Distribution Behavior And Luminescence Properties Of The Doped Rear-earth Ions In Up-conversion Materials

Rear Earth?RE?ions doped Up-conversion?UC?materials can convert photons of low energy to ones of high energy,and then present unique and excellent UC luminescence.However,there are still some problems in terms of low UC emission intensities and efficiency.Therefore exploring the existence and distribution behavior of doped RE ions in UC materials and understanding the network of energy transfer systems formed by sensitizer and activator ions within interior structures are vital for enhancing and optimizing the luminescent properties of UC materials.In this thesis,we analyzed the existence and distribution behaviors of RE ions in Indium composite oxide and NaYF₄ fluoride,and then developed a novel direct cation exchange of surface ligand capped upconversion nanocrystals to produce strong luminescence.The main results obtained are as follows:?1?Prepared rare earth ions(Yb³⁺/Er³⁺,Yb³⁺/Ho³⁺)doped SrIn₂O₄ and BaIn₂O₄composite oxide phosphors,and characterized their crystal structures and UC properties.In the structure,the doped RE ions always occupied the In³⁺sites because of similar ion radius and valance.The UC specra results demonstrate MIn₂O₄(M=Ca²⁺,Sr²⁺,Ba²⁺)are excellent UC matrix materials.?2?We employed synchrotron-based X-ray Photoelectron Spectroscopy?XPS?to characterize the depth distribution behaviors of Yb³⁺sensitizer ions in host NaYF₄nanoparticles.We find a radical gradient distribution of Yb³⁺from the core to the surface of the NaYF₄ nanoparticles,regardless of their size or sensitizer's concentration.A approximate inert shell comprised of Y³⁺ions on the surface was formed.This heterogeneous distribution pattern does favor the emission intensity of upconversion nanoparticles with high concentration of Yb³⁺sensitizer ions in the core region and less sensitizer ions on the surface to avoid the surface quenching effect.?3?We developed a novel direct cation exchange of surface ligand capped upconversion nanocrystals to produce strong luminescence.This method makes the cation exchange in NaGdF₄:Yb³⁺/Tm³⁺non-core-shell nanocrystals possible,and can easily render initial nanoparticles colorful UC luminescence.While the conventional cation exchange in water shows significantly quenched luminescence,the novel strategy can preserve 90.8%intensity of initial core-only nanocrystal template,and even generate 1.6-fold enhancement for the core-shell template under colloid state.This facile and rapid synthesis strategy opens a new gateway in the synthetic methodology for UCNCs.