Properties Of Double Perovskite A₂B?Mo,W?O₆:Eu³⁺,Na⁺ Phosphors For White LED

White Light Emitting Diodes?WLEDs?has become the fourth generation of solid-state lighting source and opened up a new era of green lighting for its small volume,high luminous efficiency,energy saving and long life time.However,compared with blue or green phosphors,the luminescent performance of currently commercial red phosphors is worse.Therefore,the study of novel high-efficient red phosphor which can well match UV LED chip well with high color rendering and high performance for white LED,was urgent and of great practical significance.The double perovskite red phosphor Sr₂CaMoO₆:Eu³⁺was synthesized by the multi-step conventional high-temperature solid-state reaction?first calcined at 700^o C for 1h,then heated to 1050^oC for 2 h,finally to 1300^oC for 4 h?.XRD analysis results indicated that the prepared phosphors can be assigned to orthorhombic double perovskite structure in space group of Pmm2 while PL results showed that Sr₂CaMoO₆:Eu³⁺phosphors can be efficiently excited by near-ultraviolet excitation?399nm?,performing a strong orange-red luminescence.The influence of different charge compensators?M=Li⁺,Na⁺,K⁺?on the luminescence of the sample Sr₂Ca_0.9Eu_0.1MoO₆ was systematically investigated.Na⁺was selected as the optimal charge compensator for this system.Eu³⁺/Na⁺were co-doped at the A and B site of Sr₂CaMoO₆ phosphors respectively.The results of XRD and Raman spectroscopy indicated that Eu³⁺/Na⁺was doped in the A and B site of the system in stoichiometric ratio.Though the fluorescence emission intensity when Eu³⁺/Na⁺doping at the A site is much lower than the situation at B site,A site doped phosphors emit intense red light at 617nm under near-ultraviolet excitation.When Eu³⁺/Na⁺were co-doped in Sr_2-2xEu_xNa_xCaMoO₆ system,the quenching concentration of Eu³⁺was observed up to 15mol%.The theoretical quenching concentration and quenching mechanism were discussed herein.The quenching mechanism of Eu³⁺emission of Sr₂CaMoO₆ matrix is due to dipole-dipole?d-d?interaction.Moreover the effect of different W/Mo content on the structure and luminescent properties of the phosphors were investigated.The optimal photoluminescent intensity was obtained when W/Mo ratio was 9:1,of which the CIE chromaticity coordinate reaches?0.663,0.3368?,very close to the NTSC standard values.The experimental results classify the Sr_2-2xEu_xNa_xCa(W_1-yMo_y)O₆ phosphors as promising candidates for red emission of NUV excited WLEDs.Then the energy transfer mechanism have been explained in detail.The absorption spectrum was measured by UV diffuse reflectance spectroscopy.The absorption band of the matrix Sr₂CaMoO₆ was calculated to be2.94ev and the energy level diagram of the energy transfer process of Sr₂CaMoO₆:Eu³⁺under ultraviolet light?399nm?excitation was plotted.On the basis of the research mentioned before,the A₂BMoO₆:Eu³⁺,Na⁺(A=Sr²⁺,Ba²⁺;B=Ca²⁺,Mg²⁺,Zn²⁺)systems with different crystal structures by using the ratio of electric/magnetic dipole transition as a fluorescent probe were also investigated in the present work.The relation between the ratio of the electric dipole transition and the magnetic dipole transition of the fluorescence emission spectrum and the tolerance factor after Na⁺/Eu³⁺being doped at A,B-site of the orthogonal system?Sr₂CaMoO₆?,the tetragonal system?Sr₂ZnMoO₆?,and the cubic system?Ba₂CaMoO₆,Ba₂ZnMoO₆,Ba₂MgMoO₆?was preliminarily summarized.