Synthesis, structures, optical properties and electronic structures of PbGa2Q4 (Q = S, Se) crystals

• Different structures between titled crystals were determined.
• Theoretical calculations were performed to understand the electronic structure.
• Optical band gaps calculated are consistent with experimental values.
• Birefringences simulated by the DFT method are close to 0.1 around 1 μm.

Single crystals of PbGa2Q4 (Q = S, Se) have been successfully synthesized by solid-state reactions and their structures are determined by single-crystal X-ray diffraction methods. They are isostructural and crystallize in the orthorhombic space group Fddd (Z = 32). In their crystal structures, the GaS4 or GaSe4 units are connected with corner or edges sharing to form layers, and these layers are bridged by Pb atoms to generate a three-dimensional (3D) framework. The UV–Vis–IR diffuse reflectance spectra exhibit that the optical band gaps are about 2.38 and 1.83 eV for PbGa2S4 and PbGa2Se4, respectively, which are consistent with the calculated values. Their thermal behaviors and Raman spectra were also measured. First-principle theoretical studies are used to aid the understanding of electronic structures and linear optical properties.

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