Abstract
The hexagonal phase NaYF4 (Na(Y1.5Na0.5)F6, β-NaYF4 type) is a kind of ideal host materials for upconversion luminescence with high efficiency. The synthesis of monophase hexagonal NaYF4:Yb3+/Er3+ nanoparticles has been investigated by solvothermal processing under 200° for 24hrs. It was found that solvents adopted had a great impact on formation of β-NaYF4. X-ray diffraction patterns indicated that monophase α-NaYF4 and β-NaYF4 nanosized grains could be synthesized successfully under environment of ethanol and oleic acid respectively, whereas the mixture of α-NaYF4 and Na5Y9F32 phases were obtained when water was used as solvent. The synthesized pure β-NaYF4 nanoparticles were uniformly monodispersed in hexagonal shape with typical length of 150~200nm and diameter of 50~100nm. Selected area electron diffraction observation revealed that the as-prepared nanorods are of single crystalline nature. By co-doping (20%)Yb-(2%)Er, the β-NaYF4 nanosized grains exhibited bright green upconversion luminescence centered at 538nm under the radiation of near-infrared (NIR) laser(nm). The FTIR spectrum shows theβ-NaYF4 have the potential of water-solubility for the strong bands at around 3444 and 1634 cm-1.
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