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.