Controllable Synthesis And Luminescent Properties Of Transition Metal Manganese Ion Activated Red Phosphors

White LEDs have the characteristics of energy saving,convenience,high efficiency,long lifetime and environmental protection compared with traditional artificial light sources such as incandescent lamps and fluorescent lamps.At present,the main strategy of packaging commercial white LED is to mix yellow phosphors Y3Al5O12:Ce³⁺with organic resin and In Ga N blue light chip.However,due to the lack of red component,the white LEDs have low color rendering index(CRI,Ra<80)and high correlated color temperature(CCT>5000 K),so they are not suitable for home lighting or background display.Mn⁴⁺-activated red phosphors can be used to improve the optical properties of white LEDs and realize warm white light emission.Owing to the unique 3d³ electronic configuration of Mn⁴⁺,the crystal field environment of the matrix material has a great influence on the photoluminescence properties of Mn⁴⁺.Therefore,it is of great significance to explore the influence of matrix materials with different physical and chemical properties on the luminescent properties of Mn⁴⁺.However,Mn⁴⁺-activated fluoride red phosphor has the problems of different refractive index for organic resin,poor water stability and single fluorescence color,which greatly limits the application of the phosphors in some specific lighting fields.This dissertation is focused on synthesizing Mn⁴⁺-doped red phosphors with different substrates and studying the luminescence characteristics of Mn⁴⁺in different substrates as well as the influence of reaction conditions on the structure,morphology and luminescence properties of the phosphors.In addition,the performances of Mn⁴⁺-doped fluoride red phosphors are improved by constructing one-dimensional luminescent nanofiber film and core-shell structure,thereby the application of phosphor is further expanded in warm white LED.The main research contents are as follows.1.Mn⁴⁺equivalent doping Ba GeF6 and K2GeF6 red phosphors were synthesized by hydrothermal and coprecipitation methods,respectively.The effects of different synthesis conditions on the crystal structure,morphology,and luminescent properties of Ba GeF₆:Mn⁴⁺and K₂GeF₆:Mn⁴⁺phosphors were studied in detail.The Ba GeF₆:Mn⁴⁺and K2GeF6:Mn⁴⁺red phosphors have two broad and strong absorption bands in the near ultraviolet and blue light regions.Under the excitation of blue light,they show strong red emission.The optimum doping concentration of Mn⁴⁺in Ba GeF6 and K2GeF6 matrix is 2%and 9%,respectively.Moreover,the dipole-dipole interaction was determined to be the main reason for concentration quenching.In addition,Ba GeF6:Mn⁴⁺and K2GeF6:Mn⁴⁺samples have good thermal stability.Using these two phosphors as red components,warm white LEDs with low color temperature(4766 K,3882 K),high color rendering index(Ra=86.3,90.4)and high lumen efficiency(67.57 lm/W,125.84 lm/W)were obtained,respectively.2.Mn⁴⁺non-equivalent doping Na3Al F6 with cryolite structure and(NH4)2Na In F6with elpasolite structure red phosphors were synthesized by coprecipitation and hydrothermal methods.Compared with the coprecipitation method,hydrothermal treatment can successfully optimize the morphology and luminescence intensity of the red phosphors.The crystal field strength(Dq),Racah parameters(B and C)and the nephelauxetic ratio?1of Na3Al F6:Mn⁴⁺sample were calculated.The luminescent properties and morphology changes of Na3Al F6:Mn⁴⁺phosphors were systematically studied by adjusting the reaction conditions.In addition,the temperature quenching mechanism of(NH4)2Na In F6:Mn⁴⁺red phosphor was also analyzed in detail.Using(NH₄)₂Na In F₆:Mn⁴⁺and Na₃Al F₆:Mn⁴⁺phosphors as red components,warm white LEDs with low color temperature(3960 K,3472K),high color rendering index(Ra=85.5,89)and high lumen efficiency(129 lm/W,117.72lm/W)were obtained,respectively.The results show that(NH4)2Na In F6:Mn⁴⁺and Na3Al F6:Mn⁴⁺are excellent red phosphors for warm white LEDs.3.Ga³⁺-doped K₂Li Al F₆:Mn⁴⁺and Ge⁴⁺-doped Na₂Si F₆:Mn⁴⁺red phosphors were successfully prepared by coprecipitation method.Under blue light excitation,the red light emitting in K₂Li Al_0.4Ga_0.6F₆:0.04Mn⁴⁺and Na₂Si_0.5Ge_0.5F₆:0.06Mn⁴⁺phosphors has high color purity and low correlated color temperature.The variation of zero-phonon line intensity and the shift of the emission peak prove the variation of crystal field environment of K2Li Al1-y Gay F6 and Na2Si1-y Gey F6,respectively.The crystal field strength and the nephelauxetic effect of Mn⁴⁺in K2Li Al0.4Ga0.6F6 and Na2Si0.5Ge0.5F6 matrix materials were analyzed according to the excitation and emission peak energies.The K₂Li Al_0.4Ga_0.6F₆:0.04Mn⁴⁺and Na₂Si_0.5Ge_0.5F₆:0.06Mn⁴⁺red phosphors have good thermal stability.In addition,Na2Si0.5Ge0.5F6:0.06Mn⁴⁺red phosphor also has excellent hydrophobic stability.When K₂Li Al_0.4Ga_0.6F₆:0.04Mn⁴⁺and Na₂Si_0.5Ge_0.5F₆:0.06Mn⁴⁺phosphors were used as red components,the packaged white LEDs have low color temperature(3240 K,3408 K),high color rendering index(Ra=88.1,89.4)and high lumen efficiency(60.93lm/W,112.89 lm/W),respectively.4.A series of Na2GeF6:Mn⁴⁺red phosphors with different morphologies were prepared by coprecipitation method.The effects of different surfactants on the morphology of the samples were analyzed in detail.The optimum doping concentration and concentration quenching mechanism of Mn⁴⁺in Na2GeF6 host were explored.Then,Na₂GeF₆:Mn⁴⁺nanoparticles were converted into Na₂GeF₆:Mn⁴⁺nanofiber film with red-light emission by electrospinning technology.Under the excitation of blue light,the color purity of Na2GeF6:Mn⁴⁺nanoparticles and nanofiber film can reach 91.4%and 80.9%,respectively.Compared with Na2GeF6:Mn⁴⁺nanoparticles,the luminescent intensity of Na2GeF6:Mn⁴⁺nanofiber film decreases slightly.An efficient warm white LED with CCT=2452 K and Ra=85 was obtained by using Na2GeF6:Mn⁴⁺nanofiber film as red light component.5.The BaGeF₆:Mn⁴⁺@PPG-Na GdF₄:Dy³⁺composite phosphors were synthesized by combined coprecipitation with hydrothermal method.PPG can be used as an absorption medium to combine Na GdF4:Dy³⁺nanoparticles with Ba GeF6:Mn⁴⁺phosphor,and effectively improve the luminescence intensity and water stability of Ba GeF6:Mn⁴⁺phosphor.The luminescent properties and energy transfer process of Ba GeF6:Mn⁴⁺@PPG-Na GdF4:Dy³⁺composite phosphors were discussed in detail.Under the excitation of ultraviolet light,red,yellow and blue emission can be obtained simultaneously.By changing the excitation wavelength and adjusting the doping ratio of Mn⁴⁺and Dy³⁺,the composite phosphors can realize multi-color adjustable luminescence.In addition,the energy transfer processes from Gd³⁺to Dy³⁺and Dy³⁺to Mn⁴⁺can be found in the composite phosphor.