Synthesis And Characterization Of Magnesium Aluminum Isopropoxide And Aluminate-based Phosphors

As good candidates for full color emitters, aluminate-based phosphors have drawn extensive attention, especially for their application in plasma display panels. Magnesium aluminum isopropoxide is widely employed in the preparation of aluminate-based advanced materials. Among the physical and chemical properties, purity of raw materials plays a vital role. It is necessary to guarantee quality by controlling the content of contaminants. Trace of iron impurity could cause severe quenching of luminescence. Thus, it is necessary to remove iron from magnesium aluminum isopropoxide. In addition, the products derived from traditional synthetical methods usually suffer from several problems. The main points lie in its unstability that caused either by impurity in raw material or heat-resistance and aggregation that is brought by traditional solid-state reaction. Therefore it is urgent to find new synthetic methods and alternative luminescent materials with appropriate raw material that is accessible and high purity. In the present work, we focus our attention on the synthesis and purification of magnesium aluminum isopropoxide, development in synthetic method of aluminate-based phosphor and improvement in luminescent properties and morphological control of the aluminate phosphor. The results are given as follows:1. Different synthetic procedures have been considered. A one-pot two-step reaction route was chosen to synthesize alkoxide with different ratio of Mg/Al. A facile and effective method has been employed to remove the trace iron impurity in magnesium aluminum isopropoxide. Effective prevention of iron from its reaction with isopropanol or isopropoxide is generated by adding NP. Thus the iron content can be reduced from more than 20 ppm to less than 5 ppm in the resulting products.2. Different wet chemical methods are applied to improve the performance of aluminate-based phosphors. Barium or strontium magnesium aluminate obtained from a nano-coating route showed higher intensity compared with those from traditional solid-state reaction. The precursor had core-shell structure so that the reaction of the materials could be confined in the given field. Therefore hexagonal plate-like crystallization can be inhabited, resulting in quasi-spherical fine products. As for the SAM sample prepared by hydrocarbonate-gel method, photoluminescence intensity could be enhanced by co-doping of Zn and B. XRD patterns revealed that the sample that had the highest intensity also displayed the best crystallinity. The reason may lie in the improvement of host cell parameters by bigger Zn2+cation with the combination of flux.3. MgAl2O4:Ln (Ln=Eu3+, Tb3+) hollow microspheres have been obtained through hydro-thermal treatment and further calcination process. The resulting products have good dispersity with diameter in the range of 1～2.5μm. On changing the Mg/Al ratio, particle size and thickness of the shell were controlled to some extent. Energy transfer was observed from Tb3+ to Eu3+by simply regulating the molar ratio of Eu/Tb. Inorganic and organic luminescent complex could also be obtained by introducing Alq3 in the mesoporous MgAl2O4:Eu3+ and tunable emission from green to red can also be achieved by changing the ratio of the two components.4. Magnesium aluminum hydroxide complex with different morphologies have been synthesized. Uniform 3D rosette-like Tb3+-doped LDH/AlOOH heterophasic architectures assembled from nanosheets building blocks were successfully prepared via ethylenediamine-assisted hydrothermal method for the first time. It was found that ethylenediamine was crucial to the rosette-like architectures, in which each microflower was assembled by layer-by-layer growth of homocentric superposed nanosheets. It could also be concluded that high reaction temperature was in favor of assembly of the nanosheets building units. Photoluminescence measurements indicated that products possess multiple and tunable emissions in the blue region under different ultraviolet light excitation.