Synthesis And Luminescence Properties Of Rare Earth Fluoride Nano/Microcrystals Via Ultrasound Assisted Ionic Liquid Method

Extensive use of traditional solvents has caused serious destruction of the environment, so the search for alternatives to the most damaging solvents has become an urgent issue. As a green solvent, ionic liquid has many unique properties, such as negligible vapor pressure, low toxicity, and high thermal stability and so on. Thus, it is an admirable replacement for traditional solvent. At present, ionic liquid has been widely applied in organic synthesis, catalysis, and electrochemistry, but the application of ionic liquid in inorganic nano/micromaterials is still in the initial stage. It is known that ultrasound irradiation of liquids caused by acoustic cavitation can generate transient high temperature and pressure, leading to high-energy chemistry. By combining the advantages of both ultrasound and ionic liquid, we have developed a simple, efficient and environment friendly method for synthesis of nano/micromaterials.In this paper, CeF3:Tb3+ nanodisks, LaF3:Tb3+nanoplates and microcylinders, and Na0.4iY0.59F2.18:Eu3+ microflowers have been synthesized via ultrasound assisted ionic liquid method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) were used to study the structures, morphologies and optical properties of as-obtained products.The CeF3:Tb3+ nanodisks that were prepared via sonochemical method crystallized well with hexagonal structure. The average diameter and thickness of CeF3:Tb3+ nanodisks are 450 nm and 80 nm, respectively. A comparative experiment under magnetic stirring instead of ultrasonic radiation proves that only nanoparticles could be obtained. And the possible formation mechanisms of CeF3:Tb3+ nanodisks and nanoparticles are also proposed. The emission intensity of the CeF3:Tb3+nanodisks increased significantly with respect to that of CeF3:Tb3+ nanoparticles under the same conditions. It showed that the luminescent properties of materials may be related to their different morphologies, sizes and surface defects, and so on.A series of hexagonal phase LaF3:yCe3+,xTb3+ nano/microcrystals were successfully synthesized via ultrasonic-assisted ionic liquid method. The SEM images revealed that the morphologies of the as-prepared LaF3:xTb3+ samples were gradually converted from nanoplates to microcylinders with increasing the concentration of Tb3+. Under the excitation of 254 nm, all the as-prepared LaF3:xTb3+ samples show the characteristic emissions of Tb3+ D4â†'7FJ (J=6,5,4,3) transitions. Meanwhile, the optimum doping concentrations of the LaF3:xTb3+ phosphors are investigated. In addition, the possible effect of the concentration of ionic liquid and Tb3+ on the samples’ morphologies is proposed in this paper. When the Tb3+ concentration was increased to 25 mol%, the transfer efficiency increased to 74.38%.By adding different concentrations of ethanol or ionic liquid, different sized Na0.41Y0.59F2.18 microflowers were successfully synthesized, and their possible formation mechanisms are also proposed. The flower-like Na0.41Y0.59F2.18:Eu3+ nanocrystals showed characteristic emission of Eu3+5Doâ†'7FJ (J=1-4) transitions, with the 5D0â†'7F1 magnetic dipole transition being the most prominent emission line.