Infrared (IR) nonlinear optical (NLO) material is one of the core device of all-solid-state lasers, which show wide applications in long distance laser communication, environmental monitoring and photonic technologies, etc. Currently, the commercially available IR NLO materials are mainly composed of chalcopyrite-like (CL) compounds, like AgGaS₂ (AGS), AgGaSe₂ (AGSe), and ZnGeP₂ (ZGP), which are built by tetrahedral structure units. Nevertheless, the small band gaps (E_g) induced low LIDT and two-photon absorption (TPA) in these materials have limited their further applications in current far-IR laser techniques. Hence, break through the property limitations of CL compounds, developing high performance IR NLO materials based on advantageous structural motifs or new strategies becomes an urgent need.

Recently, a research group led by Prof. Shilie Pan and Prof. Junjie Li at Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Science, designed and fabricated two new IR NLO candidates SrCdSiSe₄ and BaCdSiSe₄ by screening and synergically assembling advantageous structural groups, and fabricated in experiment by simple high-temperature solid-state reaction.The two compounds can be derived from the CSFddd-SrIn₂Se₄withaliovalent tetrahedron substitution, and are constructed by the repeated [B^II₃Si₃Se₁₆] 12-member-ring (MR) consisting of tetrahedral [B^IISe₄] and [SiSe₄] units with A^II atoms. Remarkably,the two compounds possess large SHG responses (2.1-2.7 × AGS), wide band gaps (2.67-2.78 eV) and high LIDTs (4.0 × AGS), achieving a good balancefor an excellent IR NLO candidate. Moreover, DFT calculations reveal that the synergic effect of advantageous [A^IISe₈], NLO-active [CdSe₄] and [SiSe₄] units enhances the shortest board of electronic structure, and keeps the long board of hyperpolarizability, resulting in the wide band gaps and strong NLO responses simultaneously in the title compounds. It confirms the effectiveness of designing high performance IR NLO materials from the known CS compound by the aliovalent group substitution and synergically assembling strategy.

The paper was published in Advanced Functional Materials with the title: SynergicallyAssembling Advantageous GroupsTowardsHigh-Performance Infrared Nonlinear Optical MaterialsA^IICdSiSe₄(A^II= Sr, Ba). This work was financially supported by National Youth Talent Program of China,the Strategic Priority Research Program of the Chinese Academy of sciences, National Natural Science Foundation of China, and Xinjiang Key Research and Development Program.

Figure 1. Synergistic assembly of superior structural motifs achieves balanced key properties in infrared nonlinear optical materials.‌