Controlled Synthesis And Luminescence Properties Of REF₃ Monodispersed Particles

In this dissertation,nano-sized rare earth fluorides have been synthesized by hydrothermal and solvothermal processing,and the phase,crystal structure,particle morphology,effect of ion doping and fluorescence properties have been investigated.The optimized synthesis conditions of precursors(NH4)Y3F10 and REF3 have been defined,along with the effects of citric acid and tartaric acid complexing agents on morphology,and the sensitizing effect and energy trnafer mechanism of Nd3+?Yb3+under 808 nm excitation.Detailed characterizations of the products were performed by the combined techniques of XRD,FT-IR,FE-SEM and PLE/PL analysis.The following conclusions have been reached:Cubic precursor(NH4)Y3F10:RE3+(RE=Yb3+/Er3+,Yb3+/Tm3+,Yb3+/Ho3+)has been successfully synthesized by hydrothermal and solvothermal method.The precursor decomposed into orthorhombic YF3:RE3+at a low-temperature calcination temperature of 400 and 500?,so the morphology control of YF3:RE3+was realized by adjusting the morphology of the precursor.The research shows that adding appropriate amount of complexing agent can change the growth mode of crystal grains,thus the final products present different morphology characteristics.The addition of citric acid in the reaction system was beneficial to the formation of flaky(NH4)Y3F10 particles.The morphology of the product was mostly regular hexagonal sheet(lateral size of?200-300 nm)at pH=5 and EG of 20 mL.The addition of tartaric acid in the reaction system was beneficial to the equiaxed spherical(NH4)Y3F10 particles.When the hydrothermal conditions are 120?,24 h,R(n(Tar2-):n(Ln3+))=0.3,spherical particles with uniform size(particle size?200 nm)can be obtained.After calcination at 400? and 500?,orthorhombic YF3:Yb3+/Tm3+and YF3:Yb3+/Ho3+ were obtained without obvious change in morphology,and the products were monodisperse fluorescent particles.Under the 980 nm infrared excitation,YF3:Yb3+/Er3+,YF3:Yb3+/Tm3+,YF3:Yb3+/Ho3+exhibited intense yellow emission(4S3/2?4I15/2 and 4I9/2?4I15/2 transition of Er3+),red emission(3F3/3F2?3H6 and 3H4?3H6 transition of Tm3+)and green emission(5S2/5F4?5I8 transition of Ho3+),respectively.Regular particle morphology can form close packing,which can reduce the scattering of excitation light and thus lead to the improvement of fluorescence intensity.Inncreasing the calcination temperature induced reduced surface defects of crystal grains,improved crystallinity and increased crystal grain size,which improve the up-conversion efficiency.Ellipsoid hexagonal(Y,Nd,Yb)F3 fluoride solid solution with particle size of?20-40 nm was prepared by solvothermal method.(Nd1-xYbx)F3 samples showed a linear decrease in lattice parameters with the increase of Yb3+ content,which conforms to Vegard's law.The grain size gradually decreases with the increase of Yb3+.Under 808 nm excitation,the nanoparticles exhibit characteristic emission peaks at 980 nm(2F5/2?2F7/2 transition of Yb3+),860 nm(4F3/2?4I9/2 transition of Nd3+)?890 nm(4F3/2?4I11/2 transition of Nd3+),1060 nm(4F3/2?4I13/2 transition of Nd3+)and 1330 nm(4F3/2?4I15/2 transition of Nd3+).When Yb content is 5%,the(Nd1-xYbx)F3 sample exhibits the strongest fluorescence emission.When Nd content is 60%,the(Y1-yNdy)F3:0.07Yb3+ sample exhibits the best fluorescence.