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Preparation and fluorescence properties of nanocomposite fluoride

Author: GuoJianChen
Tutor: ZengJingHui
School: Shaanxi Normal University
Course: Inorganic Chemistry
Keywords: inorganic single-source precursor green synthesis hydrothermal method complex fluoride nanomaterials
CLC: TB383.1
Type: Master's thesis
Year: 2008
Downloads: 138
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Abstract

It still remains an open challenge to identify a suitable synthetic route for growing high-quality （monodisperse, single-crystalline, wellshaped, and phase-pure） products of a given inorganic material. Herein, we report the first synthesis of monodisperse nanocrystallines of hexagonal phase NaYF₄ and YOF via a non-toxic inorganic single-source precursor NaY（CO₃）F₂ route.In present work, different reaction parameters such as solvent, reaction time and temperature were studied for the phase, size, and morphology control of the precursor and product nanocrystallines. Both Eu³⁺ doped NaYF₄ and YOF can be synthesized using the same ISSP, NaY（CO₃）F₂: Eu³⁺, by hydrothermal and heat treatment respectively. When the precursor was treated hydrothermally at 230℃for 10 h, hexagonal phase NaYF₄: Eu³⁺ nanocrystallines were prepared. When the precursor was pyrolyzed at 400℃for 1 h in air atmosphere, YOF: Eu³⁺ nanocrystallites were the final product. The products were measured by means of XRD, SEM, TEM, Photoluminescent spectra. The results are shown that , the NaYF₄: Eu³⁺ and YOF: Eu³⁺ particles possesses high purity, sphere-like shape, nano size, excellent nanodispersity. The size of NaYF₄: Eu³⁺ was about 20 nm while that of YOF: Eu³⁺ is little larger, about 30 nm, which may be related to the crystal growth under elevated temperatures. Eu³⁺-doped NaYF₄ and YOF nanocrystallines were used for the photoluminescence examinations. Intense red luminescent light was observed for Eu³⁺ doped NaYF₄ and YOF nanocrystallines excited at 245 nm at room temperature.The thermal decomposition of rare earth fluorocarbonate can be extended to prepare other rare earth complex fluoride and oxyfluoride and will have a good morphology features. When the inorganic single-source precursor Yb³⁺/ Er³⁺ co-doped LaCO₃F was pyrolyzed at 460℃for 2 h in air atmosphere, LaOF:Yb³⁺/ Er³⁺ nanocrystallites were the final product. The broad diffraction peaks of the XRD pattern showed the product to be of the nanometric size regime with high purity. The TEM images showed the size of LaOF: Yb³⁺/ Er³⁺ particles were close to spherical particles with the size about 40 nm. Excited with a 980 nm laser sourc, intense upconversion luminecense was observed for LaOF: Yb³⁺/ Er³⁺ particles at room temperature using the naked eye. The thermal decomposition of rare earth fluorocarbonate is a facile nontoxic synthetic route for the preparation of complex fluoride and oxyfluoride nanocrystallines. Other rare earth or transition metal complex fluorides and oxyfluorides may also be synthesized using the present technique. In a typical procedure, NaYF₄ was synthesized by hydrothermal reaction of metal nitrates and NaF at 200℃for 12 h. The product is amixture of the cubic phase and the hexagonal phase NaYF₄ with the n（F）/ n(Y³⁺) ratio is 6. It is beneficial to the transformation from cubic phase to the hexagonal phase NaYF₄ when improving stirring speed or adding a certain quantity of Na₂CO₃（1 mmol）. When the n（F）/ n(Y³⁺) ratio is 9, the pure hexagonal phase NaYF₄ with rodlike structures can be obtained easily.A series of NaYF₄: Yb³⁺/ Er³⁺, NaYF₄: Yb³⁺/ Tm³⁺, NaYF₄: Yb³⁺/ Er³⁺/ Tm³⁺, NaYF₄: Yb³⁺/ Er³⁺/ Mn²⁺ samples were synthesized by hydrothermal method. The green-red emissions were generated by NaYF₄: Yb³⁺/ Er³⁺ phosphor. The experimental results indicate that the upconversion（UC） green light decreased obviously compared with the variation of red light when increasing amount of Mn²⁺ ion. The optimum color ratio was tuned by Mn²⁺ doping cation. The blue emission was from NaYF₄:Yb³⁺/ Tm³⁺ phosphor. Bright upconversion white light was observed by the combination of NaYF₄: Yb³⁺ 20 %, Er³⁺2 %, Mn²⁺ 50 % green-red phosphor and NaYF₄: Yb³⁺ 20 %, Tm³⁺ 0.2 % blue phosphor.

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