【摘要】 利用X射线多晶衍射仪、场发射扫描电镜、场发射透射电镜、X射线光电子能谱和荧光光谱仪对相近半径离子Hf⁴⁺和Zr⁴⁺共掺六方Na YF₄:Yb³⁺/Tm³⁺的结构、形貌和上转换发光性能进行研究.结果表明Hf⁴⁺和Zr⁴⁺离子共掺六方Na YF₄:Yb³⁺/Tm³⁺可有效调控晶场的不对称性,Hf⁴⁺相对于Zr⁴⁺是个更好的掺杂离子,它在调控晶场的同时还参与Tm³⁺离子上转换发光的能量传递过程,明显提高了短波500 nm以下发射带的荧光强度;而Zr4+离子仅扮演晶场调控角色而未能参与稀土离子Tm³⁺的上转换发光过程,Tm³⁺离子小于500 nm短波发射带的荧光强度没有得到明显的提高,仅提高802 nm发射带的荧光强度.该研究发现Hf⁴⁺可作为蓄能离子参与稀土离子的上转换发光过程,有助于将Hf⁴⁺作为蓄能离子和晶格操纵工具用于设计和制备其它高性能的稀土上转换发光材料.更多还原

【Abstract】 In this paper we report the infrared to visible upconversion（UC） luminescence properties of Hf⁴⁺ and Zr⁴⁺codoped Na YF4: Yb³⁺/Tm³⁺. Samples were synthesised by hydrothermal method. Concentration of Tm³⁺ and Yb³⁺ ions were fixed to be 2 mol% and 5 mol% for all samples, respectively. Na Y0.93-xYb0.05Tm0.02F4 was tridoped with 0, 2, 4, 6, 8 mol% Hf⁴⁺ or Zr⁴⁺ and corresponding samples were named as Hf0, Hf2, Hf4, Hf6, Hf8 and Zr0, Zr2, Zr4, Zr6, Zr8, respectively. In a typical procedure, trivalent nitrate stock solutions of 0.2 mol/L were prepared at first by dissolving the corresponding metal oxide in concentrated nitric acid or hydrofluoric acid at elevated temperatures. And then, a certain mole percentage of trivalent nitrate solutions were added into 20 m L 0.04 mmol EDTA aqueous solution. After vigorous stirring for 30 min, 25 m L ethanol solution containing 0.2 mmol Na F, 0.2 mmol NH4HF2 and corresponding stoichiometric amount Hf⁴⁺ or Zr⁴⁺ were dropwise added into the solution, and then p H value of solution was adjusted to 3.0 by addition 1 mol/L HF, and stirring continued for 30 min. Then the emulsion mixture was moved to PTFE-lined high pressure pot and incubated in oven at 180 ℃ for 12 h. The final products were collected, washed several times with water and ethanol alternately, and gathered by centrifugation, and then dried in oven at 60 ℃. Crystal microstructure, morphology and UC luminescence properties of samples were investigated by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and upconversion photoluminescence spectra. Results revealed the bond distance of F1-Y and F2-Y become close with the rising of Hf⁴⁺ or Zr⁴⁺ codoped concentration, indicating crystal field asymmetry of rare earth ions were tuned effectively by Hf⁴⁺ or Zr⁴⁺ codoping. Electron hypersensitive transition was promoted, and the intensity of 802 nm emission was enhanced obviously. Hf⁴⁺ ion was a better dopant than Zr⁴⁺, for the extranuclear electronic structure of Hf⁴⁺ was the same with rare earth ions, and Hf⁴⁺ ion was involved in UC process as a migrator to improve Tm³⁺ upper state levels’ population. UC luminescence of Hf⁴⁺ codoped sample were enhanced obviously, especially the shortwave emissions. The reported work establishes the understanding of Hf⁴⁺ as a migrator for Tm³⁺ ions upconversion luminescence, which may be helpful for design and synthesis of high-performance upconversion materials.更多还原