“Three‐in‐One”: A New Hg‐Based Selenide Hg7P2Se12 Exhibiting Wide Infrared Transparency Range and Strong Nonlinear Optical Effect

Abstract The exploration of high‐performance mid‐ and far‐infrared (IR) nonlinear optical (NLO) crystals is an urgent need. Herein, a new Hg‐based selenide Hg 7 P 2 Se 12 (HPSe) is designed and synthesized by a rigid and flexible units coupled strategy. It is interesting that in the compound, three types of NLO‐active units, including linear [HgSe 2 ], triangular [HgSe 3 ], and tetrahedral (MSe 4 ) (M = Hg/P) groups, simultaneously exist. It shows a wide transparency range (0.84–22.8 µm), large SHG response (1 × AGS), high laser‐induced damage threshold (≈2 × AGS), and a large birefringence (0.102 @ 2090 nm). Moreover, the compound melts congruently along with good crystal growth habits, and single crystals with a maximum size of ≈7 × 5 × 2 mm 3 are obtained. Theoretical analyses confirm that the large NLO response originates from the synergistic effects of Hg–Se units, (PSe 4 ) and nonbonding electrons. The results indicate that HPSe is a promising mid‐ and far‐IR NLO material, and inspire a path to finding new classes of IR NLO materials that are different from traditional chalcopyrite materials by grouping the linear, planar, and tetrahedral units.