K2ZnGe3S8: A Congruent-Melting Infrared Nonlinear-Optical Material with a Large Band Gap

• Published in: Inorganic chemistry 2018-08, Vol.57 (15), p.9446-9452
• Main Authors: Luo, Xiaoyu, Liang, Fei, Zhou, Molin, Guo, Yangwu, Li, Zhuang, Lin, Zheshuai, Yao, Jiyong, Wu, Yicheng
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b01437

K2ZnGe3S8 belonging to the noncentrosymmetric space group P21 of the monoclinic system was discovered via a solid-state method. It possesses two-dimensional [ZnGe3S8]2– layers, with alkali-metal cations K+ located between the layers. On the basis of UV–vis–near-IR diffuse-reflectance spectrometry, the band gap of K2ZnGe3S8 is 3.36(2) eV. According to powder second-harmonic-generation (SHG) measurements, the SHG response of K2ZnGe3S8 is about 0.9 times that of AgGaS2 at the particle size range of 20–41 μm. Experimental results demonstrate that K2ZnGe3S8 keeps a good balance between a large band gap (3.36 eV) and a moderate SHG response. Moreover, according to the differential scanning calorimetry measurements, K2ZnGe3S8 melts congruently at around 1023 K and recrystallizes at about 963 K. Therefore, it is possible to obtain bulk single crystals via the Bridgman–Stockbarger method. The first-principles calculations indicate that the optical properties of K2ZnGe3S8 are dominantly determined by the [GeS4] tetrahedra as well as a small contribution from the [ZnS4] tetrahedra.