Study On The Self-reduction Mechanism And Luminescence Properties Of Eu²⁺-Eu³⁺ Doped Phosphate Composites Induced By Synergistic Effect

In this paper,a series of Eu²⁺-Eu³⁺excited phosphate fluorescent materials were synthesized by high temperature self-reduction method in air atmosphere.The properties of the samples were characterized by thermogravimetry(TGA),X-ray diffraction(XRD),fluorescence spectrum,infrared spectrum(IR),scanning electron microscope-energy spectrum(SEM-EDS)and color coordinate(CIE).It is found that the color adjustment of phosphor can be realized through the following three ways.One is to adjust the color of phosphor through single ion doping,controlling the doping content of Eu³⁺and combining Eu²⁺generated by self-reduction,and spatial color mixing.The second is to influence the structure of phosphor by doping some network forming bodies and to regulate the self-reduction degree of trivalent rare earth ions by doping monovalent alkaline earth metal ions.Finally,the luminous color of phosphor is adjusted.Third,through multi-ion doping,different rare earth ions can exhibit different colors under the excitation of ultraviolet light,and under the condition of multi-ion co-doping,there will be energy transfer phenomenon between different ions.By controlling the doping content of different ions,the luminous color of phosphor can finally be adjusted.(1)Sr BPO₅:Eu²⁺-Eu³⁺phosphors were synthesized by traditional solid self-reduction reaction in air atmosphere.The properties of the samples were studied.The results show that there is no effect on the main structure of the matrix with different concentrations of Eu doping.Eu mainly exists in both bivalent and trivalent forms in the matrix.The emission peaks at 403 nm are attributed to the typical 5d-4f transition of Eu²⁺,while the emission peaks at 597 nm and 620 nm are attributed to the characteristic ⁵D₀-⁷F_1,2 transition of Eu³⁺.By controlling the doping amount of Eu³⁺,the color tone of phosphor can be macroscopically controlled from blue to purple.Therefore,we can adjust the relative luminous intensity between Eu²⁺and Eu³⁺by controlling the doping concentration of Eu,thus realizing colorful emission of phosphors.(2)A series of Sr₂P₂O₇:Eu²⁺-Eu³⁺phosphors were synthesized by high temperature solid phase method.The experimental results show that the existence of different network forming bodies(SiO₂,Ge O₂)has certain influence on the microstructure and luminescent properties of phosphors.Interestingly,the addition of SiO₂ and Ge O₂ can significantly improve the luminescence intensity of Eu²⁺.By introducing Li⁺or Na⁺to compensate vacancy defects,the purpose of coordinating the luminous color of phosphor can be achieved.The Eu²⁺/Eu³⁺co-activated Sr₂P₂O₇phosphor prepared in this paper has excellent luminescent properties and can be adjusted through various channels.(3)A series of SrMg₂(PO₄)₂:Eu²⁺-Eu³⁺,Dy³⁺phosphors were synthesized by high temperature solid phase method in air.The structure and luminescent properties of the samples were studied in detail by X-ray diffraction(XRD).SrMg₂(PO₄)₂:Eu²⁺-Eu³⁺samples can emit tunable blue-purple light by controlling the ratio of Eu and Dy doping concentrations under 340 nm excitation.However,Dy³⁺exhibits typical blue and yellow luminescence under the excitation of 350 nm.By comparing the fluorescence spectra of Dy and Eu co-doped systems,the energy transfer from Eu³⁺to Dy³⁺in Dy and Eu co-doped systems was found.In addition,the color coordinates of the International Lighting Committee(CIE)show that the luminous area of phosphor is concentrated in the blue-purple area.(4)A series of Mg₂₁Ca₄Na₄(PO₄)₁₈:Eu²⁺-Eu³⁺phosphors are successfully synthesized by high temperature solid state method in air atmosphere.The phase structures and luminescent properties of the samples are studied in detail.Phosphors exhibit strong visible light emission under different wavelengths of UV excitation.By harmonizing the doping concentration of Eu³⁺to adjust the relative luminescence intensity of Eu²⁺and Eu³⁺,colorful emission of phosphors can be achieved.