Application Of Rare Earth Doped Sulfur Oxide Phosphors In Radiation Warning

X-rays are harmful to human body,but they can not be observed by naked eyes,and are easy to be ignored in the process of use.Therefore,it is very necessary to display the X-rays in the environment and carry out effective protection against them.If a special light-emitting material is developed to mark the area with X-rays,it can serve as a warning for the people in the X-ray environment and take corresponding protective measures,then the X-ray harm can be effectively avoided.Rare earth elements have special 4f electron shell structure and are widely used in the field of luminescence.In this paper,Eu³⁺and Tb³⁺as doping ions were used to synthesize red and green X-ray luminescent materials by solid phase method,respectively.The phase,morphology and luminescent properties of the materials were analyzed,and the feasibility of application of X-ray environmental warning was explored.(1)Two kinds of phosphors,La₂O₃:Eu³⁺and La₂O₃:Tb³⁺,were synthesized and analyzed by mixing La₂O₃ powder with Eu₂O₃ and Tb₄O₇ in a certain proportion at the sintering temperatures of 800?,1000?and 1200?,respectively.The results show that Eu³⁺and Tb³⁺are dissolved into the La₂O₃ matrix lattice in different degrees.The particles sintered at 1200?have irregular morphology and obvious sintering phenomenon,and the particle size is about 1?m.The doping concentration and sintering temperature of rare earth ions Eu³⁺and Tb³⁺have obvious effects on the luminescence intensity under the ultraviolet excitation at 265 nm.With the increase of the doping concentration of rare earth ions(1,3,5,7,9 mol%),the luminescence intensity increased at first and then decreased.The suitable doping concentrations of Eu³⁺and Tb³⁺were 5 mol%and 3 mol%,respectively.La₂O₃:Eu³⁺exhibits Eu³⁺characteristic emission peaks under UV excitation at 265 nm,in which the ⁵D₀-⁷F₂ transition peak is the strongest and the peak wavelength is located at 626 nm.La₂O₃:Tb³⁺shows typical Tb³⁺emission characteristics under 265 nm UV excitation,corresponding to ⁵D₄-⁷F₆,⁵D₄-⁷F₅,⁵D₄-⁷F₄ and⁵D₄-⁷F₆ transitions,respectively.⁵D₄-⁷F₅ transition is the dominant emission and the peak wavelength is 544 nm,which belongs to the green luminescence phosphor.Although the two kinds of rare earth oxide phosphors prepared by this experimental process have certain optical signals under UV excitation,no obvious optical signals were observed for the two kinds of rare earth oxides under low intensity(40 KV,200 m A)X-ray irradiation,which cannot meet the application of highly sensitive luminescence warning under X-ray irradiation.(2)The La₂O₃ powder,sodium carbonate and sulfur powder were mixed with Eu₂O₃ and Tb₄O₇ in a certain proportion,and the method of filling activated carbon in the middle of a double-layer crucible was used to provide the curing conditions and reducing atmosphere.The sintering temperature was 800?,1000?,1200?and 1400?.Rare earth La₂O₂S:Eu³⁺and La₂O₂S:Tb³⁺phosphors were synthesized and analyzed in a box furnace.The results show that the doped ions Eu³⁺and Tb³⁺are dissolved into the La₂O₂S matrix lattice to varying degrees,but the matrix lattice does not change,and the product is a hexagonal phase(space group P3(?)m1).Scanning electron microscopy(SEM)showed that the average particle size of the product prepared at 1200?was about 8.86?m,and it had clear boundary and smooth surface.Under the excitation of 265 nm UV wavelength,the highest peaks of the two phosphors are located in the⁵D₀-⁷F₂ transition at 625 nm and the ⁵D₄-⁷F₅ transition at 544 nm respectively.The doping concentration of rare earth ions Eu³⁺and Tb³⁺has a significant effect on the luminescence performance.With the increase of doping concentration of Eu³⁺and Tb³⁺(1,3,5,7,9 mol%),the luminescence intensity increases at first and then decreases.In this experiment,the suitable doping amount of Eu³⁺is 9 mol%,and that of Tb³⁺is 3 mol%.Sintering temperature also has an effect on the luminescence.The luminescence properties of the products prepared at 1200?are better.The theoretical results show that the concentration quenching phenomenon is the interaction between doped ions.The luminescence warning effect of La₂O₂S:Eu³⁺(Tb³⁺)phosphors under X-ray irradiation was investigated.Different from the results of La₂O₃:Eu³⁺(Tb³⁺)phosphors,La₂O₂S:Eu³⁺(Tb³⁺)phosphors emit bright red and green light under X-ray irradiation of the same intensity(40 KV,200 m A),respectively.It has the research value of X-ray warning application.(3)La₂O₂S:Eu³⁺(Tb³⁺)phosphors were mixed with water-based acrylic resin to prepare La₂O₂S:Eu³⁺(Tb³⁺)fluorescent coatings.The optimum La₂O₂S:Eu³⁺(Tb³⁺)phosphor was 20?30wt%.The La₂O₂S:Eu³⁺(Tb³⁺)phosphors have potential applications in X-ray luminescence warning,and the unique green luminescence of La₂O₂S:Tb³⁺fluorescent coating is more effective in luminescence warning.