LAUSR

A series of nonlinear optical (NLO) chalcohalides AXHg3P2S8 (A = Rb, Cs; X = Cl, Br), which contain various Hg‐based building units including mixed‐anion trigonal planar [HgS2X]3− and tetrahedral [HgS3X]5−, are successfully synthesized. These compounds display good water resistance, wide infrared transparent region (0.42–17 µm), high laser‐induced damage thresholds (4.5–6 × AgGaS2), and strong phase‐matchable second harmonic generation (SHG) response close to AgGaS2. The mixed‐anion chalcohalide groups serving as functional building units in NLO materials are studied for the first time and proven to be very effective. This work opens a new avenue for new NLO material design to achieve the balance between strong SHG efficiency and large bandgap.