Synthesis And Characterization Of Rare-Earth Ions Doped Nanostructured Phosphors By The Sonochemical Process

Nanostructured luminescent materials, including rare earth doped Ba₂GdNbO₆,LnVO₄ (Ln = La-Lu) and LnPO4(Ln = La-Ho) were synthesized by solid state methods and sonochemical methods respectively. Suitable amount incorporation of Li+ ions in the phosphors can promote the crystallinity and increase the grain size to a great extent, and thus enhance the PL emission intensity greatly. The luminescence of rare earth ions (Eu³⁺, Dy³⁺) and energy transfer properties from VO₄3- to Eu³⁺, Dy³⁺were studied in nanostructured luminescent materials.The Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li+-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors were prepared by solid-state reaction. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) as well as lifetimes was utilized to characterize the resulting phosphors. Under the excitation of ultraviolet light, the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li+-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ show the characteristic emissions of Eu³⁺ (5D0-7F1 transitions) and Dy³⁺ (4F9/2-6H15/2 transitions), respectively. The incorporation of Li+ ions in the phosphors can promote the crystallinity and increase the grain size to a great extent, and thus enhance the PL emission intensity greatly. The method might be used for other phosphors to enhance their emission intensity.The synthesis of the lanthanide orthovanadate LnVO₄ (Ln = La-Lu) and lanthanide orthophosphate LnPO4(Ln = La-Ho) nanoparticles using sonochemical method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) spectra as well as kinetic decays were applied for characterization of the as-prepared products. The ultrasonic irradiation has a strong effect on the morphology of the LnVO₄ and LnPO4 (Ln = La-Ho) nanoparticles. The SEM and TEM images illustrate that the as formed LnVO₄ particles have spindle-like shape with an equatorial diameter of 30-70 nm and a length of 100-200 nm, which are the aggregates of even smaller nanoparticles of 10-20 nm. The results of XRD confirm the formation of well crystallized LnVO₄ phase with the tetragonal zircon structure. Eu³⁺ and Dy³⁺ doped the zircon type LnVO₄ (Ln = La, Gd, Lu) samples show the characteristic dominant emissions of Eu³⁺ 5D0-7F2 at 613 nm and Dy³⁺ 4F9/2-6H13/2 at 572 nm, respectively. An energy level diagram was proposed to explain the luminescence processes in these nanophosphors. The possible formation mechanism of the spindle-like LnVO₄ nanoparticles with the application of ultrasonic irradiation was discussed in the context. The XRD patterns confirm that the (La-Gd)PO4 have a hexagonal structure and (Tb-Ho)PO4 crystallize in a tetragonal structure under the same synthetic conditions. SEM and TEM images show that (La-Gd)PO4 samples demonstrate that they have rod-like shapes. However, the (Tb-Ho)PO4 show the bundled nanowires morphology. Eu³⁺ andTb³⁺ doped LaPO4 and CePO4 show characteristic emission of Eu³⁺ (f-f) and Tb³⁺ (f-f), respectively. An efficient energy transfer from Ce³⁺ to Tb³⁺ in CePO4 host was discussed and the possible formation mechanism for these nanostructures is proposedThe morphology of nanostructured, the photoluminescence intensity of the Ba₂GdNbO₆: Eu³⁺/Dy³⁺, Li+-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺,LnVO₄:Eu³⁺/Dy³⁺(Ln = La, Gd, Lu) and LaPO4:Eu³⁺,CePO4:Tb³⁺, and the applications of the phosphors were discussed in this text.