Uniform NaYF4:Yb, Tm hexagonal submicroplates: Controlled synthesis and enhanced UV and blue upconversion luminescence

We reported the preparation of cubic (α-) and hexagonal (β-) NaYF4 particles in high boiling organic solvents 1-octadecene (ODE) and oleic acid (OA), through a thermal decomposition synthesis route. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL) spectra. By tuning the OA/ODE volume ratio and reactant concentration, we could manipulate the morphology, size, and crystal structure of the products. Highly uniform β-NaYF4 submicroplates were obtained from α-NaYF4 nanoparticles by increasing the OA/ODE volume ratio, while the phase kept unchanged with the increasing of reactant concentration. Upconversion emissions from UV to NIR emissions were observed in β-NaYF4 hexagonal submicroplates under 980 nm laser diode excitation. In addition, the enhanced UV and blue upconversion emissions were obtained by varying Tm3+ and Yb3+ ion concentration.

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► β-NaYF4 phosphors as an excellent upconversion materials.
► Oleic acid can promote the transformation of α → β phase NaYF4.
► The shape and size of β-NaYF4 submicroplate can be tuned by reactant concentration.
► Enhanced UV and blue peaks can be obtained by varying Yb3+ and Tm3+ concentration.