+ cations and highly electronegative F- anions. The structure of alpha -2SbF 3 <middle dot>Gly belongs to the polar noncentrosymmetric space group, Ia (No. 9), while beta -2SbF 3 <middle dot>Gly adopts the centrosymmetric space group, P21/c (No. 14). The metastable alpha -2SbF 3 <middle dot>Gly undergoes an irreversible phase transition to the thermodynamically stable polymorph, beta -2SbF 3 <middle dot>Gly, at 160 degrees C. Notably, alpha -2SbF 3 <middle dot>Gly exhibits an optimized arrangement of glycine zwitterions and SbF3 polyhedra, interconnected through hydrogen bonding. This structural configuration imparts exceptional optical properties, including a strong second-harmonic generation intensity 3.3 times that of KH2PO4, a wide band gap of 4.78 eV, and a suitable birefringence of 0.146 at 546 nm, highlighting its potential as an advanced UV NLO material. This work underscores the promise of zwitterionic units as a powerful design tool for UV NLO materials, providing a foundation for the development of next-generation NLO technologies.

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