Synthesis and characterization of mid-infrared transparency compounds: acentric BaHgS2 and centric Ba8Hg4S5Se7.

Two mid-IR transparency compounds, namely, acentric BaHgS2 (BHS) and centric Ba8Hg4S5Se7 (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic Pmc21 with [HgS4] tetrahedra and isolated dumbbell-shaped [HgS2] units, while BHSSe belongs to the orthorhombic space group Pnma with infinite isolated ∞[HgSe2(S/Se)2](4-) chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ∼6.5 times compared with that of reference AgGaS2 at a fundamental wavelength (2.09 μm). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation.