BaCdSnS4 and Ba3CdSn2S8: syntheses, structures, and non-linear optical and photoluminescence properties

Abstract

Two non-centrosymmetric metal chalcogenides, BaCdSnS₄ and Ba₃CdSn₂S₈, were synthesized using a high temperature solid-state reaction in an evacuated silica tube. Although the two compounds have the same building units in their structures, namely CdS₄, SnS₄ and BaS₈ units, both of them have different structures. BaCdSnS₄ crystallizes in the orthorhombic space group Fdd2 and its structure can be characterized by the two-dimensional _∞[Cd–Sn–S] layers composed of corner- and edge-sharing CdS₄ and SnS₄ tetrahedra with Ba atoms located between the two adjacent _∞[Cd–Sn–S] layers. Ba₃CdSn₂S₈ crystallizes in the space group I3d of the orthorhombic system and the CdS₄ and SnS₄ groups are connected with each other via corner-sharing to form a three-dimensional framework, which is different from the 2D _∞[Cd–Sn–S] layer structure in BaCdSnS₄. The UV-vis-NIR diffuse-reflectance spectra show that the experimental band gaps are about 2.30 eV for BaCdSnS₄ and 2.75 eV for Ba₃CdSn₂S₈, respectively. IR and Raman measurement results indicate that their transparent ranges are up to 25 μm. Second-order NLO measurements show that BaCdSnS₄ exhibits strong powder second-harmonic generation (SHG) intensities at 2.09 μm laser pumping that are ∼5 and 0.7 times that of AgGaS₂ in the particle size 38–55 and 150–200 μm, respectively, whereas Ba₃CdSn₂S₈ only exhibits SHG intensities of about 0.8 and 0.1 times that of AgGaS₂ at the same particle sizes. The origin of the NLO response in BaCdSnS₄ may originate from the macroscopic arrangement of the SnS₄ and CdS₄ tetrahedra. Furthermore, the photoluminescence properties of the two compounds have also been investigated and show obvious blue and green light emission.