Synthesis And Luminescence Enhancement Of Ca₃Sr₃?VO₄?₄ Red Phosphor By Doping Re³⁺

In recent years,White light emitting diodes?WLEDs?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.Vanadate is becoming increasingly popular in the systhesis of red-emitting phosphors because if it has excellent chemical stability,thermosatbility,crystalinity and visible light transmittance.Fuethermore,the existing of effective energy transfer between rare-earth luminescence center and VO₄^3-makes the vanadate is a promising matrix material in the synthesis of red-emitting phosphor.In this paper,Ca₃Sr₃?VO₄?₄:Eu³⁺,RE³⁺?RE=Sm?La?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 Ca₃Sr₃?VO₄?₄:Eu³⁺phosphor with high purity and excellent luminescence properties can be obtained at 900oC for 60 min.all Ca₃Sr₃?VO₄?₄ synthesized phosphors synthesized at temperatures greater than 700?exhibited the same crystal structure,namely,the standard rhombohedral structure of Ca₃Sr₃?VO₄?₄.The sample emits red light with a dominant wavelength of 619 nm under the excitation of 393 nm and 464 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 5 mol%,then the emission intensity declined.Sm³⁺and La³⁺ion doping significantly enhanced the luminescence intensity of Ca₃Sr₃?VO₄?₄:Eu³⁺red phosphors.Sm³⁺ion doping was studied with optimized Eu³⁺doping concentration of 5 mol%as standard sample.With the increase of Sm³⁺doping amount,the red emission of the sample gradually increased.The Sm³⁺as the sensitizer had energy transfer with the Eu³⁺ion.When the concentration of Sm³⁺reached at 9 mol%,the relative emission peak intensity of the maximum at the sample color coordinates was?x=0.6595,y=0.3402?,similar to a standard red color coordinates?x=0.67,y=0.33?,which is a potential application of the white LED with a red phosphor.Co-doping with La³⁺significantly improved the emission intensity of Ca₃Sr₃?VO₄?₄:Eu³⁺red phosphors.The optimum luminescence property of the phosphor was observed at Eu³⁺and La³⁺concentrations of 5%and 6%,respectively.Moreover,co-doping with La³⁺also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃?VO₄?₄:Eu³⁺phosphor.The CIE chromaticity coordinate of Ca₃Sr₃?VO₄?₄:0.05Eu³⁺,0.06La³⁺is closer to the NTSC standard for red phosphors than other commercial phosphors.The phosphors synthesized herein can be considered promising red-emitting phosphors for applications in white-light-emitting diodes under the irradiation of blue chips and the near-UV LED chips.On the basis of these studies,when doping with alkali metal ions as the charge compensation,the impact of the luminescence properties on Ca₃Sr₃?VO₄?₄:Eu³⁺,Sm³⁺and Ca₃Sr₃?VO₄?₄:Eu³⁺,La³⁺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 ⁵D₀?⁷F₂ electronic transition of Eu³⁺effectively.Doping Li⁺as the charge compensation,while the concentration was same as Eu³⁺,the Ca₃Sr₃?VO₄?₄:Eu³⁺,Sm³⁺and Ca₃Sr₃?VO₄?₄:Eu³⁺,La³⁺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.