Sol-gel Method To Prepare Rare Earth-doped Silicate-based Phosphors And Research On Their Luminescence Properties

As a new generation of green lighting source,white LED has the advantages of easy and convenient,long life cycle,high luminous efficiency and low cost.Currently,the conversion of single-chip phosphors is the main way to achieve white LEDs.Therefore,the luminescent properties of the phosphor have an important influence on the luminescence of the white LED.In addition,the luminescent properties of the phosphor are closely related to the physicochemical properties of the matrix material.Therefore,it is very important to choose a material with good physicochemical properties as the matrix of the phosphor.The silicate has the advantages of stable physical and chemical properties,low cost and easy availability of raw materials,simple synthesis process,and the like,and is an ideal matrix material for rare earth phosphors.Studies on rare earth phosphors based on silicates have often been reported.Due to its stable crystal structure,silicate has important application value in white LED and display lighting.Three rare earth phosphors of Eu³⁺,Tb³⁺,Ce³⁺rare earth ion single doping and double doping M₃MgSi₂O₈?M=Sr,Ba?silicate were prepared by sol-gel method.The effects of calcination temperature and rare earth ion doping concentration on its luminescence properties were studied,and the interaction mechanism between rare earth ions was discussed.The main research contents of this paper are as follows:First,Sr₃MgSi₂O₈:Eu³⁺red phosphor was synthesized by sol-gel method.The effects of calcination temperature on the morphology and luminescence properties of the samples were investigated.When the calcination temperature is 1150°C,the obtained phosphor has the largest specific surface area of 90.21 m²/g;At 394 nm excitation wavelength,all samples showed strong emission peaks at 614 nm and 702 nm,corresponding to the ⁵D₀?⁷F₂ and⁵D₀?⁷F₄ transitions of Eu³⁺,which belonged to red emission.The luminescence intensity of Sr₃MgSi₂O8:Eu³⁺red phosphors obtained at the calcination temperature of 1150°C is the highest when the luminescence intensity of the samples treated with different calcination temperatures were compared.That is,the optimum calcination temperature is 1150°C.Second,A single phase multi-color phosphor Sr_3-x-yMgSi₂O₈:xEu³⁺,yTb³⁺?x=0%?1%?2%?4%?6%?8%,y=0%?0.5%?1%?2%?4%?6%?8%?was synthesized by sol-gel method.The relationship between the doping concentration of Eu³⁺and Tb³⁺and the luminescence properties was studied.It is found that Tb³⁺has a sensitizing effect on the luminescence of Eu³⁺,and Eu³⁺has a weakening effect on the luminescence of Tb³⁺,that is,there is a unidirectional energy transfer of Tb³⁺?Eu³⁺.The energy transfer efficiency of Tb³⁺?Eu³⁺in Sr_2.9MgSi₂O₈:8%Eu³⁺,2%Tb³⁺was obtained by fitting the fluorescence lifetime curve equation was 35.98%.Through the Forster-Dexter theory,the energy transfer mechanism of Tb³⁺?Eu³⁺was studied and it was found that the energy transfer was achieved by electric dipole-dipole interaction.Among them,the Sr_2.95MgSi₂O₈:3%Eu³⁺,2%Tb³⁺phosphor has a thermal activation energy Ea value of 0.309 eV,showing good thermal stability.Third,the Tb³⁺,Ce³⁺co-doped Ba₃MgSi₂O₈:xCe³⁺,yTb³⁺phosphors were prepared by sol-gel method.The relationship between the doping concentration of Tb³⁺and Ce³⁺ions and their luminescence properties was studied.The optimum doping concentration of Tb³⁺was8%.With the increase of Ce³⁺concentration,the emission peak?544nm?corresponding to Tb³⁺in the phosphor Ba_2.94-xMgSi₂O₈:xCe³⁺,6%Tb³⁺first increases and then decreases.When the doping concentration of Ce³⁺is 8%,The luminescence intensity of Tb³⁺is the strongest.In the phosphor Ba_2.92-yMgSi₂O₈:8%Ce³⁺,yTb³⁺,the emission peak corresponding to Ce³⁺decreases gradually with the increase of Tb³⁺doping concentration.That is,in the phosphors Ba₃MgSi₂O₈:xCe³⁺,yTb³⁺,there is energy transfer of Ce³⁺?Tb³⁺.At the same time,The energy transfer efficiency of Ce³⁺?Tb³⁺in Ba_2.84MgSi₂O₈:8%Tb³⁺,8%Ce³⁺phosphor was calculated by fitting the fluorescence lifetime curve equation was 34.64%.The energy transfer mechanism of Ce³⁺?Tb³⁺was studied and found to be energy transfer through exchange.The energy transfer mechanism of Ce³⁺?Tb³⁺was studied and found to be energy transfer through exchange.The thermal activation energy Ea value of the phosphor Ba_2.84MgSi₂O₈:8%Tb³⁺,8%Ce³⁺was 0.113 eV.These above research results show that the luminescence properties of the phosphor can be improved by optimizing the calcination temperature and other process conditions in the preparation process.At the same time,among the three phosphors prepared in this paper,Sr_3-x-yMgSi₂O₈:xEu³⁺,yTb³⁺phosphors are not only tunable in color,but also have good thermal stability.Sr_3-x-yMgSi₂O₈:xEu³⁺,yTb³⁺phosphors have the most application value compared to the other two phosphors.