Accessing Mixed-Halide Upconverters Using Heterohaloacetate Precursors

A new type of organic–inorganic hybrid precursor to mixed-halide optical materials is described by using Ba5(CF2ClCOO)10·7H2O as an example. This heterohaloacetate belongs to the family of extended inorganic hybrids in which metal connectivity in three dimensions is achieved via metal–organooxygen–metal bridges. Thermolysis in the solid state and in solution yield crystalline BaFCl at temperatures below 300 °C. Chlorodifluoromethyl groups act as chlorine and fluorine source, making the organic moiety a de facto single-source precursor for the anionic portion of the target mixed halide. Solution thermolysis in the presence of Yb3+–Er3+ sensitizing–activator pairs yields rare-earth-doped BaFCl nanocrystals capable of NIR-to-visible photon upconversion. Analyses of the composition, morphology, structure, and luminescence of these nanocrystals demonstrate that heterohalocetates serve as dual halogen sources for mixed-halide optical materials. Findings presented in this article enlarge the synthetic toolbox to access mixed halides at temperatures compatible with solution synthesis and processing.