Theoretical And Experimental Research On Modification System Of YAG:Ce³⁺ Phosphor And Exploration Of New Materials System

White LED with advantages of low energy consumption, long lifetime and environmentally friendly, has been widely used in lighting and display fields. White LED fabricated by traditional YAG:Ce3+ yellow phosphor with blue LED chip is facing with problems of high color temperature, low color rendering index and hard to meet the demand of high energy density excitation, which become barriers limiting its applications. This thesis focuses on the problems, performed theoretical and experimental research on modification system of YAG:Ce3+ phosphor and some explorations of new materials system within garnet structure.DFT calculation is performed on geometry optimization to study the behavior of doped lanthanide ion in YAG:Ce3+ modification system. And the ions in dodecahedral sites show a phenomenon of ion arrangement in accordance with the ionic radius successively under the lattice stress caused by structural rigidity. This special and rare behavior can influence the luminescence by affecting the local structure of Ce3+ ions, becoming a structural controlling factor of garnet phosphor. Based on this optimized structure, the effects of the cation doping on electronic structure were studied with HSE06 method, and the approximate relations between spectrum property and thermal quenching property with electronic structure were tried to establish, and some relatively accurate simulated values of the spectrum property and thermal quenching property of YAG:Ce3+ modification system were successfully obtained.The theoretical calculated blue-shift of emission spectrum and enhanced thermal quenching property of La3+ co-doped YAG:Ce3+ was verified in experimental. In addition, luminescence enhancement with appropriate amount of La3+ addition is also observed. The promoted luminescent properties are ascribed to the tight and highly ordered structural arrangement of La3+-Ce3+-Y3+, which effectively prevents the Ce3+ ions gathering and the interactions between phonon and lattice. Basing on this effect, La3+ was considered to be introduced into Y3(Al,Si)5(O,N)12:Ce3+ system, and as expected, blue shift of spectrum and enhancement of luminescence and thermal quenching property was also observed. However, the coordination of Ce3+-N3" was gradually changed to La3+-N3- due to selective coordination of N3" with larger ion in dodecahedral site, leading to spectrum changed a lot both in shapes and peaks.Moreover, a phase formation rule of garnet compounds is analyzed according to structural characteristics of garnet, and two series of Ca2LaZr2Ga3O12:Ce3+ and Ca3Zr2SiGa2O12:Ce3+ was designed and synthesized. The crystal structure and photoluminescence properties and related mechanism were studied, thermal ionization rather than cross relaxation is revealed to be the dominant mechanism of thermal quenching property in these phosphors through calculation, and site differentiation of Ca3Zr2SiGa2O12:Ce3+ is proposed through structural and fluorescence decay analysis.