Nonaqueous synthesis and selective crystallization of gallium sulfide clusters into three-dimensional photoluminescent superlattices.

A low-temperature, nonaqueous synthesis approach is described that produces a series of gallium sulfide and polysulfide three-dimensional superlattices from binary Ga-S and ternary Zn-Ga-S supertetrahedral clusters. The diversity of superlattices is achieved by modifying the cluster size, the cluster composition, and the inter-cluster linkage mode. Both pure T3 (Ga10S186-) (denoted as UCR-7GaS) and pure T4 (Zn4Ga16S3310-) (denoted as UCR-5ZnGaS) superlattices with ring sizes of 18 and 24 tetrahedral atoms have been made. Of particular interest is the synthesis of the T3-T4 hybrid superlattice (denoted as UCR-19) with an odd ring size of 21 tetrahedral atoms. Another unprecedented feature is the occurrence of the -S-S-S- polysulfide linkage between supertetrahedral clusters in UCR-18. The fluorescent emission wavelength of these materials ranges from 440 to 500 nm and fills the previously observed gap between open-framework oxides and indium sulfides. A comparative study shows that open-framework gallium sulfides are more thermally stable than indium sulfides. They can also undergo ion exchange. It is suggested here that supertetrahedral clusters of different types coexist in a solution and can be selectively crystallized out with a proper choice of structure-directing agents.