Title: Employing dicarboxylic acids in the KF-YF3 system to modulate the crystal phase and optical response of Eu3+-doped materials

Abstract

Among many inorganic materials, fluorides are the most appealing candidates for optical applications because of their low phonon energy associated with the crystal lattice. The compounds of the KF-YF3 system (particularly YF3 and KY3F10) doped with Ln3+ ions have shown outstanding optical response during the last years. Although Ln3+-doped fluorides have been prepared in the literature with different capping agents that allow their surface modification, no attempts have been made to prove whether the use of dicarboxylic ligands in the KF-YF3 system can be successful or not. Based on the aforementioned points, Eu3+-doped YF3 and KY3F10 materials were prepared hydrothermally in a wide range of pH values without the use of surface chelators and adding oxalic or tartaric acid using KBF4 as the fluoride source. It has been proved for the first time the effective use of dicarboxylic ligands as chelating agents to modulate the surface and thus the crystal phase evolution in the KF-YF3 system. The morphologies and crystal structures of the materials displayed a critical dependence on the pH and the dicarboxylic acid used. Consequently, the materials exhibited a modulated optical response: orangish-yellow emissions, high quantum efficiencies (65–133 %), and very long lifetimes (7–12 ms). The calculation of the Judd-Ofelt parameters also allowed to establish a relationship between the physicochemical properties of the phosphors and their luminescence. The above novel strategy could arouse widespread interest since it could also be applied to a vast gamut of compounds from the extended family of yttrium/lanthanide fluorides and find interesting applications in bioanalytics, photonics, or white light-emitting diodes.