LiBaGaQ (Q = S, Se): Noncentrosymmetric Metal Chalcogenides with a Cesium Chloride Topological Structure Displaying a Remarkable Laser Damage Threshold.

The exploration of novel infrared nonlinear optical (IR NLO) materials with large second-harmonic generation (SHG) responses and wide band gaps has become very imperative recently. Herein we reported two noncentrosymmetric compounds, LiBaGaQ (Q = S, Se), crystallizing in space group 42 (No. 114), which feature 3D frameworks built by a basic [GaQ] windmill cluster and LiQ tetrahedra in a cesium chloride topological structure. Both compounds satisfy the desired balance between good SHG responses (∼1.5× that of AgGaS) and wide band gaps (3.43 and 2.44 eV) with remarkable laser damage thresholds (21× and 6× that of AgGaS). The theoretical calculations uncover that the [GaQ] cluster makes major contributions to the SHG effect in LiBaGaQ. In addition, the structure-performance relationship among all compounds in the I-II-III-VI system has been discussed systematically, which indicates that the introduction of the alkali metal lithium in the I site is beneficial for the production of large band gaps. This work will be helpful in exploring novel IR NLO materials with special structures and comprehensive properties in the chalcogenide system.