Controllable Synthesis, Characterization And Surface Modification Of Rare-earth Fluoride Luminescent Nanocrystals

Lanthanide-doped luminescent nanomaterials have great potentials in the fields of three-dimension displays, optical devices, biosensors and anti-counterfeiting applications. Particularly, the use of lanthanide-doped upconversion (UC) nanophosphors as biolabels for sensitive biological detection has attracted considerable interests due to their unique optical properties. Developing new synthetic technologies and related surface modification approaches for these luminescent nanomaterials is very important for both fundamental research and practical applications. In this thesis, explorations have been carried out on the controllable synthesis and surface modification of rare-earth fluoride luminescent nanocrystals (NCs).By using rare-earth trifluoroacetates as the precursors, lanthanide-doped LaF3 UC NCs with good crystallinity and regular hexagonal shape were prepared via a facile solvothermal strategy. The effects of experimental conditions on the morphology and structure of LaF3 NCs were investigated, and a reaction mechanism was proposed. Relatively slow crystallization rate was found to be the key factor for growing well-crystallized and regular-shaped LaF3 NCs. By co-doping different rare-earth ions for the LaF3 NCs, multicolor UC emissions can be realized, showing their potential applications as biolabels.A new synthetic method was developed to prepare monodisperse, uniform and well-crystallized lanthanide-doped NaGdF4 and LaF3 luminescent NCs by using simple NaF and rare-earth oleates as the precursors. The products could be controllably prepared with different morphologies, sizes and crystal structures. The role of oleic acid was found to be crucial for the NCs growth, and a monomer concentration-based principle was proposed to interpret the shape evolution of the NCs. By co-doping different rare-earth ions, the obtained NCs can exhibit intensive multicolor down-/up-conversion luminescence, which is promising for the applications of multiple biolabels. The results indicate that this work provides a new way for the preparation of high quality fluoride NCs.In high boiling organic solvents, a novel synthetic strategy was developed to prepare highly efficient UC luminescentβ-NaYF4:Yb,Er(Tm) nanospheres with small sizes. The as-synthesizedβ-NaYF4:Yb,Er(Tm) NCs are well suitable for biolabels because they show several advantages: small and tunable sizes that parallel to those of biomolecules (proteins or oligonucleotides), excellent size uniformity, and high UC luminescent efficiency. Surface modifications of the as-prepared hydrophobicβ-NaYF4:Yb,Er(Tm) nanospheres were performed to make them water dispersible, and at the same time, some functional groups such as free carboxylic acid groups were introduced onto their surfaces, which allowed further conjugation with biomolecules and paved the way for potential bio-applications of the UC nanospheres.