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

A new and simple method for the synthesis of rare earth ion doped CaF₂ (CaF₂:RE³⁺) submicroparticles 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 (λ_ex = 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.