NEW SYNTHESES OF LUMINESCENT MATERIALS FROM IONIC LIQUIDS

Abstract

The scope of my work was to improve the luminescence from rare earth doped compounds by optimization of synthesis routes for the known materials or investigation of new efficient luminescent materials. As an early stage researcher (ESR5) in the LUMINET project (Marie Curie Fellowship Program) in “Luminescent Nanopowders”, I devoted most of my work to the syntheses of nanoparticles doped with lanthanides. Their unique properties as emitting materials were deeply investigated and new syntheses were proposed for β-NaGdF4: Ln3+ and TiO2: Ln3+, see Chapter 3 and 4, respectively. The lanthanides used in this work are Eu3+, Er3+, Yb3+, and Sm3+. The syntheses of luminescent nanoparticles were accomplished by room temperature synthesis in ethylene glycol for β-NaGdF4: Eu3+, Er3+ in Section 3.2, and microwave-assisted heating from ionic liquids for β-NaGdF4: 18% Yb3+, 2% Er3+ and TiO2: Eu3+, Sm3+ in Sections 3.3 and 4.2, respectively. The latter method allows for the synthesis of efficient luminescent nanoparticles in anhydrous conditions due to the low vapour pressure of the ionic liquids. It corresponds to a distinct advantage over the common synthesis methods due to the luminescence quenching from the water molecules. Diallyldimethylammonium-based ionic liquids were used in this work, which bear a polymerizable cation. This allows to yield luminescent nanocomposites in an one-pot synthesis, see Section 4.2. The synthesis in ionic liquids leads to sub-10 nm luminescence nanoparticles, whose luminescence is more efficient with respect to those synthesized in other solvents. It is particularly of advantage for β-NaGdF4: 18% Yb3+, 2% Er3 + upconversion luminescence nanoparticles, whose efficiency is already orders of magnitude lower than the bulk material. The synthesis was accomplished at low temperatures with respect to protocols in the literature and within 5 minutes, which further constitutes an improvement. Core-shell nanoparticles were also achieved in one-pot synthesis, which reduces the number of impurities and yield higher efficient luminescence from β-NaGdF4: 18% Yb3+, 2% Er3+ nanoparticles. Functionalization of upconversion nanoparticles surface was achieved with watersoluble compounds, see Section 3.3. This step is required for application of the upconversion nanoparticles in biological imaging. Folate-capped nanoparticles were also synthesized for applications in targeting and imaging of cancer cells. Finally, new titanium-based hybrid materials were produced from a sol-gel route, see Section 4.3. The luminescence of Eu3+-doped materials was investigated and the influence of ionic liquids on the syntheses was reported. The luminescent materials were characterized with respect to their phase purity, luminescence, and size by powder X-ray diffraction, luminescence spectroscopy, and electron microscopy, respectively. Nuclear magnetic resonance, Fourier transform infrared, and thermal analyses were further used for the characterization of the organic ligands. The valuable results achieved benefit from user-friendly and scalable synthesis routes, which can be easily extended to the whole lanthanide series.