Study On The Structure And Defect Structure Of New Type Of Germanium Salt Phosphor

At present, the main commercial white light emitting diodes (LEDs) phosphors, such as silicate and sulfide, contain many drawbacks. The extremely high synthesis temperature of silicate, the unstable chemical composition of sulfides phosphors, the expensive cost and low photoluminescence (PL) efficiency, all of which hinder their application. In order to solve above problems, we chose germanium material as host matrix, because of their low synthesis temperature and high stability. In addition, in the preparation processes, the defects would obviously influence the luminescence properties, so it’s essential to study the defects’structure to improve the luminescence efficiency. Although plenty of persistent materials have been developed, the details of the nature and mechanisms of the defects are still a subject of exploration, and the transport process of the charge carriers between trapping and emission centers remains unclear. Therefore, designing a facile approach to develop novel long persistent luminescence (LPL) phosphor with excellent intensity and lifetime for extending the family of LPL materials and exploring the nature of LPL process are essentially important and interesting. We found that germinates showed obviously self-activated phenomenon, in both PL and LPL processes, because the intrinsic defects not only act as the trapping centers in persistent process, but also as the exciton energy-level involved in the emission process. The emission of self-activated host is primarily rooted from the intrinsic defects. Therefore, investigations on the detailed defects structure can not only help us to improve the properties of PL, but also can help us simplify the model of LPL and the interaction between the intrinsic defects and the LPL emission. In summary, the results are of importance both for understanding the mechanism of persistence property, and designing and developing the LPL phosphors with excellent performance.In this paper, we mainly investigated the PL, LPL properties and defect states of germanates phosphors. The main points are as following:the self-excited germanate are prepared and in those materials, the detailed mechanism of PL, LPL, and the interaction between the intrinsic defects and the self-activated emission are discussed. Accordingly, the detail mechanisms of the LPL and PL process were discussed briefly.1. Germanates SrGeO3, Ca2Ge7O16 were prepared. Those phosphors were prepared through the solid state reaction.The PL of Eu3+ doped SrGeO3,Ca2Ge7O16 red light emitting phosphor were studied. The luminescent intensity can be improved both by co-doping with the charge compensators, and through the energy transfer from Sm3+-Eu3+. In addition, distinctive LPL phenomenon was observed in Ca2Ge7O16: Sm3+, which would lead to the tailing of luminescence process. After Eu3+ was doped, this phenomenon disappeared. What’s more, the defect structure of Ca2Ge7O16:Sm3+, Eu3+ was investigated.2. The self-activated properties of Ca2Ge7O16 and Na2ZnGeO4 were investigated. In Ca2Ge7O16, the unique emission of Ca2Ge7O16 related to the creation of the oxygen vacancies was proved. The results indicate that there are two different types of traps, which are attributed to oxygen and calcium vacancies, respectively. Both of them not only act as the trapping centers, but also as the exciton energy-level involved in the emission process. Besides, the LPL energy transfer process from Ca2Ge7O16 host to Sm3+ was confirmed. The color of the LPL luminescence could be adjusted from blue to red with increasing concentration of Sm3+ accordingly. In addition, we explored the defects properties of self-activated phosphors Na2ZnGeO4 host. The result indicates that the self-activated phenomenon results from the intrinsic defect of Zn vacancies. Zn vacancies act not only as an exciton energy-level participated in the PL process, but also as trapping centers contributing to the LPL process. Furthermore, the energy transfer processes from Na2ZnGeO4 host to Tb3+/Mn2+ ions in PL and LPL were identified. Accordingly, the LPL colors changed from blue to green. Notably, a new approach of tunable LPL method can be realized via LPL energy transfer from host-sensitizer to emitting centers with the assistance of traps, which could help us verifying the mechanism of LPL and reducing the cost.3. Because low-dimensional chain crystal structure and ring structure are beneficial to the formation of the trap level and excited state level. It especially could provide an effective transmission path in one direction between luminescent and trapping centers. In this chapter, the low-dimensional structure of the SrGa2O4 host with self-activated phenomenon was studied. In this work, the energy transfer processes from the SrGa2O4 host to Bi3+ ions in the PL and LPL process were identified. The results illustrate that SrGa2O4:Bi3+ exhibited excellent luminescence properties, including PL, LPL, and photostimulation. The results indicated that SrGa2O4:Bi3+ could be a new member of the yellow phosphors, which also provide potential applications in the fabrication of LED, persistent phosphors and optical memory.