Formation And Mechanisim Of Up-Converting Matrix Phosphors

Up-converting fluorescent nanocrystalline is a sort of material emits short wavelength light after excitated with long wavelength light. Most of them are attributed to inorganic material, for example, ytterbium and erbium co-doped yttrium fluoride, sodium yttrium fluoride, lanthanum fluoride, etc. Up-converting fluorescent material can emit different color visible fluorescence after excitated with 980 nm infrared light.Up-converting nanoparticles with few background and high detective sensitivity are a promising bio-molecule label. Until now, ytterbium and erbium co-doped sodium yttrium fluoride (NaYF₄: Yb, Er) is among the most efficient up-conversion phosphors. Its potential application in biological and medical fields has interested many scientists. As bio-molecule fluorescent labeling material, nanoparticles with small diameter, uniform distribution and strong luminescent intensity are necessary. Considering the application in practice, the size of the fluorescent nanoparticles was dominated by the original diameter of the matrix material. Therefore, if the smaller and uniform matrix nanoparticles could be synthesized, that should be significant for research of the material applied in bio-molecule label.Based on the similarity of rare earth elements, this work focus on studying the formation mechanism and reaction affecting factors of NaYF₄ nanoparticles without doping in aqueous phase, The obtained results are described as follows:(1) By investigating the effect of reactant time evolution and seeding effect for the formation of NaYF₄ particles, the result that NaYF₄ nanoparticles synthesized in aqueous grew in aggregation model, but not the typical LaMer model was concluded.(2) Reactant factors of reactant materials pH and chelators of EDTA for affecting the synthesis of NaYF₄ nanoparticles were studied. Y(ClO₄)₃ was helpful for getting smaller NaYF₄ particles than YCl₃ was found. Particles remained almost unchanged, when pH of the aqueous phase was in the range of 4-10. The molar ratio of chelators to yttrium and the amount of fluorin ion should be in a proper range so that small nanosized particles can be obtained. In this paper, under the condition of [EDTA] : [Y³⁺] = 1 and [NaF] = 0.5 mol/L, NaYF₄ of 30 nm was synthesized by Y(ClO₄)₃.(3) NaYF₄ nanocrystalline was prepared in the presence of chelators such as EDTA, Na-NTA, Na-Citrate. Nanoparticles of 12 nm were obtained by 0.12 mol /L Na-Citrate. Thereout, comparison of amino carboxyl chelating and hydroxy carboxylic chelating affecting the synthesis of NaYF₄ was studied.(4) Up-converting nanocrystal material of ytterbium and erbium co-doped sodium yttrium fluoride (NaYF₄: Yb, Er) with 10 nm was achieved in the presence of high concentrated Na-NTA.