Preparation And Characterization Of Rare Earth Doped Core-shell Luminescent Materials

In this paper,SiO₂@La PO₄:Ce³⁺/Tb³⁺was prepared by sol-gel method.NaYF₄:Yb³⁺/Er³⁺and Fe₃O₄@mSi O₂@NaYF₄:Yb³⁺/Er³⁺rare earth-doped phosphors were prepared by thermal decomposition method.The samples were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,x-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?,fluorescence spectrophotometer?PL?to characterize the materials.The best preparation conditions were determined through repeated experiments.The samples were doped with rare earth elements to study the luminescent properties of the system in order to obtain the core-shell luminescent materials with controlled morphology and excellent performance.The main contents of this paper are as follows:?1?SiO₂@LaPO₄:Ce³⁺/Tb³⁺core-shell phosphor was prepared by sol-gel method using Ln?NO₃?₃·6H₂O and NaH₂PO₄ as raw materials.The effects of reaction time,calcination temperature and SiO₂ size on the morphology,crystal structure and luminescence properties of the samples were discussed in details.The experimental results were as follows.When the reaction time is 4 h,the calcination temperature is800?and the amount of tetraethyl orthosilicate is 3 m L,the monodispersed phosphor with the best core-shell structure can be obtained.The amount of tetraethyl orthosilicate determines the size of SiO₂ in the core-shell structure.The size of SiO₂obtained at the dosage of 3 m L is 370 nm,and the luminescence performance of the sample is the best.The calcination temperature plays a key role in the luminescence properties of the sample.With the increase of calcination temperature,the crystallinity of the sample gradually increased.The luminescence intensity of the sample decreased due to the change of sample size and surface morphology after 800?.The luminescent intensity of SiO₂@LaPO₄:Ce³⁺/Tb³⁺core-shell phosphors can reach 71.25%of that of LaPO₄:Ce³⁺/Tb³⁺phosphor at 800?.?2?NaYF₄:Yb³⁺/Er³⁺upconverting nanoparticles?UCNPs?were prepared using rare earth trifluoroacetate RE?CF₃COO?₃ and sodium trifluoroacetate as precursors in the solvent of oleic acid?OA?,oleylamine?OM?and octadecene?ODE?by thermal decomposition method.In the experiment,four basic conditions of different experimental reaction temperature,experimental reaction time,experimental solvent composition and rare earth ion doping concentration were determined,respectively.The effects of these four conditions on the luminescent properties of the product were studied.The results are as follows.When the reaction temperature is 300?,the reaction time is 1.5 h,the size of the obtained sample is about 30 nm,the size is uniform and dispersed uniformly.The structure of the sample is a mixed phase of tetragonal phase and hexagonal phase,the intensity of the sample is the highest,and it emits orange-red light.When the solvent composition is OA:OM:ODE=1:0:1,the luminescent property of the sample is the best,and emits bright green light.When the solvent concentration of doped ions Yb³⁺/Er³⁺were 10%and 4%,the sample has the highest luminous intensity and emits orange-red light.?3?The Fe₃O₄ Nanoparticles were prepared by solvothermal method,Fe₃O₄@mSi O₂waspreparedbytemplatemethod,andFe₃O₄@mSiO₂@NaYF₄:Yb³⁺/Er³⁺nanocomposites were prepared by pyrolysis.The effects of reaction time,reaction temperature,solvent composition,and the doping concentrations were studied on the product of the conversion luminescence properties.The experimental results show that when the reaction temperature is 160?and the reaction time is 12 h,the Fe₃O₄ nanoparticles are the best.Fe₃O₄@mSiO₂@NaYF₄:Yb³⁺/Er³⁺has good luminescent properties when prepared at the temperature of 300?in the oleylamine by pyrolysis.