Preparation Technology,Structure And Properties Of Rare Earth-Doped YF₃ Fluorescent Powders And Perovskite Titanates Multifunctional Ceramics

Inorganic fluoride-containing hosts exhibit low vibration energy, high iconicity and small extension effect of electron clouds effect, and thus have a potential application in biomedical imaging, anti-fake and illumination. Among inorganic fluoride-containing materials, YF₃:Eu³⁺ is an important earth-doped inorganic fluoride-containing material; however, it is still an interesting topic to improve the fluorescence efficiency of YF₃:Eu³⁺. On the other hand, there is an increasing demand in the miniaturization and multifunction of electronic/microelectronic devices. Therefore, the materials with the coexistence of two or above characteristics have attracted considerable attention. Among multifunctional materials, rare earth-doped perovskite titanates with excellent ferroelectric / piezoelectric and fluorescent properties have been extensively studied. This thesis includes two parts research content:（1） modulating the microtopography of the rare earth doped YF₃ fluorescent powder and studing the flurescent property of the material;（2） the preparation technology, piezoelectricity, ferroelectricity and fluorescence of rare earth doped Ba TiO₃- and Bi_0.5Na_0.5TiO₃- multifunctional ceramics. The main research contents and results are listed as follows:（1） YF₃:x Eu³⁺, y%Bi³⁺（x = 0-0.2, y = 0-1.5） material were successfully synthesized and the phase structure, micro-morphology of grains and the fluorescence of the materials were systematically studied by optimizing hydrothermal route, the concentration of Eu³⁺and Bi³⁺, the volume of HNO₃, holding time, reaction temperature and source of fluoride. The concentration of Eu³⁺and Bi³⁺ ions have an obvious effect on the phase structure, micro-morphology of crystal particle and fluorescence. Especially, the doping of Bi³⁺ exhibits a remarkable improvement in the fluorescence of materials. The optimum composition of the materials are x=0.125 and y=0.5%.The regular octahedral grain with trun-cated edges and corners has been obtained at VHNO₃=11ml. The microstructure and micro-morphology of the material have an obvious variation with the reaction temperature increasing and the optimum reaction temperature is 200 oC. As holding time increases, the microstructure and micro-morphology of material have been changed obviously and the optimum hold time is 18 h. Moreover, BaF₂, CaF₂, MgF₂, LiF, NaF, KF, NH₄F and NH₄HF₂ were used as different source of fluoride, respectively. The influence of cations with different ionic radius and electrical charge on the structure and property of the material have been discussed.（2）Ba_0.85Ca_0.15Ti_0.9Zr_0.1O_3-x mol% Dy³⁺（x=0-4.0） ceramic samples were fabricated by the traditional solid state reaction method. The microstructure, micro-morphology and properties of the ceramic with increasing x have been discussed and the results exhibit that all of the samples are pure tetragonal phase perovskite structure. As x=0.5, the sample possess a relatively high piezoelectricity; as x=0-2.0, the sample possess a relatively high ferroelectricity; as x=2.0, the optimal fluorescence of the material has been obtained. And thus when the doping concentration is x=0.5-2.0, the ceramic prepared in the work possess simultaneously excellent piezoelectricity, ferroelectricity and fluorenscent property.（3）0.94(Bi_1-xEr_xNa)_0.5TiO₃–0.06 Ba TiO₃（x=0-0.036） samples were successfully fabricated by a traditional solid state synthesized method. The influence of dwell time ts, sintering temperature Ts, the poling electric field and concentration of Er³⁺ on the microstructure, micro-morphology and properties of the ceramic have been discussed in in detail. The experimental results confirmed that the samples are coexistence phase structure of hexagonal and tetragonal phase. And partial substitution of Er³⁺ for Bi³⁺ can effectively improve the piezoelectricity and ferroelectricity in the ceramic. The sample with x=0.012 exhibits a good ferroelectricity（29.6 μC/cm2） and piezoelectricity（181 p C/N）, while as x=0.032, the sample of ceramic possesses optimal fluorenscent property. When Ts=1200 oC and ts=2 h, the ceramic displayes excellent piezoelectricity; at Ts=1140-1160 oC and ts=2 h, the sample possesses an excellent up-conversion and down-conversion fluorenscent property. The fluorenscence of ceramic which was polarized in the range of the poling electric field of 2.5–3.5 k V/mm has been increased tremendously.