Preparation And Fluorescence Properties Of High-coordination Molybdotungstate System Red Phosphors For White Light LEDs

White light-emitting diode(LED)is considered as one of the most promising lighting sources in the 21st century because of its more space-saving,larger brightness,less energy consumption,longer service life and higher color contrast than traditional light sources.However,the present problem is that white LED lacks color richness.The existing blue or near ultraviolet LED chip excitation red phosphor luminous efficiency is low.people are forced to find a new substrate-fluorescent powder with high absorption efficiency,high brightness red emission and satisfactory stability in the near ultraviolet region.The preparation conditions of Eu³⁺ion-activated molybdate and tungstate phosphors are simple,the cost of raw materials is low,and the chemical stability is good,which has become the focus of current research on red phosphors.The charge transfer band of tungstate is located at 250-350 nm,and the phosphors with part of W replaced by Mo have good absorption in the near-ultraviolet region.With the increase of O/M(M=W or Mo)coordination number ratio,the bond energy between M and O decreases,and the excitation band tends to redshift to near ultraviolet region and blue region.Therefore,molybdate is often selected as one of the main fluorescent materials for the synthesis of efficient red phosphors.In this paper,Ba₂Gd_0.67W_1-xMo_xO₆:Eu³⁺and A₂W_1-xMo_xO₅:Eu³⁺(A=Ba,Sr)series phosphors were prepared,the research results are as follows:1.Ba₂Gd_0.67W_1-xMo_xO₆:Eu³⁺phosphors with cubic double perovskite structure were synthesized in this paper.The effects of Eu³⁺on phosphors with different sites A=Ba²⁺,B=Gd³⁺substitution,Eu³⁺doping amount and charge compensator on phosphors were explored.Under the excitation of UV,the main emission peak was 596nm,and the luminescence intensity of Eu³⁺doped at A site was higher than that of B site.The best optimal doping amount of Eu³⁺was 0.1,and the optimal charge compensation agent was Li.2.The effect of Mo/W ratio on the structure and properties of Ba₂Gd_0.67WO₆:Eu³⁺phosphors were investigated.The phase of the material remains unchanged,the excitation spectrum and absorption spectrum were red-shifted,and the excitation band was broadened from 350 nm to 425 nm.Under the excitation of 395 nm,the fluorescence intensity reaches the highest at 596 nm(⁵D₀?⁷F₁)when optimal Mo:W ratio was 2:3,and its color coordinates are(0.61,0.39).When the temperature was from room temperature to 573 K,the relative emission intensity was 50%of the room temperature,and the sample changes from orange-red to orange.3.A₂WO₅:Eu³⁺(A=Ba,Sr)series phosphors were prepared by high-temperature solid-phase method.By exploring the effects of synthesis temperature and different charge compensation agents on A₂WO₅:Eu³⁺(A=Ba,Sr)phosphors,the optimal synthesis temperature of Ba₂WO₅ phosphor was 1100°C,and the optimal charge compensation agent was Li;the optimum synthesis temperature of Sr₂WO₅ phosphor was 1150°C,and the optimum charge compensation agent was K.4.The effect of Mo/W ratio on A₂W_1-xMo_xO₅:Eu³⁺(A=Ba,Sr)phosphors were investigated.The phases of the materials remain unchanged.The excitation spectrum was red-shifted,and the charge transfer band was broadened from 350 nm to 425 nm.The band gap of Ba₂WO₅:Eu³⁺decreased from 3.72 e V to 2.94 e V,and band gap of Sr₂WO₅:Eu³⁺decreased from 2.93 e V to 2.55 e V.Under the excitation of?_ex=395 nm,When the optimal Mo/W ratio of Ba₂W_1-xMo_xO₅:Eu³⁺is 2:3,the fluorescence intensity reached the highest at 596 nm(⁵D₀?⁷F₁),which showed orange-red light emission,and the color coordinate was(x=0.60,y=0.40).When the optimal Mo/W ratio of Sr₂W_1-xMo_xO₅:Eu³⁺was 3:7,the fluorescence intensity reached the highest at 616 nm(⁵D₀?⁷F₂),which showed red light emission,and the color coordinate was(x=0.66,y=0.35).