Preparation And Luminescence Properties Of Double Perovskite Red Phosphors For White LED

This paper is mainly aimed at the problems of poor thermal stability and low color purity in current commercial red phosphors,and attempts to study a new and effective red phosphor.The details are as follows:1.Preparation of Tb³⁺,Eu³⁺ion co-doped NaLaMgWO₆ phosphors and study of their luminescence propertiesA series of Tb³⁺and Eu³⁺co-doped NaLaMgWO₆ phosphors were prepared by the traditional high-temperature solid-phase method.X-ray diffraction,electron scanning microscope,fluorescence spectrum analyzer and other testing methods were used to systematically study the sample’s phase structure,particle morphology,photoluminescence performance and thermal stability.XRD results show that the crystal structure of NaLaMg WO6:Tb³⁺,Eu³⁺phosphors is a single double perovskite structure,which belongs to the C2/m space group.Rietveld refinement results show that Tb³⁺and Eu³⁺ions can effectively replace La³⁺to form substitutional doping,and have less effect on the phase of NaLaMgWO₆.The results of luminescence research show that there is an energy transfer phenomenon between Tb³⁺and Eu³⁺in NaLaMgWO₆ phosphors co-doped with Tb³⁺and Eu³⁺.With the change of the ratio of Eu³⁺and Tb³⁺ions,the color of NaLaMgWO₆:Tb³⁺,Eu³⁺Green light becomes red light,and its corresponding CIE color coordinate changes from（0.293,0.586）to（0.648,0.351）.In addition,it was confirmed by fluorescence lifetime testing that the energy transfer process from Tb³⁺to Eu³⁺in NaLaMgWO₆:Tb³⁺,Eu³⁺phosphors was completed through dipole-quadrupole interaction.Finally,the thermal stability of NaLaMgWO₆:Tb³⁺,Eu³⁺phosphors was characterized.The results show that NaLaMgWO₆:Tb³⁺,Eu³⁺phosphors have good thermal stability,and the thermal activation energyΔE value is 0.302 e V.2.Study on the Effect of Zn²⁺Doping on the Luminescent Properties of NaLaMg WO6 Red PhosphorNaLaMg_1-xZn_xWO₆:Eu³⁺series red phosphors were successfully prepared by high temperature solid phase method.The results show that when the doping concentration of Zn²⁺ions is less than 0.3,NaLaMg_1-xZn_xWO₆:Eu³⁺phosphor with single-phase dual perovskite structure can be obtained.Under the condition of a single phase,the doping of Zn²⁺ions can effectively improve the luminous intensity and thermal stability of the phosphor.The optimal doping concentration of Zn²⁺is 0.3.At this doping concentration,the thermal activation energy of NaLaMg_0.7Zn_0.3WO₆:Eu³⁺phosphor changes from0.333e V to 0.303e V,and the thermal stability is significantly improved.Finally,the influence of the doping concentration of Eu³⁺on its luminescence performance was studied.The results show that with the change of the doping concentration of Eu³⁺ions,the luminous intensity of the phosphor first increases and then decreases.The optimal doping concentration of Eu³⁺ions is 0.5,and the corresponding CIE color coordinates are（x=0.6228,y=0.3710）.3.Preparation of（Na,K）（La,Gd）MgWO₆:Eu³⁺Red Phosphor and Its Luminescent PropertiesNa La_0.9-xGdx MgWO₆:0.1Eu³⁺series red phosphors were successfully synthesized by the traditional high-temperature solid-phase method.XRD studies show that when the doping concentration of Gd³⁺ions is less than 0.6,a single-phase composite structure of Na La_0.9-xGd_xMgWO₆:0.1Eu³⁺red phosphor can be obtained.Excited by near-UV light at395nm,Na La_0.9-xGd_xMgWO₆:0.1Eu³⁺phosphor emits red light mainly at 617nm.In addition,the temperature dependence curve of the phosphor shows that the incorporation of Gd³⁺can effectively improve the thermal stability of the phosphor,and its thermal activation energy is 0.284e V.KLa_1-xMgWO₆:x Eu³⁺phosphor was successfully prepared by the traditional high-temperature solid-phase method.XRD results show that KLa MgWO₆ phosphor also has a monoclinic double perovskite structure.PL spectrum tests show that under near-ultraviolet and blue light excitation,the phosphor will emit red light mainly at 617nm,which corresponds to the ⁵D₀→⁷F₂ transition of Eu³⁺,and the optimal doping concentration of Eu³⁺ions is 0.4.In addition,in order to further analyze the transition characteristics of Eu³⁺in KLa_1-xMgWO₆:x Eu³⁺phosphors,J-O theory was used to calculate radiative transition parameters such as Eu³⁺radiation transition rate and fluorescence branch ratio（β）in this phosphor.The results show that the fluorescence branching ratioβof the ⁵D₀→⁷F₂ transition of Eu³⁺is larger than that of other transitions,which can indicate that Eu³⁺ion occupies a non-centrosymmetric lattice position in the double perovskite matrix.