Synthesis And Fluorescence Properties Of Mn⁴⁺ Doped Materials

With the gradual expansion of the light emitting diode（LED）market,,the immature technology of red phosphor has become a key factor limiting the development of LED.Therefore,exploring highly efficient and stable red phosphors has become a hot research topic nowadays.Following the rise of the commercial Eu²⁺-doped nitride phosphors,Mn⁴⁺-doped fluoride red phosphor has aroused lots of attention and exploration owing to the unique fluorescent characteristics.Mn⁴⁺ions are located at the center of the octahedral structure in the fluoride matrix,which can split the ground state energy level ⁴A1 and the lowest excited state energy level ²Eg by the strong octahedral field,and affect the fluorescence properties of phosphor.Moreover,the ⁴A2g→⁴T1g UV absorption transition caused by the 3d³ electron configuration of manganese ion and the ⁴A2g→⁴T2g transition excited by blue light are both spin-allowed transitions.The emission of red and far-red light can be achieved by the energy level transition of Mn⁴⁺.The luminescence properties enables Mn⁴⁺-doped fluoride phosphors to be applied in the LED assembly.In this thesis,fluoride matrix Cs2Ti F6 was synthesized by hot injection and ion exchange methods without the usage of hydrofluoric acid,followed by the Mn⁴⁺doping to synthesize Cs₂Ti F₆:Mn⁴⁺red phosphor,while A₂Ti F₆:Mn⁴⁺（A=Na,K）and Li₃Al F₆:Mn⁴⁺phosphors were successfully prepared by facile approaches including hydrothermal and co-precipitation methods.The structure and elemental composition of the synthesized phosphors were analyzed by X-ray diffraction,energy dispersive characterizations such as X-ray spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscopy,and etc.Besides,the fluorescence properties of the prepared phosphors were also investigated.Results show that the excitation and emission ranges of the prepared phosphors are compatible with the other components of LED devices.Subsequently,the doping ratio was optimized,and the resulted phosphor with the optimal luminescent properties are used to assemble LED devices for further test.Results show that the prepared phosphors can effectively tune the color temperature and color rendering index of LEDs,and have a large developing potential in the field of red phosphors for LED application.