Controlled hydrothermal growth and up-conversion emission of NaLnF4 (Ln = Y, Dy-Yb)

The controlled hydrothermal preparation of NaYF4 as both cubic and hexagonal phase types with specific associated morphologies, nanospheres and microtubes, respectively, has been achieved in the absence of organic solvents. The hexagonal NaYF4 compound can be prepared in novel microtubular form and directly co-doped with Yb3+/Er3+ ions. When excited by infrared light of 980 nm, these hexagonal NaYF4 microtubes display strong green up-conversion emission, which was much more intense than that of cubic NaYF4 or hexagonal NaYF4 nanoparticles. Other related hexagonal-prismatic microtubes of NaLnF(4) (Ln = Dy-Yb) were also synthesized. A growth mechanism for the microtubes is proposed. In general, the diameter of the hexagonal NaLnF(4) microtubes is strongly dependent on the Ln(3+) size and increases as the rare-earth ionic radius decreases.