Rational Design of a Rare-Earth Oxychalcogenide Nd 3 [Ga 3 O 3 S 3 ][Ge 2 O 7 ] with Superior Infrared Nonlinear Optical Performance.

Inorganic chalcogenides have been studied as the most promising infrared (IR) nonlinear optical (NLO) candidates for the past decades. However, it is proven difficult to discover high-performance materials that combine the often-incompatible properties of large energy gap (E g ) and strong second harmonic generation (SHG) response (d eff ), especially for rare-earth chalcogenides. Herein, centrosymmetric Cs 3 [Sb 3 O 6 ][Ge 2 O 7 ] is selected as a maternal structure and a new noncentrosymmetric rare-earth oxychalcogenide, namely, Nd 3 [Ga 3 O 3 S 3 ][Ge 2 O 7 ], is successfully designed and obtained by the module substitution strategy for the first time. Especially, Nd 3 [Ga 3 O 3 S 3 ][Ge 2 O 7 ] is the first case of breaking the trade-off relationship between wide E g (>3.5 eV) and large d eff (>0.5 × AgGaS 2 ) in rare-earth chalcogenide system, and thus displays an outstanding IR-NLO comprehensive performance. Detailed structure analyses and theoretical studies reveal that the NLO effect originates mainly from the cooperation of heteroanionic [GaO 2 S 2 ] and [NdO 2 S 6 ] asymmetric building blocks. This work not only presents an excellent rare-earth IR-NLO candidate, but also plays a crucial role in the rational structure design of other NLO materials in which both large E g and strong d eff are pursued.