Elaboration, Structure and Luminescence of Sphere-Like CaF2:RE Sub-Microparticles by Ionic Liquids Based Hydrothermal...

A new and simple method for the synthesis of rare earth ion doped CaF₂ (CaF₂:RE³⁺) sub- microparticles is presented, using an ionic liquids based hydrothermal process. The structural properties of the CaF₂ nanoparticles were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CaF₂ nanoparticles exhibited a sphere-like morphology with a diameter of about 150 nm. During the synthesis, the ionic liquid [bmim]BF₄(1-butyl, 2-methylimidazolium tetrafluoroborate) acts as both a co-solvent and reactant. The crucial effect of EDTA-2Na (ethylene diamine tetra acetic acid disodium salt) on the formation of CaF₂:RE sub-microparticles was explored and discussed. The strong green (513-569 nm) and strong red (636-685 nm) upconversion emissions of the CaF₂:Er³⁺, Yb³⁺ nanoparticles (λex = 980 nm) were also investigated. The luminescent properties of CaF₂:Eu³⁺ and CaF₂:Ce³⁺,Tb³⁺ were also evaluated. This work may represent a new step in synthesizing fluoride sub-nanocrystals using ionic liquids.