Development of Upconversion Phosphors with Three Primary Colors Based on Rare-Earth Doped Solid Compounds

Development of Upconversion Phosphors with Three Primary Colors Based on Rare-Earth Doped Solid Compounds
　　In this thesis, several kinds of phosphors were synthesized via solid-state reaction method, including rare earth ion Er3+/Yb3+ co-doped sodium yttrium fluoride based green emitting upconversion phosphor, Tm3+/Yb3+ co-doped sodium yttrium fluoride based blue emitting upconversion phosphor, Er3+/Yb3+ co-doped YOCl and YOF based red emitting upconversion phosphor. It was systematically discussed for the effect of rare earth ion concentration, the chemical structure of the host lattices, heating temperature and holding time on the luminescent properties.A kind of upconversion phosphor for 980nm LD exciting in which pure hexagonal NaYF4:Er3+/Yb3+ was obtained strong magnets developed in two stages via solid-state reaction route under reducing atmospheres. With changing Er and Yb concentration, the green emission intensity increases with respect to the red intensity. The properties of two kinds of phosphors were compared with NaF and Na2Sif6 as reagents, respectively. It was found that luminescent properties of the samples prepared with NaF were http://www.chinamagnets.biz/ better. The result showed that heating temperature and holding time have significant influence on the properties of the phosphor, and the best green upconversion samples were obtained with heating temperature at 575℃for 8h. However, as heating temperature increase to 650℃, cubic NaYF4 was observed with diffraction and the green emission intensity were decreased due to the occurrence of the cubic NaYF4.
　　In order to improve the luminescent properties of NaYF4: Er3+/Yb3+ further, the orthogonal design of L9(34) was applied. In the experiments, four factors of the Er3+ concentration, Yb3+ concentration, heating time and holding time were considered, and the result showed that NaYF4 phosphor doped with 1mol%Er3+ and 20mol%Yb3+, and heated at 600℃for 6h, had the optimal green emission.Tm3+/Yb3+ co-doped NaYF4 phosphor with upconversion blue strong magnets emitting was synthesized via the solid-state reaction. With changing Tm and Yb concentration, the blue emission intensity increases with respect to the red intensity. Comparing the upconversion properties between hexagonal NaYbF4:Tm3+ and NaYF4:Tm3+/Yb3+, the optimal doping level was 0.2mol% of Tm3+ doping NaYF4 as well as 0.4mol% of Tm3+ doping NaYbF4; and the blue emission of NaYF4:Tm0.0023+,Yb0.43+ was higher and purer than that of NaYbF4:Tm0.0043+.As the emission of red transition was better in the samples with existence of oxides, YOCl:Yb,Er and YOF:Yb,Er phosphors were studied with the solid-state reaction method. In the YOCl:Yb,Er system, strongest red emission was obtained doped with 2mol% Er3+ and 20mol% Yb3+. Due to unstable upconversion properties of Y0C1 phosphors, Er3+/Yb3+ co-doped YF3-YOF phosphors were chosen. YF3:Yb3+/Er3+ behavied the lowest emission strong magnets intensity and the smallest ratio of red to green intensity. When the content of YOF phase was larger, the red emission intensity increased with respect to the green intensity and, the pure YOF phosphor co-doped with Er3+/Yb3+ showed the highest red emission.