Preparation And Luminescent Properties Of Aluminum Based Phosphors For White Light Emitting Diodes

Compared with the traditional light source, LED has the advantages of energy saving, high efficiency, small volume, long lifetime, quick response, low driven voltage, anti-vibration and so on. Thus, LED is regarded as the fourth generation green illuminant source. Until now, commercialized phosphors are usually prepared by a conventional solid-state reaction method. This method has a few inherent disadvantages in requiring high calcination temperature and long processing time, which lead to the formation of coarse agglomerated particles. To obtain particles in the size of several microns, extensive ball milling is used to grind the coarse agglomerated particles generally. This process often contaminates the phosphors and decreases their luminescent intensity greatly.In this thesis, two different routes were adopted to get rid of coarse agglomeration of products and high energy consumption induced by the conventional solid-state reaction method respectively.On the one hand, an epoxide-driven rapid sol-gel method was used to synthesize amorphous Al2O3 microspheres as a precursor, and the precursor turned to AlN microspheres after the nitridation reaction in NH3 atmosphere. The as-synthesized monodisperse AlN microspheres show high degree of crystallinity, regular spherical morphology, controllable particle size and narrow particle size distribution. On this basis, UV light excited phosphors including AlN:Mn2+ red light emitting microspheres (excited at 280 run, emitting at 605 nm), SrAl2O4:Eu2+ green light emitting cage-like microspheres (excited at 365 nm, emitting at 520 nm)?CaAl2O4:Eu2+ blue light emitting microspheres (excited at 330 nm, emitting at 440 nm) and Sr2MgAl2O36:Mn4+ red light emitting microspheres (excited at 326 nm, emitting at 651 nm) were successfully prepared and exhibited brilliant luminescent properties. XRD?SEM?TEM?FTIR?PL and other kinds of characterizations were implemented to analyze the microstructure and luminescent properties of both the precursors and the final products. The research focused on the mechanisms of AlN microsphere formation, SrAl2O4:Eu2+ cage-like microsphere formation, luminescence enhancement by cage-like structure microsphere and the influence of Ca2+ concentration on CaxSr1-xAl2O4:Eu2+ luminescence properties. Furthermore, the influences of heat treatment, activator doping contents and other experimental formulations on the luminescent performance of the products were also studied.On the other hand, a precipitation method was adopted to synthesize urea coordination complex of Al3+ cation, and the precursor turned to AlN nanocrystals after the nitridation reaction at merely 800 ? in NH3 atmosphere, a much lower temperature than conventional solid-state method. On this basis, Ca2AlSi3O2Ns:Eu2+ green light emitting phosphor (excited at 303 nm, emitting at 500 nm), Ca2AlSi3O2Ns:Mn2+ red light emitting phosphor (excited at 280 nm, emitting at 630 nm) and Ca2AlSi3O2N5:Sm3+ red light emitting phosphor (excited at 303 nm, emitting at 650 nm) were successfully prepared at the temperature as low as 1000?. XRD?SEM?TEM? PL and other kinds of characterizations were also carried out to analyze the microstructure and luminescent properties of both the precursors and the final products. The research focused on the mechanisms of nanocrystals formation at a rather low temperature. Furthermore, the influences of heat treatment and activator-doping concentration on the luminescent performance of the products were also studied.