“…However, stable growth of the perfect ZGP crystal with high optical quality is very difficult due to the physical and chemical properties of this material. Firstly, ZGP is a complex ternary system, and contains two volatile components, Zn and P, with high vapor pressure at the melting temperature of 1027 1C, which can result in component deviations from stoichiometry not only in the process of polycrystalline synthesis but also in the growth process of ZGP single crystal; deviations from stoichiometry can lead to the formation of large magnitude of point defects, such as zinc vacancy (V Zn ), phosphorus vacancy (V P ) and Ge-Zn substitutional defect (Ge Zn ), which mainly result in high optical absorption in the range of 0.65-2.5 mm as mentioned in some literatures [1,3,[7][8][9][10][11][12]. Secondly, the vapor pressure of phosphorus is very high above its melting point.…”