Na6Sn3P4S16: Sn(ii)-chelated PS4 groups inspired an ultra-strong SHG response

Abstract

The discovery of new infrared nonlinear optical (IR NLO) materials with a large second harmonic generation (SHG) effect and broad optical bandgap is still a challenging task. Based on this, we propose a rational strategy for the design of new NLO materials: (i) the coupling of stereochemically active lone-pair (SCALP) Sn(II) cations and typical PS₄ units into a structure enhances the SHG response; (ii) the incorporation of an alkali metal (Na⁺) cation benefits the preservation of a relatively wide bandgap, which affords the discovery of a new promising IR NLO thiophosphate, Na₆Sn₃P₄S₁₆. It exhibits an ultra-strong SHG response (6.6 × AgGaS₂) and relatively wide bandgap (2.52 eV) that is better than those of known NLO SnPS₃ (1.1 × AgGaS₂ and 2.35 eV). Remarkably, Na₆Sn₃P₄S₁₆ exhibits the largest SHG response among all known IR NLO thiophosphates with bandgaps greater than 2.50 eV. Such an ultra-strong SHG response in Na₆Sn₃P₄S₁₆ originates from the collaborative polarization of edge-sharing SnS₄ and PS₄ units. This work inspires a new way to design new IR NLO thiophosphates with enhanced SHG responses by introducing Sn(II)-chelated PS₄ groups into structures.