Facile Ionic Liquid-Assisted Strategy for Direct Precipitation of Eu2+ -Activated Nanophosphors under Ambient Conditions

Abstract

This work describes a novel ionic liquid (IL)-assisted synthesis strategy for a direct and easy production of Eu²⁺ -doped nanoparticles (NPs), where ILs are also used as fluoride sources to avoid the use of elemental fluorine or toxic hydrofluoric acid. Up to now, the direct synthesis of Eu²⁺ -doped nanophosphors consisted of an enormous challenge, due to the oxidation to Eu³⁺ observed in hydrous solution, which is commonly used for the preparation of NPs, generating lattice defects and undesired particle growth or agglomeration by additional reducing steps at high temperatures. In contrast, ILs, unless containing ClO₄^- or NO₃^- anions, do not present an oxidizing character, allowing the direct precipitation of NPs, e.g., using Eu²⁺ containing starting materials. Here, the undoped and Eu²⁺ -doped BaFCl NPs have been prepared under atmospheric conditions for the first time using ILs as solvents and also as fluoride source, applying sonochemical and microwave-assisted approaches. In general, this method bears an enormous potential for an easy synthesis of fluoride materials compared to inconvenient solid-state methods. In addition, the IL plays the role of a strongly attached protecting shell which represents ≈7-8% of the total NPs weight.

Keywords: divalent europium; ionic liquids; microwave chemistry; nanoparticles; sonochemistry.