An investigation of new infrared nonlinear optical material: BaCdSnSe4, and three new related centrosymmetric compounds: Ba2SnSe4, Mg2GeSe4, and Ba2Ge2S6

Abstract

A series of new metal chalcongenides, BaCdSnSe₄ (1), Ba₂SnSe₄ (2), Mg₂GeSe₄ (3), and Ba₂Ge₂S₆ (4), were successfully synthesized for the first time. Among them, compounds 2 and 4 were prepared by a molten flux method with Zn as the flux. In their structures, all of them have MQ₄ (M = Sn, Ge; Q = S, Se) units. For compound 1, the CdSe₄ and SnSe₄ groups are connected to form CdSnSe₆ layers and these layers are linked together by the Ba atoms. Compounds 2 and 3 are composed of isolated MSe₄ (M = Sn, Ge) units and charge-balanced by the Ba or Mg atoms, respectively, while compound 4 has infinite _∞(GeS₃)_n chains, which is different from the structures of the other three compounds that only have isolated MSe₄ (M = Sn, Ge) units. The measured IR and Raman data of the title compounds show wide infrared transmission ranges. The experimental band gaps of compounds 1, 2, and 3 were determined to be 1.79, 1.90, and 2.02 eV, respectively. Band structures were also calculated and indicate that their tetrahedral units, such as [SnSe₄], [GeS₄] and [GeSe₄], determine the energy band gaps of the title compounds, respectively. As for compound 1, based on fundamental light at 2.09 μm, the experimental second harmonic generation (SHG) response is about 1.6 times that of the benchmark AgGaS₂, which is also consistent with the calculated value. Based on the above results, compound 1 has promising applications in the IR field as a NLO material.