Dicarboxylate mediated efficient morphology/phase tailoring of YPO4:Ln3+ crystals and investigation of down-/up-conversion luminescence

The dicarboxylate anions of tartrate (C4H4O62-, Tar(2-)), malate (C4H4O52-, Mal(2-)), and succinate (C4H4O42-, Suc(2-)) were originally used as morphology/structure modifiers in the hydrothermal crystallization of YPO4, and both hexagonal (h-) and tetragonal (t-) structured crystals with multiform morphologies of high uniformity were selectively synthesized. The materials were characterized by the combined techniques of XRD, FE-SEM, TEM, FT-IR, TG, and optical spectroscopy, and the mechanisms of phase/morphology evolution were expatiated. It was clearly shown that Tar(2-) may induce an inverse phase transformation of YPO4 from the thermodynamically stable tetragonal structure (nanoparticles) to the metastable hexagonal structure (microprisms), and a series of controlled experiments exhibited that the performance of Tar(2-) was strongly affected by the experimental parameters of Tar(2-)/PO43-/Y3+ molar ratio, solution pH, hydrothermal temperature, and reaction time. In comparison with Tar(2-), Mal(2-) induced the direct crystallization of h-YPO4 microprismatic crystals while Suc(2-) restricted the 1-D growth of t-YPO4 nanocrystals. For the samples calcined at 700 degrees C, the down-conversion photoluminescence of Eu3+ in h-YPO4 and t-YPO4 and the up-conversion luminescence of the (Yb/Er)(3+) couple in t-YPO4 were also comparatively studied and elucidated in detail.