Quaternary Noncentrosymmetric Rare-Earth Sulfides Ba 4 RE 2 Cd 3 S 10 (RE = Sm, Gd, or Tb): A Joint Experimental and Theoretical Investigation.

Multinary rare-earth chalcogenides with d-block transition metals have attracted considerable attention owing to their intriguing structural architectures and promising practical applications. In this work, three quaternary rare-earth sulfides, Ba 4 RE 2 Cd 3 S 10 (RE = Sm, Gd, or Tb), have been obtained by the high-temperature solid-state method. These compounds are isostructural and belong to the noncentrosymmetric orthorhombic space group Cmc 2 1 (No. 36). The basic structural unit contains unique two-dimensional anionic [RE 2 Cd 3 S 10 ] 8- layers, which are separated by Ba 2+ cations. Remarkably, Ba 4 Sm 2 Cd 3 S 10 exhibits a high second-harmonic-generation intensity (1.8 times that of AgGaS 2 ) and a significantly higher laser-induced damage threshold (14.3 times that of AgGaS 2 ), which is the first case possessing an infrared (IR) nonlinear optical (NLO) property in the quaternary AE/RE/TM/Q (AE = alkaline-earth metals; RE = rare-earth metals; TM = d-block transition metals; and Q = chalcogen) systems. Moreover, theoretical investigations of the structure-property relationship indicate that the combined action of various types of NLO-active units makes the main contribution to the SHG activity. This discovery may shed light on broadening the frontiers of IR-NLO materials.