Uniform core-shell structure Fluoride Nanocrystals with up-conversion luminescence

Title: Uniform core-shell structure Fluoride Nanocrystals with up-conversion luminescence
　　Author: Liu Lixin
　　Degree-granting unit: Harbin Institute of Technology
　　Keywords: fluoride nanocrystals;; synthesis;; core-shell structure;; fluorescence enhancement
　　Summary:
　　In recent decades, rare-earth doped upconversion nanocrystals as interference from tissue autofluorescence, deep tissue penetration depth of the advantages of fluorescent markers in biological and bio-imaging has great potential for application. Shape-controlled preparation of nanocrystalline and improve its conversion efficiency to be studied, so this paper to Neodymium magnets study the mono-dispersed, small, uniform particle size, shape rules of rare-earth doped NaYF_4 synthesis of nanocrystals and core-shell structures by improving The upconversion efficiency of the work started two aspects.
　　By hydrothermal method and thermal methods of oil were prepared NaGdF_4: Yb20%, Ho2% and NaYF_4: Yb 20%, Er, Tm2% cubic nanocrystals. On this basis, were prepared with different core-shell structure shell nanocrystals NaGdF_4: Yb20%, Ho2% / NaY_xGd_ (1-x) F_4 (x = 0,0.5,0.8,1) and NaYF_4: Yb 20%, Er, Tm2% / NaY_xYb_ (1-x) F_4 (x = 0,0.3,0.6,1). Conversion by detecting the fluorescence spectra of core-shell structure of nanocrystals that can reduce the activation of non-radiative relaxation process of ions with higher luminous efficiency. Discussed the shell Gd ~ (3 +) or Yb ~ (3 +) ions doping concentration on luminescence efficiency.
　　Improved a simple, economical, environmentally friendly hot solvent synthesis. Controlled by changing the reaction time and surfactant oleic acid doping prepared monodisperse, small size, particle size uniformity, different shapes of NaYF_4: Yb20%, Er2% hexagonal nanocrystals. Observed by transmission electron micrograph morphology of the sample found in the reaction time under the same conditions, the doping concentration of surfactant the larger nanocrystals become more rounded morphology and slower growth.
　　Using the above solvents were prepared by hot-monodisperse, shell thickness of NaYF_4: Yb20%, Er2% / NaY_xYb_ (1-x) F_4 (x = 0,1) core-shell structure of nanocrystals. Tested on the conversion and time-resolved fluorescence spectroscopy and http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php found that the cladding around the nanocrystals branching ratio spectrum changes, and compared with the bare nanocrystalline core, core-shell structure of nanocrystals of the infrared energy levels about 1.5 times longer life, analysis that core-shell structure has been successfully reduced by non-radiation relaxation process, improves the conversion efficiency. And the shell of the sensitizer Yb ~ (3 +) ions can activate the role of the nucleus of the ion, and further improve its conversion efficiency.
　　Degree Year: 2010