Controlled synthesis of β-NaYF4:Yb, Er microphosphors and upconversion luminescence property

NaYF4:Yb3+/Er3+ with different phases, morphologies, and luminescent properties were synthesized using a facial hydrothermal method. The as-obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) pattern, and photoluminescence (PL). The XRD results indicated that ethylene diamine tetraacetic acid (EDTA) and citrate play an important role in phase transition at low reaction temperatures. SEM images revealed that samples morphologies can be changed from irregular shapes to regular microprisms by EDTA and citrate. TEM images showed that the diameter of samples synthesized at 120 °C without any chelating agents is ∼50 nm. HRTEM indicated that the crystal grows along the [111] plane. The selected area electron diffraction (SAED) pattern showed that the nanoparticles have a good single-crystalline structure. FL spectra revealed that citrate can reduce the luminescence intensity at any reaction temperature. However, EDTA can improve optical properties at low reaction temperatures.