Design of a diamond-like infrared nonlinear optical material LiBS2 with ultra-wide band gap

The exploration of new infrared (IR) nonlinear optical (NLO) materials with large second-harmonic generation (SHG) responses and wide band gap (Eg) is an urgent need but challenging. Starting from the superior unit combination strategy and considering the advantages of borates, chalcogenides and Li elements, we have focused our attention on the exploration of IR NLO materials in the Li-based thioborates. Four novel non-centrosymmetric LiBS2 structures, were obtained successfully through crystal structure prediction by analogy and structural optimization based on the thermodynamic and dynamic stability analysis. Among them, LiBS2-I exhibits an ultra-wide band gap Eg = 4.4 eV, moderate SHG response 0.6 × AgGaS2, and suitable birefringence Δn = 0.04 at 1064 nm, which satisfies the good balance between Eg ≥ 3.0 eV and dij ≥ 0.5 × AgGaS2. The role of microscopic units [BS4] in NLO effect was investigated. This work enriches the structural diversity of thioborates and provides a new approach to the exploration of excellent IR NLO materials.