The Preparation And Properties Of Lanthanide-doped Fluoride Nanocrystals

In this paper, the synthesis process and luminescence properties of Ce³⁺, Ln³⁺ (Ln=Tb, Dy, Eu and Sm) co-doped GdF₃ nanocrystals, Eu³⁺ doped NaGdF₄ nanocrystals and Yb³⁺, Ln³⁺(Ln=Er, Tm) co-doped LaF₃ upconversion nanocrystals were investigated. The effect of doped rare earth ions types, synthesis process and heat treatment temperatures were systematically investigated by using X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL) spectra.Ce³⁺, Ln³⁺ (Ln=Tb, Dy, Eu and Sm) co-doped GdF₃ nanocrystals were synthesized by co-precipitation method. Multicolor emissions were achieved by using 250nm light as excitation source. Such multicolor emissions could be used as multicolor bio-label technology in future. The energy transfer efficiencies between Ce³⁺ ions and Tb³⁺ ions, Dy³⁺ ions, Eu³⁺ ions are relatively higher than that between Ce³⁺ ions and Sm³⁺ ions.Eu³⁺ doped NaGdF₄ crystals were synthesized by using hydrothermal methods. The effects of different NaF ratios (100%, 105%, 110%, 115% and 120%) as start materials and different synthesis temperatures (100℃, 120℃, 140℃, 160℃, 180℃, 200℃and 220℃) on the crystal structures, morphology and photoluminescence intensities were investigated. The intensity of ⁵Do→⁷F₂ transition of Eu³⁺ ions was closely related with the amount of GdF₃ phase. The reduction of GdF₃ phase and increase of NaGdF₄ could substantially enhance the intensity of ⁵Do→⁷F₂ transition.Yb³⁺ and Ln³⁺ (Ln=Er, Tm) co-doped LaF₃ nanocrystals were synthesized by co-precipitation method. The effects of different heat treatment temperatures on crystal structure, morphology and photoluminescence intensities were investigated. The upconversion intensities increased with increase of heat treatment temperatures, but the colloid properties of LaF₃ nanocrystals would be destroyed at 600℃. Using the relationship of pump power and upconversion emission intensity, the upconversion mechanism was confirmed.