Synthesis And Luminescence Performance Optimization Of Mn⁴⁺ Doped Fluoride Red Phosphor For White LED

As the fourth generation light source,white light emitting dilde（LED）has the advantages of low energy consumption,high energy conversion efficiency,long life and environmental friendliness,which has attracted extensive attention of researchers.The commercial white LED composed of In Ga N blue chip and YAG:Ce³⁺yellow phosphor is applied in many fields.However,the lack of red light limits its application in the field of backlight display and indoor lighting.Compared with rare earth doped red phosphor,Mn⁴⁺activated fluoride red phosphor has the characteristics of rich raw materials,broadband excitation and narrowband emission.This shows that Mn⁴⁺activated fluoride red phosphor matches the emission peak of In Ga N blue chip,and can be used as a candidate material for warm white LED.Therefore,a variety of red phosphors,including（NH₄）₂Na MF₆:Mn⁴⁺（M=Al,Ga and In）,Na₃Li₃In₂F₁₂:Mn⁴⁺,K₂Si F₆:Mn⁴⁺,Li⁺and K₂Si F₆:Mn⁴⁺,Li⁺@Ba SO₄,were synthesized by coprecipitation,hydrothermal and solvothermal methods,the luminous characteristics were discussed,and the warm white LED were formed by combining the prepared red phosphors,In Ga N blue chip and YAG:Ce³⁺yellow phosphor.The main research contents of this thesis are as follows:（NH₄）₂Na Al F₆:Mn⁴⁺（NNAFM）,（NH₄）₂Na Ga F₆:Mn⁴⁺（NNGFM）and（NH₄）₂Na In F₆:Mn⁴⁺（NNIFM）red phosphors were synthesized by hydrothermal method and characterized by powder X-ray diffractometer,field emission scanning electron microscope and energy dispersive spectrometer.Under 470 nm blue light,the strongest emission peaks of（NH₄）₂Na MF₆:Mn⁴⁺red phosphor are 637 nm（NNAFM）,636 nm（NNGFM）and 634 nm（NNIFM）.This blue shift phenomenon was analyzed by crystal field strength and nephelauxetic effect.In addition,the optimal doping concentrations of NNAFM,NNGFM and NNIFM red phosphors are 2%,2%and 4%,respectively.The concentration quenching mechanism is attributed to dipole-dipole（d-d）interaction.At 150℃,NNGFM red phosphor still maintained 31%of the initial luminous intensity.Finally,three kinds of red phosphors were combined with In Ga N blue chip and yellow phosphor(YAG:Ce³⁺)to form warm white LED devices.LED device(blue chip-YAG:Ce³⁺-NNGFM)has high color rendering index（Ra=90.1）and low correlation color temperature（3422 K）.A new dodecafluoride red phosphor Na₃Li₃In₂F₁₂:Mn⁴⁺with good waterproof property was obtained by solvothermal method.The crystal structure,optical properties,micro-morphology,element composition,thermal stability and water resistance of Na₃Li₃In₂F₁₂:Mn⁴⁺phosphor were analyzed.Under 468 nm blue light excitation,Na₃Li₃In₂F₁₂:Mn⁴⁺phosphor has narrow band red light emission（590-650 nm）.The optimal doping concentration of Na₃Li₃In₂F₁₂:Mn⁴⁺red phosphor is 3%,and the concentration quenching mechanism is dipole-dipole（d-d）interaction.When the temperature rises from room temperature to 150℃,the luminous intensity of Na₃Li₃In₂F₁₂:Mn⁴⁺phosphor maintains28%of the luminous intensity at room temperature.In addition,compared with commercial K₂Si F₆:Mn⁴⁺red phosphor,Na₃Li₃In₂F₁₂:Mn⁴⁺has better waterproof stability.Finally,the In Ga N blue chip,yellow phosphor(YAG:Ce³⁺)and Na₃Li₃In₂F₁₂:Mn⁴⁺red phosphor are used to form a warm white LED with CRI of 87 and CCT of 3386 K.The optical properties and water resistance of K₂Si F₆:Mn⁴⁺red phosphor was optimized by doping Li⁺and coating Ba SO₄.The K₂Si F₆:Mn⁴⁺,Li⁺red phosphors were synthesized with Li F as lithium source.The luminous intensity of K₂Si F₆:Mn⁴⁺,Li⁺phosphor is 1.3 times that of K₂Si F₆:Mn⁴⁺phosphor.In order to improve the waterproof property of K₂Si F₆:Mn⁴⁺phosphor,Ba SO₄ layer was coated on the surface of K₂Si F₆:Mn⁴⁺,Li⁺samples.The coating layer enables K₂Si F₆:Mn⁴⁺,Li⁺@Ba SO₄ red phosphors to maintain 80%of the initial luminous intensity after soaking in water for 6 h.In addition,the three phosphors have higher luminous intensity at 150℃.Finally,three kinds of red phosphors are combined with In Ga N blue chip and yellow phosphor(YAG:Ce³⁺)to form warm white LED devices.The warm white LED device based on K₂Si F₆:Mn⁴⁺,Li⁺@Ba SO₄ red phosphor has excellent performance（CCT=3558 K,CRI=91.4）.