Synthesis And Application For WLED Of Transition Metal Mn⁴⁺ Doped Oxide Red Phosphors

Phosphor converted light emitting diodes（pc-LEDs）are known as green light sources,which overcome a series of disadvantages such as short lifespan,large size,unfriendly environment and so on.However,it was greatly restricted for application due to the commercial white light emitting diodes（WLED）obtained by the blue chip excited the yellow phosphor with low color rendering index and high color temperature.Therefore,researchers found that doping red phosphors can improve light efficiency and color rendering to broaden their application.Compared with rare earth ion doped red phosphors,Mn⁴⁺doped oxide red phosphors have become a hot spot in the research of WLED and plant lighting LEDs due to their advantages such as easy availability of raw materials,low prices and simple preparation conditions.Therefore,this thesis focuses on the synthesis of new Mn⁴⁺doped oxide red phosphors and explore the application for LEDs.The main research contents are as follows:The Ba₂LuNbO₆:Mn⁴⁺red phosphors with double perovskite structure were successfully synthesized by high temperature solid phase method in air atmosphere.The crystal structure,morphology,composition and optical properties of Ba₂LuNbO₆:Mn⁴⁺phosphors were systematically studied by X-ray diffraction,Rietveld refinement,SEM,EDS and photoluminescence spectra.Under excitation with 380 nm near-ultraviolet light,the phosphor emits bright red light around 670 nm.Mn⁴⁺-activated Ba₂LuNbO₆ phosphors have high thermal stability,the fluorescence intensity maintains about half of the initial intensity at 400 K.LED devices were fabricated using 365 nm near-ultraviolet chips with commercial blue,green phosphors and Ba₂LuNbO₆:Mn⁴⁺red phosphors,which have good color rendering（CRI=84.4）and good color stability,the results indicate that Ba₂LuNbO₆:Mn⁴⁺red phosphor have great potential in the field of WLED and plant growth light.A series of Ba₂LaTaO₆:Mn⁴⁺red phosphors were prepared by sol-gel method.The structure,morphology,optical properties,energy band structure and thermal stability of Ba₂LaTaO₆:x Mn⁴⁺phosphors were systematically studied.Under the excitation of 365 nm near-ultraviolet light,the sample emits bright red light in the range of 600-740 nm with the highest peak at 682 nm.The mechanism of concentration quenching was discussed and the influence of crystal field strength and electron cloud effect were analyzed.In addition,Ba₂LaTaO₆:Mn⁴⁺red phosphor was used to pack into the LED,which have potential to be applied in WLED and plant lighting.The La₂Li TaO₆:Mn⁴⁺red phosphors doped with different charge compensators(Zn²⁺,Mg²⁺,Ca²⁺,K⁺,Na⁺)were successfully synthesized by high temperature solid phase method.The influence of different charge compensators on its luminescence properties was investigated.After doping different compensator ions,the luminescence intensities of the samples are enhanced.Under excitation of 315 nm ultraviolet light,the sample emits red light of 711 nm.When doped with Zn²⁺,the luminescence intensity increases to the maximum.La₂Li TaO₆:0.3%Mn⁴⁺,1%Zn²⁺have good thermal stability,the luminescence intensity reaches 91.5%of the initial luminescence intensity at 423 K.The optimized La₂Li TaO₆:0.3%Mn⁴⁺,1%Zn²⁺was used to prepare the full-spectrum WLED,which has higher color index（84.5）and lower color temperature（3928 K）,the emission spectrum and the absorption spectrum of the phytochrome P_FRhave obvious overlap,the results indicate that the phosphor can be applied in full-spectrum WLED and plant lighting.