Synthesis And Luminescence Properties Of Sr₃?VO₄?₂:Eu³⁺ And NaSrVO₄:Eu³⁺ Red Phosphors

In recent years,White light emitting diodes?LED?are widely used in many fields due to their high photosynthetic efficiency,low energy consumption,long lifetime and high brightness.The main method to generate white LED is combining a blue LED chip with yellow phosphor.However,the deficiency of red emission degrades the color rendering index and limit their use to high color temperature.Therefore,developing a red phosphor with high efficiency and high stability is the key to the development of white LED industry.In this paper,Sr₃?VO₄?₂:Eu³⁺ and NaSrVO₄:Eu³⁺ red emission phosphors were synthesized by citric acid complex combustion method.The samples were characterized by X-ray diffraction?XRD?,Scanning Electron Microscope?SEM?and fluorescence spectrophotometer.The optimum synthetic process conditions were determined.Moreover,the phase,luminescent properties,energy transfer and doping modification were also investigated.The Sr₃?VO₄?₂:Eu³⁺ phosphor with high purity and excellent luminescence properties can be obtained at 800oC for 60 min in conjunction with the citric acid dosage n?CA?=2n?NH₄VO₃?+1.6n?Mn+?.The sample emits red light with a dominant wavelength of 617 nm under the excitation of 393 nm.The concentration of rare earth ions has an important influence on the luminescence properties.The emission intensity increases with Eu³⁺ concentration increase,and the best emission intensity can be obtained at 12mol%,then the emission intensity declined.When doping with alkali metal ions as the charge compensation,the impact of the luminescence properties on Sr₃?VO₄?₂:Eu³⁺ by the amount and the type of the charge compensation were investigated.The result showed that the charge compensation such as Li+,Na+,K+ ions can promote the Eu³⁺ electronic transition effectively.Doping Na+ as the charge compensation,while the concentration was same as Eu³⁺,the Sr₃?VO₄?₂:Eu³⁺ showed the highest red light emission intensity.While doping the equal amount Li+,Na+,K+ with Eu³⁺ as the charge compensation,samples emission intensity enhanced significantly with the ionic radius decreased and the emission spectra shifted to the short wavelength.On the basis of these studies,a novel Eu³⁺ activated alkali metal alkaline metal vanadate phosphor system was synthesized by citric acid complex combustion method.Under the same reaction time and the same amount of citric acid in conjunction with the reaction temperature of 900°C,the high crystallinity of the NaSrVO₄:Eu³⁺ can be synthesized,which belongs to the monoclinic crystal system,P21/n space group.Under an excitation of 393 nm.NaSrVO₄:Eu³⁺ showed a bright red emission,and the most intense peak located at 625 nm,which belongs to the 5D0?7F2 electric dipole transition of Eu³⁺.When the Eu³⁺ doping concentration was 15mol%,the red emission intensity of NaSrVO₄:Eu³⁺ was strongest,followed by concentration quenching,luminous intensity decreased.Bi³⁺ ion doping significantly enhanced the luminescence intensity of NaSrVO₄:Eu³⁺ red phosphors.Bi³⁺ ion doping was studied with optimized Eu³⁺ doping concentration of 15mol% as standard sample.With the increase of Bi³⁺ doping amount,the red emission of the sample gradually increased.The Bi³⁺ as the sensitizer had energy transfer with the Eu³⁺ ion.When the concentration of Bi³⁺ reached at 3mol%,the relative emission peak intensity of the maximum at the sample color coordinates was x =0.658,y =0.342,similar to a standard red color coordinates?x = 0.67,0.33?,which is a potential application of the white LED with a red phosphor.