Advantageous Units in Antimony Sulfides: Exploration and Design of Infrared Nonlinear Optical Materials.

The exploration of infrared (IR) nonlinear optical (NLO) materials remains attractive because of the urgent requirements in the laser field. Meanwhile, the deepened cognition of structure-property relationships is necessary to help guide the exploration of IR NLO materials. So far, the family of antimony sulfides is an important system with a lot of attention, and a series of antimony sulfides are reported. However, it is urgent to reveal how different Sb-S units, like SbS3, SbS4, and more complex combinations, affect apparent properties. Here, taking ternary metal antimony sulfides as examples, the sources of some essential optical properties, such as second harmonic generation (SHG) and birefringence, are systematically analyzed through first-principles calculations, and the mechanisms of the performances with various magnitudes are also presented to clarify the structure-property relationships. The results indicate that the SbS4 unit among antimony sulfides is an advantageous NLO-active unit, which can balance the contradiction between the band gap and SHG response. Introduction of transition metals in the Sb-S anionic frameworks can tune the magnitude of birefringence. Besides, the substitution of a cation from a transition metal to an alkali metal can notably enlarge the band gap and maintain a large SHG response. These design strategies are beneficial to explore potential IR NLO materials with Sb-S units.