Study On Rare Earth Ions Doped Double Perovskite A_ⅰA_ⅱMgB_ⅱO₆:RE³⁺(A_ⅰ=Li⁺,Na⁺;A_ⅱ=Y³⁺,Eu³⁺;B_ⅱ=W⁶⁺,Mo⁶⁺)

In recent years,double perovskite compounds with the general formula（ABO₃）₂ have been widely used as host materials in the field of luminescence due to their unique chemical structures and flexible compositional tunability.In this paper,a typical double perovskite structure A_iA_iiMg B_iiO₆(A_i=Li⁺,Na⁺;A_ii=Y³⁺,Eu³⁺;B_ii=W⁶⁺,Mo⁶⁺)is selected as the matrix material,and trivalent rare earth ions are used as activators.The A_iA_iiMg B_iiO₆:RE³⁺(A_i=Li⁺,Na⁺;A_ii=Y³⁺,Eu³⁺;B_ii=W⁶⁺,Mo⁶⁺;RE³⁺=Eu³⁺,Dy³⁺,Tm³⁺)series luminescent materials structure and luminescence properties are systematically studied by manipulating the type and proportion of matrix cations,the kind and concentration of rare earth ions etc..The main results are as follows:1.The experimental samples were obtained by traditional high temperature solid-phase method.By changing the types and proportions of A_i,A_ii and B_ii cations in A_iA_iiMg B_iiO₆matrix,the effect of cation transformation on A_iA_iiMg B_iiO₆:Eu³⁺(A_i=Li⁺,Na⁺;A_ii=Y³⁺,Eu³⁺;B_ii=W⁶⁺,Mo⁶⁺)series red phosphor luminescence and structure are investigated systematically.This series of phosphors can be effectively excited by near-ultraviolet and blue light sources,and the emission spectra exhibit typical red light of Eu³⁺.The optimal emission position is about 617 nm.The specific work content mainly includes several parts as follows:（1）In the structure of A_iYMg WO₆:Eu³⁺(A_i=Li_xNa_1-x,0≤x≤1),when A_i ions gradually changed from Na⁺to Li⁺,the series of samples kept the single-phase structure and the fluorescence spectra of the samples were almost unchanged.However,the luminescence intensity of the sample increases with the increase of displacement ratio x and reaches the maximum value at x=1.We speculate that this can be attributed to the decrease of lattice symmetry and the distortion of crystal structure when small radius ions gradually replace large radius ions(R⁺_Na=1.39?,R⁺_Li=0.92?);（2）In the Li YMg B_iiO₆:Eu³⁺(B_ii=W_1-yMo_y,0≤y≤1)structure,when the B_ii-site cation gradually changed from W⁶⁺to Mo⁶⁺,the emission spectrum of samples,namely,the red emission at 617 nm of Eu³⁺remains the same.In the excitation spectrum,the excitation band is gradually broadened from the ultraviolet region（250-350 nm）to the near ultraviolet regions（250-400 nm）.This is because the electronegativity of Mo⁶⁺is lower than that of W⁶⁺(Mo⁶⁺:2.16;W⁶⁺:2.36),and the 4d orbital energy level of Mo⁶⁺is lower than the 5d orbital energy level of W⁶⁺,so the charge transfer from O^2-to Mo⁶⁺occurs more easily;（3）In the Na YMg WO₆structure,when the A_ii-site cation Y³⁺is completely replaced by Eu³⁺and the Eu³⁺concentration continues to increase,i.e.Na_1-zEu_1+z/3Mg WO₆,the sample still maintains the single-phase structure and the fluorescence spectrum remains unchanged.At this moment,the excess Eu³⁺will gradually replace Na⁺.And the corresponding cation vacancy defects will appear to maintain the charge balance.Lattice distortion will reduce the symmetry of the crystal structure and the luminescence intensity of the sample will be enhanced.In addition,this series of red phosphors has good temperature properties and can still maintain 74.2%of the room temperature luminescence intensity at 200°C.2.A series of Dy³⁺,Tm³⁺single and co-doped Li YMg WO₆:Dy³⁺/Tm³⁺(LYMW:Dy³⁺/Tm³⁺)luminescent samples were prepared by high temperature solid-phase method.The results of structural analysics show that the samples belong to the monoclinic system and the space group is P2₁.The excitation spectra of the samples are composed of matrix charge transfer band(W⁶⁺→O^2-)and characteristic excitation of the doped luminescence centers,indicating that these phosphors can be excited effectively by ultraviolet and near ultraviolet.The LYMW:Dy³⁺emits yellowish-white light,which corresponds to the two characteristic transitions of Dy³⁺（⁴F9/2→⁶H15/2（474 nm）and ⁴F9/2→⁶H13/2（575 nm））.The intensity reaches the maximum when the doping concentration of Dy³⁺is 6%.For LYMW:Tm³⁺,blue light is derived from the characteristic transitions ¹G4→³H6and ¹D₂→³F₄of Tm³⁺.Whenλex=358 nm,the optimal doping concentration of Tm³⁺is 4%.For the sake of compensating the blue light composition of LYMW:Dy³⁺,Tm³⁺was introduced.The results show that the white light properties of Li YMg WO₆:Dy³⁺can be improved by co-doping Tm³⁺,which makes it gradually move to the ideal white light region.Energy transfer also occurs from Tm³⁺to Dy³⁺,which greatly boosts the luminescence intensity of the sample.