Synthesis And Characterization Of Rare-Earth Ions Doped Core-Shell Phosphors By The Pechini Sol-gol Process

Core-shell structured luminescent materials, including rare earth doped Y₂O₃ andYVO₄ were synthesized by Pechini sol-gel using monodisperse SiO₂ as cores. The luminescence of rare earth ions (Eu³⁺, Dy³⁺, Sm³⁺) and energy transfer properties from VO₄3-to Dy³⁺, Sm³⁺ were studied in core-shell structured luminescent materials.Core-shell structured SiO₂@Y₂O₃:Eu³⁺phosphor powders were obtained by coating mondisperse SiO₂ particles with Y₂O₃:Eu³⁺ phosphor layer through Pechini sol-gel method. The results of FESEM and TEM indicated that the core-shell structured phosphor particles were smooth and uniform, maintained the morphology of monodisperse SiO₂. The thickness of the shells could be easily controlled by changing the number of deposition cycles (60 nm for three deposition cycles). Under the excitation of ultraviolet (250 nm) and electron beams (1-6kV), the Eu³⁺ ion mainly shows its characteristic red (611nm, 5D0-7F2) emissions in the core-shell particles. The kinetic properties for the luminescence of Eu³⁺ in SiO₂@Y₂O₃: Eu³⁺ particles were investigated by PL decay and time-resolved emission spectra. The PL decay curves of for the luminescence of Eu³⁺ (5D1-7F1 and 5D0-7F2) in SiO₂@Y₂O₃: Eu³⁺ particles can be well fitted by a single exponential function as I(t)=I0exp(-t/Ï„), and the lifetimes for 5D0 ( detected at 611 nm), 5D1 (detected at 535 nm) of Eu³⁺ were determined to be 1637 and 40μs, respectively. We can better understand the relaxation process from 5D1 to 5D0 for the luminescence of Eu³⁺ by analyzing the time-resolved emission spectra. The cathodoluminescence (CL) spectrum of SiO₂@Y₂O₃:Eu³⁺ core-shell phosphors is similar to that of the PL emission spectrum. The CL intensity increases with increasing the filament current and the accelerating voltage and excellent dispersing properties of SiO₂@Y₂O₃:Eu³⁺ core-shell phosphors, they are potentially applied in field emission display devices.Spherical SiO₂ Particles have been coated with YVO₄: R³⁺ (Dy³⁺, Sm³⁺) phosphors layers by a Pechini sol-gel process. The resulted core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca.300 nm), smooth surface and non-agglomeration. The doped Dy³⁺, Sm³⁺ shows a strong photoluminescence (PL) due to an efficient energy transfer from YVO₄ host to them. The decay curves for emission 4F9/2– 6H13/2 (583nm) of Dy³⁺ and 4G5/2-6H7/2 of Sm³⁺ can be well fitted into a double exponential function as I = A1 exp (-t /Ï„1) + A2 exp(-t /Ï„2). Thus the average lifetimes of Dy³⁺ (4F9/2-6H13/2) and Sm³⁺ (4G5/2-6H7/2) emission can be determined to be 0.118 ms and 1.441 ms, respectively.The photoluminescence intensity of SiO₂@Y₂O₃:Eu³⁺ and SiO₂@YVO₄: Dy³⁺/Sm³⁺ core-shell phosphors can be tuned by several experimental factors, such as annealing temperature, PEG concentration in the precursor solution, the number of coatings and SiO₂ core sizes.