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K2HgGe3Se8: A Quaternary Hg-Based Selenide with Nonlinear Optical Properties

Guili Wang,Pifu Gong,Jiyong Yao

A new quaternary Hg-based selenide K2HgGe3Se8 was successfully synthesized and characterized as an engaging infrared (IR) nonlinear optical (NLO) material, which crystallizes in the P21 space group of the noncentrosymmetric monoclinic crystal system. The crystal structure of K2HgGe3Se8 is characterized by the stacking of countless [HgGe3Se8]2−2∞${}_{\infty }{}^2{[\mathrm{H}\mathrm{g}{\mathrm{G}\mathrm{e}}_3{\mathrm{S}\mathrm{e}}_8]}^{2-}$ layers with K+ cations filling the interlayers. The UV–vis–NIR diffuse reflectance spectrum shows that K2HgGe3Se8 possesses an indirect band gap of 2.13 eV. The second harmonic generation (SHG) response of K2HgGe3Se8 is approximately 1.1 times that of AgGaS2 (AGS) within the particle size of 20–50 μm along with a nonphase-matching (NPM) behavior at 2090 nm, as indicated by the SHG test. K2HgGe3Se8 also has a large powder laser-induced damage threshold (∼ 2.3 × AGS). As revealed by theoretical calculations, the optical properties of K2HgGe3Se8 are predominantly determined by [HgSe4] and [GeSe4] tetrahedra, and K2HgGe3Se8 possesses a calculated optical band gap of 1.44 eV together with a maximum SHG coefficient d22 of −7.70 pm V–1.