ABSTRACT
The strong mutual coupling of and even the opposite change in the key parameters, such as the band gap (Eg ) and second-order harmonic generation (SHG), leads to the extreme scarcity in high-performance IR nonlinear optical (NLO) chalcogenides. Herein, we report 8 new sulfides, Na2 Ba[(Agx Na1-x )2 Sn2 S7 ] (1, x=0; 1â series, x=0.1-0.6; Na2 Ba[(Li0.58 Na0.42 )2 Sn2 S7 ], 1-0.6Li); Na2 Sr[Cu2 Sn2 S7 ] (2); and Na2 Ba[Cu2 Sn2 S7 ] (3). We use the structural tolerance factor ( t I e x p ${{t}_{I}^{exp}}$ ) to connect the chemical composition, crystal structure, and NLO properties. Guided by these correlations, a better balance between Eg and SHG is realized in 1, which exhibits a large Eg of 3.42â eV and excellent NLO properties (SHG: 1.5×AGS; laser-induced damage threshold: 12×AGS), representing the best performance among the known Hg- or As-free sulfides to date.
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, A2 SnS5 (A=Ba, Sr), with the (3+1)D superspace groups P21 21 2(00γ)00s or P21 (α0γ)0, featuring different modulations of the [Sn2 S7 ]∞ belts. Remarkably, Ba2 SnS5 exhibits an excellent second harmonic generation (SHG) of 1.1â
times that of the benchmark compound AgGaS2 at 1570â
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 A2 SnS5 (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α-Ba2 SnSe5 without modulation. Besides, despite the smaller Eg , the A2 SnS5 samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba2 SnS5 â
(1.51)
