Effect of reactants concentration on NaYF₄:Yb³⁺, Tm³⁺ crystalline phase

A series of NaYF₄:20%Yb³⁺, 1%Tm³⁺ upconversion particles (UCPs) with different morphology were prepared by the facile hydrothermal approach. The morphology, crystalline phase and optical properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and luminescent spectra. XRD patterns and SEM images showed that the UCPs crystalline phase tansformed from cubic phase to hexagonal phase by controlling the reactants concentration. Pumped with 980 nm diode laser, the UCPs emitted bright violet/blue upconversion luminescence. By analyzing the effect of reactants concentration on the products crystalline phase, the crystal growth mechanism of NaYF₄ was studied in detail. Significantly, our research work would provide more experimental data for controlling the crystalline phase of the upconversion luminescent materials.