Synthesize New Phosphate Phosphors Through Energy Transfer Design

In recent years,the world’s energy resources have become increasingly scarce and environmental pollution has become increasingly serious.The research and development of new energy materials has become urgent.For the lighting industry,traditional lighting methods have low luminous efficiency and high energy consumption,which have been unable to meet people’s increasing demand for luminous performance,and it has become urgent to find new high-efficiency,energy-saving and environmentally-friendly lighting materials.With the support of various policies for the development of green energy-saving devices,the lighting industry is also rapidly advancing on the speedboat of policies.The new LEDs stand out with the characteristics of high efficiency,green environmental protection,and adjustable luminescence,and cater to the needs of the development of the times.High-efficiency and energy-saving materials provide a new approach.At present,there are two main ways to improve the luminous efficiency of new LED phosphors:（1）Through the ion pair substitution strategy,other ions are introduced into the known matrix to change the crystal phase of the phosphor,so as to optimize the luminous performance and the spectrum of the phosphor.（2）Through the energy transfer between the sensitizer and the activator,the spectral control of the phosphor is realized.In this paper,three new phosphate phosphors of Sr_5-2x-yTb_xNa_x（PO₄）₃Br:y Eu²⁺,Sr_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺and Ba_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺are prepared.All of these three phosphate phosphors were designed according to the Eu→Tb energy transfer mechanism.By adjusting the doping concentration ratio of different ions,the luminous intensity of the phosphor is significantly improved,and the luminescence color is successfully regulated.The luminescence characteristics,concentration quenching and fluorescence lifetime of the tree phosphors are studied in detail.The mechanism of Eu→Tb energy transfer is analyzed and explained.The specific work is as follows:（1）The structure and luminescence properties of Sr_5-2x-yTb_xNa_x（PO₄）₃Br:y Eu²⁺（0≤x≤0.60,0≤y≤0.20）phosphate phosphors are studied.XRD research shows that the[Na⁺,Tb³⁺]ion pair and Eu²⁺successfully enter the matrix Sr₅（PO₄）₃Br,and a pure phase hexagonal phosphor is obtained.Due to the energy transfer between Eu and Tb,the luminous intensity of Eu-Tb co-doped samples is significantly improved compared with single-doped Tb³⁺phosphors.By changing the concentration of the[Na⁺,Tb³⁺]ion pair,the emission color of the Sr_5-2x-yTb_xNa_x（PO₄）₃Br:y Eu²⁺（0≤x≤0.60,0≤y≤0.20）phosphor can be controlled.Studies show that Sr_5-2x-yTb_xNa_x（PO₄）₃Br:y Eu²⁺（0≤x≤0.60,0≤y≤0.20）is a new luminous material with high efficiency,tunable spectrum and potential application value in white LED.（2）The structure,concentration quenching mechanism and luminescence properties of Sr_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺（0≤x≤0.60,0.005≤y≤0.10）phosphate phosphors were studied.XRD data show that the XRD peaks of all the phosphor samples can match with the standard card（PDF#87-0120）of Sr₅（PO₄）₃Cl,indicating that the crystal structure was not changed by the introduction of doped ions.The optimal doping concentration of Eu²⁺is y=0.025 while the optimal doping concentration of[Na⁺,Tb³⁺]ion pair is x=0.50 in Sr_5-2x-yTb_xNa_x（PO₄）₃Br:y Eu²⁺phosphor.The phosphors prepared by chemical unit substitution strategy exhibit broad excitation spectra in the range of 200-450 nm and broad emission band,which can be well matched with near-ultraviolet LED chips.In summary,Sr_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺is a new luminescent material with high efficiency,adjustable spectrum,and potential application value in white light LEDs.（3）The concentration quenching,luminescence properties and energy transfer mechanism between Eu²⁺and Tb³⁺in Ba_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺（0≤x≤0.60,0≤y≤0.09）phosphors were studied.The results show that the emission spectra of Ba_3.97Tb_0.50Na_0.50（PO₄）₃Cl:0.03Eu²⁺phosphors not only contain the emission band of Eu²⁺but also the emission band of Tb³⁺under 354 nm UV excitation.CIE color coordinate display that the luminous color of Ba_4.97-2xTb_xNa_x（PO₄）₃Cl:0.03Eu²⁺phosphor is regulated by changing the concentration of[Na⁺,Tb³⁺]ion pair.The energy transfer mechanism of Eu→Tb can be explained as since the energy level of the 4f⁶5d¹ excited state of Eu²⁺is close to the energy level of the ⁵D₄ excited state of Tb³⁺,the electrons in Eu²⁺excited to the 4f⁶5d¹excited state will transfer part of the energy to Tb³⁺,thereby exciting more electrons of Tb³⁺from ground state to the excited state,so the Tb³⁺luminescence intensity is enhanced.The above research results show that Ba_5-2x-yTb_xNa_x（PO₄）₃Cl:y Eu²⁺is a new luminescent material with high efficiency,adjustable spectrum and potential application value.