No abstract

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density waves; however, thus‐induced nonlinear optical properties are rare. We report herein two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behavior, A2SnS5 (A=Ba, Sr), with the (3+1)D superspace groups P21212(00γ)00s or P21(α0γ)0, featuring different modulations of the [Sn2S7]∞ belts. Remarkably, Ba2SnS5 exhibits an excellent second harmonic generation (SHG) of 1.1 times that of the benchmark compound AgGaS2 at 1570 nm and a very large laser‐induced damage threshold (LIDT) of 8×AgGaS2. Theoretical studies revealed that the structural modulations increase the distortions of the Sn/S building units by about 44 or 25 % in A2SnS5 (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α‐Ba2SnSe5 without modulation. Besides, despite the smaller Eg, the A2SnS5 samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba2SnS5 (1.51)

Band gap tuning is at the core of current optical and electronic device applications, the wide-band-gap chalcogenides are especially challenging and highly desired in many fields, such as nonlinear optical materials. On the basis of our in-depth investigation on the complicated cubic AII 6(BI 2CII)­DIV 4S16 family, we reveal that the structural complexity causes the band gap tuning to be determined by multiple factors, in which a “bucket effect” is uncovered. Guided by such a bucket effect strategy, we rationally synthesized two new members, Sr6(Li2Cd)­A4S16 (A = Ge (1; a = 13.916 Å), Sn (2; a = 14.237 Å), via a site-specific substitution. 1 exhibits the widest band gap (3.8 eV) in this family known to date. Benefiting from their wide band gaps, 1 and 2 exhibit excellent laser irradiation duration capability, with laser-induced damage thresholds (LIDTs) of 55.5 and 44.4 MW/cm2 at a 1.064 μm incident laser, which are 21 and 17 times higher than that of the benchmark AgGaS2 (2.69 MW/cm2). Especially, the LIDT of 1 is the highest known to date among the cubic AII 6BI 2CIIDIV 4S16 family. Our insight into the band gap tuning in a complex system should shed useful light on the future design of functional materials and band gap engineering.