Controlled Synthesis And Surface Modification Of Rare-Earth Doped Compound Fluoride Nanoparticles

Upconversion (UC) refers to nonlinear optical processes characterized by the successive absorption of two or more pump photons via intermediate energy states followed by the emission of the output radiation at a shorter wavelength than the pump wavelength. Rare-earth elements are17elements including lanthanides plus scandium and yttrium in periodic table. They mainly exist in their most stable oxidation state as trivalent ions. Rare-earth doped upconversion nanoparticles have unique optics, electronics and magnetic properties due to the4f-shell of rare-earth ions and nanomaterials’ surface effect, small size effect and quantum effect.In particular, upconversion emission from rare-earth doped nanoparticles offers an attractive optical labeling technique in biological studies without many of the constraints associated with organic fluorophores and quantum dots.(1) The upconversion technique utilizes near infrared (NIR) excitation rather than ultraviolet (UV) excitation, thereby significantly minimizing background autofluorescence, photobleaching, and photodamage to biological specimens.(2) The technique also allows in vivo observation with substantially high spatial resolution and offers remarkable sample penetration depths that are much higher than those obtained by UV excitation.(3) In addition, upconversion processes can be induced by a low power (1-103W/cm-2) continuous wave laser, as opposed to a costly high-intensity (106-109W/cm-2) pulse laser source for the generation of a simultaneous two-photon process. Among them, rare-earth doped compound fluoride nanoparticles attracted particular interest in optical labeling field due to their low phonon energy, low toxicity, high chemical stability and bright luminescence.In this article, we chooses NaYF4and NaGdF4as host materials, Yb3+, Er3+as sensitizer and activator, respectively. A variety of chemical techniques, including coprecipitation, thermal decomposition, hydro(solvo)thermal synthesis, sol-gel processing and combustion synthesis, have been demonstrated to synthesize rare-earth doped upconversion nanoparticles. The thermal decomposition method has proven useful for the synthesis of high quality, monodisperse, small-sized and strong luminescence rare-earth doped compound fluoride nanoparticles. Herein, we synthesized high-quality NaYF4and NaGdF4nanoparticles via the co-thermolysis of Na(CF3COO) and RE(CF3COO)3in oleic acid and1-octadecene. We obtained ligand-free nanoparticles using ligand oxidation method and reverse-microemulsion method to modify the hydrophobic nanoparticles.There are three parts in this paper:(1) Monodisperse, uniform and hollow structured hexagonal oleate-capped (3-NaYF4:Yb0.2Er0.02luminescent nanoparticles were synthesized by a facile one-pot thermal decomposition route. At the same time, ligand oxidation technique was utilized to render oleate-capped (3-NaYF4: Ybo.2Ero.o2nanoparticles water solubility.(2) A series of NaYF4:Ybo.2Er0.02nanoparticles were synthesized via the co-thermolysis of Na(CF3COO) and RE(CF3COO)3in oleic acid,1-octadecene at the reaction temperature of305℃. By tuning the ratio of Na/RE and reaction time, phase, shape, size, luminescence intensity and color of the nanoparticles can be manipulated.(3) High quality spherical NaGdF4:Yb0.2Ero.o2nanoparticles were synthesized via the co-thermolysis of Na(CF3COO) and RE(CF3COO)3in oleic acid,1-octadecene. Further, monodisperse and spherical core-shell structured NaGdF4:Ybo.2Ero.o2@SiO2nanoparticles were obtained by functionalization of spherical NaGdF4:Ybo.2Ero.o2nanoparticles with silica layers via a reverse-microemulsion process.