Research Of Oxynitride Phosphors For Novel Lighting And Display Devices

The lighting technology is one of the most basic demands in daily life and therefore has been growing rapidly with the development of the society. In particular, the new lighting technologies, such as LEDs (light emitting diodes) and PDP (plasma flat-panel display technology), etc., have made rapid progress in recent years. Compared to traditional technologies, the LED and the PDP technologies have the following advantages:high energy conversion efficiency and environmental friendliness without (low) pollution, high image quality, stable performance in all-digital mode, and therefore has been admitted both in academic and market.In lighting and display equipments, phosphors which convert the light from the light source into different colors are indispensable components. Moreover, the phosphors directly determine the quality of the observers’final experience. As phosphors have such an important position, they have gotten more and more attention along with the rapid development of the lighting technology. The conventional phosphors are mainly oxides, sulfides, oxysalts and so on. However, only a very limited number of present phosphors can meet the minimum requirements for the new generation of lighting and display technology. Therefore, to modify existing and explore new phosphor materials is extremely urgent.A new class of inorganic phosphors, namely rare-earth-doped silicon oxynitrides, has attracted much attention in recent years due to their high chemical and thermal stability as well as their unusual luminescence properties. In order to research the oxynitrides, the present work studied the rare-earth ions activated CaSi2O2N2on the synthesis conditions, luminescent properties, optical optimization, and the energy level distribution. On the other hand, the influence of Si-N codoping in the aluminate phosphors has also been studied.In Chapter Ⅰ, the development process of lighting and display technologies was briefly introduced, and a brief description about conventional and newly phosphors was given with relevant literatures and technologies.In Chapter Ⅱ the experimental process of this work is described, including the starting materials, synthesis equipment, the synthesis process, material testing techniques.Chapter Ⅲ consists of three parts.(1) The synthesis conditions, crystal structure, and the photoluminescence properties of Eu2+doped CaSi2O2N2were studied. The results show that in the VUV region, the excitation corresponds to the host absorption, and the energy transfer from host to activators exists. The excitation from ultraviolet to blue originates from the electronic transitions from the4f ground level to the5d levels of Eu2+. The light emission located in the green-yellow region and corresponds to the electronic transitions from the5d levels to the4f levels.(2) The photoluminescence properties of CaSi2O2N2:Eu2+may be greatly impact by Lanthanide3+ions. The optimization mechanism was studied in detail by the case of La3+doping. The La3+ions could stabilize Ca2+vacancies, inhibit the oxidization of Eu2+to Eu3+, and consequently increase the total number of activators. Meanwhile, new defect-energy levels were detected. These defects might capture electrons which were excited from Eu2+to the conductive band, and then detrap a considerable amount of the electrons back to the5d levels of Eu2+ions.(3) The influence of some other co-dopants was also discussed in the material.In Chapter IV, The photoluminescence properties of different lanthanide ions in the material were characterized and analyzed systematically. Energy transitions attributed to electron transfers from4f to4f (ff), from4f to5d (fd), from5d to4f (df) and charge transfer (CT) transition were obtained and classified. Finally, an energy-level diagram of lanthanide-ions in CaSi2O2N2was proposed. The diagram matches perfectly with the experimental results and explains the luminescence properties of lanthanide-doped CaSi2O2N2phosphors.In Chapter V, the impact on the photoluminescence and afterglow properties of CaAl2O4:Eu2+via Si-N co-doping was discussed. A small amount of Si-N was introduced into the conventional phosphor CaAl2O4:Eu2+, and obviously improved the photoluminescence intensity. It was proved that the Si-N bands preferred to replace the the Al-O near Eu2+though electron paramagnetic resonance (EPR) measurements. Since Si-N bond has a shorter bond length, they may improve the lattice rigidity around Eu2+. As a result, the energy loss caused by the lattice vibration may be reduced.In Chapter VII, Tb3+and/or Ce3+activated CaSiO3and Ca2SiO4phosphors were synthesized and their photoluminescence properties were discussed.Chapter VII consists of summary and future work outlook.