Synthesis And Upconversion Luminescent Properties Of Rare-Earth-Doped NaYF₄Nanocrystals

In recent years. Rare-earth-doped NaYF4have attracted considerable attention owning to their superior chemical and optical properties, such as low phonon energy, narrow emission peaks (<10nm), long lifetimes (us-ms range), large anti-stokes shifts, excellent luminescence properties and low toxicity. Ln3+binary doped NaYF4nanostructures have been regarded as the most commonly-used UC luminescent host materials and thus have been widely studied ranging from their synthetic strategies to their potential biological applications.In this paper, the high light-emitting efficiency, morphology controlled. and small nanoparticles was successfully prepared by a simple hydrothermal method, these products would be extended to use in biological sensing applications.The thesis can be divided into three parts:In the first part, the spherical, about100-200nm and single crystalline phase of the NaYF4:Yb/Er nanomaterials were successfully synthesized by the hydrothermal method. Then the crystalline phase, morphology and size of the product can be adjusted by changing the amount of fluorine source. We have successfully synthesized beautifully spherical product by adding EDTA, which can limit the anisotropic of crystal growth by complexation reactions.In the second part, an interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4: Yb/Er upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of20nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at980nm. In addition. because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.In the third part, Ln-doped NaYF4nanocrystals were successfully synthesized by combining a stable microemulsion and the hydrothermal method. This strategy can synthesize single-dispersion, high yield, small size, pure hexagonal phase upconversion luminescent nanocrystal through an improved reaction conditions, varying the reaction parameters. And mechanism, which controls nanocrystals in small size and hexagonal phase, were discussed in thermodynamics (diffusion-controlled growth" and "organic-inorganic interface effect") and the dynamics.