Study On The Thermal Stability Mechanism Of Fluorescent Materials For LEDs With The Aid Of Defect States

Thermal stability has become a bottleneck restricting the further development of fluorescent conversion white light emitting diodes?LED?.Trap theory and structural rigidity of materials are the factors affecting thermal stability summarized by most researchers,which is helpful for the design of white LED phosphors with high thermal stability.For the trap theory,the detailed movement process of the internal carriers and the thermal stability mechanism under the trap theory are still unclear.Based on the abundant defect structure in electron capture materials,the detailed movement process of carrier release in traps at high temperature is discussed,which provides theoretical guidance for the design of new phosphors with high efficiency.In this paper,several Sr₂Ga₂GeO₇:Pr³⁺,CaAl₂O₄:Eu²⁺,Tm³⁺,Sr₃SiO₅:Eu²⁺,Tm³⁺fluorescent materials with abundant defect structures were synthesized by high temperature solid-state method.The unequal substitution of rare earth doping is used to adjust the defect structure,especially to increase the depth and concentration of the defect.Based on the process of trap capture and release in materials and the energy level structure of some rare earth ions,the process of carrier release in materials at high temperature was studied in detail.In Sr₂Ga₂GeO₇:Pr³⁺materials,there is no trapt state in the low-energy illumination,and the multi-phonon relaxation process and the non-radiation relaxation process work together to ensure the high thermal stability of the two different levels of luminescence.High-energy light irradiation,the interaction of intervalent charge transfer states?IVCT?and defects leads to the quenching of green light emission and zero-thermal quenching of red light emission.By reconstructing the defect states of CaAl₂O₄:Eu²⁺,Tm³⁺,the dynamic processes of traps filling,thermal quenching and traps release were studied.Thereby,the thermal quenching mechanism of the material with deep defect release inhibition at high temperature is simplified and finally determined.A yellow electron capture material Sr₃SiO₅:Eu²⁺,Tm³⁺,which can be used in practical applications,was designed by using the thermal stability mechanism that we studied.Zero thermal quenching phenomenon of the material was realized at 393K.The high efficiency filling process of deep defects at high temperature plays an important role in the zero thermal quenching of materials,and this traps structure can ensure that the luminescence of materials is in a long-term stable state.Using Sr₃SiO₅:Eu²⁺,Tm³⁺fluorescent materials that we designed,white LED devices with excellent performance were fabricated,which provided ideas for the design of new and excellent multi-color fluorescent materials.