Zn₂HgP₂S₈: A Wide Bandgap Hg-Based Infrared Nonlinear Optical Material with Large Second-Harmonic Generation Response

Hg-based chalcogenides, as good candidates for the exploration of high-performance infrared (IR) nonlinear optical (NLO) materials, usually exhibit strong NLO effects, but narrow bandgaps. Herein, an unprecedented wide bandgap Hg-based IR NLO material Zn2HgP2S8 (ZHPS) with diamond-like structure is rationally designed and fabricated by a tetrahedron re-organization strategy with the aid of structure and property predictions. ZHPS exhibits a wide bandgap of 3.37 eV, which is the largest one among the reported Hg-based chalcogenide IR NLO materials and first breaks the 3.0 eV bandgap "wall" in this system, resulting in a high laser-induced damage threshold (LIDT) of similar to 2.2 x AgGaS2 (AGS). Meanwhile, it shows a large NLO response (1.1 x AGS), achieving a good balance between bandgap (>= 3.0 eV) and NLO effect (>= 1 x AGS) for an excellent IR NLO material. DFT calculations uncover that, compared to normal [HgS4]n, highly distorted [HgS4] d tetrahedral units are conducive to generating wide bandgap, and the wide bandgap in ZHPS can be attributed to the strong s-p hybridization between Hg -S bonding in distorted [HgS4]d, which gives some insights into the design of Hg-based chalcogenides with excellent properties based on distorted [HgS4] d tetrahedra.