Multicolor Tuning And Properties Of Rare Earth Fluoride Upconversion Nanomaterials

Due to their special upconversion luminescence performance, superior chemical and physiological properties, rare earth fluoride upconversion nanomaterials with multicolor output had been widely used in the fields of multicolor display, photonic devices, biomedical etc. In this thesis, we developed several new general protocols for the fine-tuning multicolor output of fluoride upconversion nanomaterials, based on changing the nonradiative relaxation probability of lanthanide luminescent ions, by controlling surface ligands, internal defects and crystallinity, and phonon energy, respectively.A general approach for the multicolor fine-tuning of fluoride upconversion nanoparticles (UCNPs) was developed by simply controlling the composition of two ligands during the synthesis procedure. The interaction between oleic acid (OA) and octadecylamine (OM) in reaction system and the surface ligands of nanoparticles were monitored and analyzed by1H-NMR and FT-IR spectroscopy. It is revealved that OA reacted with OM to form N-octadecyloleamide (OOA) before nucleation of fluoride nanoparticles. With the variation of OA/OM in reaction solution, the relative content of OOA molecule in the surface ligands was varied, which resulted in the multicolor output of NaYF4:Yb, Er nanoparticles with red, orange, yellow, yellow-green, green. This approach was not only expanded to the multicolor tuning of Ho3+and Tm3+, but also to the different host matrix (e.g. NaGdF4and NaLuF4) and ligand pairs (e.g. octadecylamine and oleamide).A new approach for the multicolor tuning of fluoride UCNPs was designed and testified based on controlling the crystallinity through tuning reaction temperature and time. The effects of reaction temperature and time on the internal defects and crystallinity were investigated, and it was demonstrated that the variation of crystallinity induced the multicolor emissions of nanoparticles through the control experiments, XRD, HR-TEM, and calculated results of Williamson-Hall methodology. Similarly, this method could also achieve the multicolor tuning of NaYF4:Yb,Ho and NaYF4:Yb,Tm UCNPs.A general new approach for the multicolor tuning of fluoride UCNPs was designed and testified by controlling phonon energy, which was achieved through tuning the relative content of oxygen impurities by changing the addition amount of NH4NO3. Upconvesion spectroscopy, X-ray fluorescence spectroscopy, Raman spectroscopy, and upconversion mechanism demonstrated the rationality of this strategy. In addition, the effects of addition temperature of NH4NO3and other oxygen sources on the upconversion luminescent performance were investigated. It is revealed that NH4NO3could be used as the oxygen source, and should be added into the reaction solution when the temperature was raised to250℃to achieve the effective multicolor tuning of fluoride UCNPs. This method could also be used for the multicolor tuning of Ho3+ion and Er3+ion in the host matrix of NaYF4and NaLuF4. Subsequently, as-prepared UCNPs were incorporated into the organic polymer and used as the color converters for LEDs with excellent performance, which could effectively convert the infrared light into visible ones, and these UCNPs exhibited great potential applications in many areas.