Zn₂BS₃Br: An Infrared Nonlinear Optical Material with Significant Dual-Property Enhancements Designed through a Template Grafting Strategy

Developing high-performance infrared nonlinear optical (IR-NLO) materials with high second-harmonic generation (SHG) coefficients ( d ij ) and wide band gaps ( E g ) has been a serious challenge owing to the intrinsic negative correlativity between the two key properties. Herein, taking π-delocalized BS 3 as core functional motifs (FMs), a template grafting strategy that facilitates dual-property enhancement is proposed and novel thioborates of Zn 2 BS 3 Br with target IR-NLO performances are predicted by the first-principles evolutionary algorithm. They not only possess wide band gaps of 3.63–4.05 eV, increasing by 1.0 eV over the benchmark AgGaS 2 (AGS, 2.62 eV); moreover, benefiting from the parallel alignments of FMs, five phases exhibit high SHG effects ( d ij > 1.0 × AGS), particularly I (2.0 × AGS & 3.68 eV) and II (2.2 × AGS & 3.77 eV), in which significant enhancements in d ij and E g can be achieved concurrently, surpassing almost all of the accessible IR-NLO materials. Remarkably, the sufficiently wide band gaps and large birefringence of I and II lead to very short phase-matching wavelengths (λ PM = 443.9/370.1 nm), enabling them a dual-waveband application potential, which is rarely found in IR-NLO chalcogenides. In addition, the isomorphic selenides show record high SHG coefficients of 3.8 × AGS in the wide-band-gap range of E g > 3.0 eV. Therefore, the Zn 2 BS 3 Br-family crystals would be promising IR-NLO materials. Profound mechanism explorations conclusively demonstrate the effectiveness of our design strategy.