A2SnS5: S tructural I ncommensurate M odulation E xhibiting S trong S econd‐Harmonic G eneration and H igh L aser I nduced D amage Threshold (A = Ba, Sr)

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density wave, however, the thus-induced nonlinear optical property is rare. We report for the first time two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behaviors, A 2 SnS 5 (A = Ba, Sr) with (3+1)D superspace groups P 2 1 2 1 2(00 gamma )00 s or P 2 1 ( alpha 0 gamma )0, featuring different modulations of the [Sn 2 S 7 ] infinity belts. Remarkably, Ba 2 SnS 5 exhibits an excellent second harmonic generation (SHG) of 1.1 x benchmark AgGaS 2 at 1570 nm and a very large laser induced damage threshold (LIDT) of 8 x AgGaS 2 . The theoretical studies uncover the structural modulations increase about 44 or 25% the distortions of the Sn/S building units and enhance significantly the SHG compared with alpha -Ba 2 SnSe 5 without modulation. Besides, despite of having smaller E g , A 2 SnS 5 exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba 2 SnS 5 (1.51) < Sr 2 SnS 5 (2.08) < AgGaS 2 (2.97)).