HgCuPS4: An Exceptional Infrared Nonlinear Optical Material with Defect Diamond-like Structure

Infrared nonlinear optical (IR-NLO) crystals possessing excellent comprehensive performance are highly desirable, yet their preparation remains extremely challenging. Particularly, inorganic chalcogenides with diamond-like (DL) structures provide a tunable material platform for their structural design and functional control. In this work, a strategy involving the construction of chalcogenides with DL structures using the strong polarizability of metal cations has been put forward; thus, a quaternary Hg-containing metal sulfide HgCuPS4 has been successfully discovered by the high-temperature solid-state technology. A remarkable structural characteristic of HgCuPS4 is the three-dimensional (3D) defect DL framework constructed by vertex-sharing alignments of asymmetric building motifs (ABMs). The combination of the unique defect DL structure and the strong polarizability of the Hg2+ cations enables such compound to achieve phase matchability in the IR range with a high laser-induced damage threshold (4.2 x AgGaS2) and a strong second harmonic generation response (d(ij) = 6.5 x AgGaS2), the best among the quaternary DL chalcogenides reported so far. Moreover, the detailed local dipole moment calculations and the theoretical results based on the length-gauge formalism elucidate that the very high d(ij) value of HgCuPS4 originates from the combined effects of distorted [HgS4], [CuS4], and [PS4] ABMs, that is, the 3D defect DL structure. This discovery can effectively help understand and design other promising defect DL metal chalcogenides toward future high-performing IR-NLO applications.