Theoretical Design of Layered AlGaS3 as a New Nonlinear Optical Material with a Strong Second Harmonic Generation Response

Using an evolutionary algorithm combined with first-principles calculations, the stoichiometry and the structure of a new family of Al–Ga–S ternary sulfides are explored, and a layered configuration with the R3m space group is predicted as the most stable structure of AlGaS3. The second order nonlinear optical (NLO) properties of the AlGaS3-R3m phase are further calculated, and our results reveal that it is a promising candidate for mid-infrared NLO material. Besides the high laser damage threshold and the good phase match ability in the transmission range 0.4–24 μm that covers most of the mid-IR windows, the second harmonic generation (SHG) of AlGaS3-R3m is about four times stronger than that of the commercial AgGaS2 crystal. The strong SHG activity of the AlGaS3-R3m phase can be attributed to a special layered arrangement of the structure, namely, two kinds of coordination polyhedra (i.e., [AlS6]9– octahedra and [GaS4]5– tetrahedra) are distributed in the opposite sides of the single AlGaS3 layer, which...