The Synthesis And Properties Of Silicon-oxynitride Phosphors

With the increasing serious energy crisis, there has been a growing focus on the research in energy saving and environment protection. White light-emitting diodes (white-LEDs) show an outstanding potential in general illumination applications due to their high luminous efficiency, low energy consumption, low working voltage, short response time, long life time and small volume, leading to a huge market value. It is believed that LED-based solid state lighting is the next generation lighting source for common illumination. However, a single chip can not generate white light because it is impossible to cover the full wavelength range of the visible light. Nowdays, commercial white LED normally uses a monochromatic chip covered by light conversion phosphors.As an essential part, phoshphors strongly affect the quality of LEDs, such as luminous efficiency, color temperature, color rendering index and life time. Recently, numerous studies show that many silicon oxynitrides doped with rare earth are the most promising phosphors for white LEDs, because of their high co valence, tunable wavelength, available for ultraviolet or blue light excitation, long wavelength emission and low temperature quenching.However, the conventional solid-state reaction approach for synthesizing (oxo)nitridosilicate phosphors using high-purity nitrides leads to difficulties in powder mixing, high costs, and low yields in industrial application. From this viewpoint, a simple, cost-effective, facile and potential morphology-controlling direct silicon nitridation method was developed in this paper. Some outstanding phosphors with different nitrogen contents, such as SrSi2N2O2:Eu2+, Sr2Si5N8:Eu2+, Ba2Si04:Eu2+, BaSi2O2N2:Eu2+, BaSi6N8O:Eu2+and Ca-a-sialon:Eu2+, were pareparedied by solid state reaction, gas reduction nitridation and direct silicon nitridation routes. Relative experimental conditions were studied and their possible mechiniasms have also been investigated, the advantages of the novel synthesis process have been pointed out.This paper is divided into six chapters.Chapter1mainly introduces the principle of LED, the structure of white light LEDs, silicon oxynitride phosphors and their preparation method. At the end, the main purpose of this paper and the related theoretic basis are put forward. Chapter2is the experimental procedure, including the starting materials, synthesis equipments, characterization methods, et al.In chapter3, SrSi2N2O2:Eu2+and Sr2Si5N8:Eu2+phosphors have been prepared by the solid state reaction, gas reduction nitridation and direct silicon nitridation methods. Simultaneously, some synthesis conditions have been discussed, such as baking temperature, holding time, temperature increasing rate, reaction atmosphere, gas flow rate and milling time. At last, the possible mechanisms of the direct silicon nitration method have been proposed too.In chapter4, Ba2Si04:Eu2+, BaSi2O2N2:Eu2+and BaSi6N8O:Eu2+were synthesized by solid state sintering, gas reduction nitridation and direct silicon nitridation method. The reaction processes have been discussed at the end.In chapter5, another excellent oxynitride phosphor, Ca-α-sialon:Eu2+has been prepared by solid state sintering, gas reduction nitridation and direct silicon nitridation methods. The different products have been studied in details for further discussion.In chapter6, a short conclusion has been made and some development directions have been suggested.