Synthesis and characterization of fluoride xerogels.

Using coprecipitation from aqueous solutions, we have synthesized transparent fluoride xerogels with both hexagonal (NdF, PrF, and CeF; tysonite structure) and cubic (SrYF, BaYF:Bi, and BaYF:Yb; fluorite structure) symmetries. As shown by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, the transparent xerogels have a hierarchical structural organization: primary nanoparticles 20-30 nm in size form agglomerates about 100 nm in size, which in turn form a 'skeleton' with many voids and channels up to hundreds of nanometers in size. [ABSTRACT FROM AUTHOR]