Hydrothermal Controllable Synthesis And Mechanism Study Of Rare Earth Doped Up-conversion NaYF₄:Yb³⁺/Er³⁺ Materials

Rare earth doped up-conversion materials have attracted much attention in many applications of military,aerospace and biological areas because of their unique up-conversion luminescence behavior.At present,the preparation methods of high quality rare earth doped up-conversion materials mainly have cumbersome operations and low production.Therefore,exploring a simple and effective method for preparing high-quality rare earth doped up-conversion materials has practical application value for the up-conversion materials.The research of this thesis consists of three parts.First,the micron-grade NaYF₄:Yb³⁺/Er³⁺prepared by hydrothermal method which use diethylamine oxalate or sodium citrate as complexing agent was studied.Factors such as hydrothermal reaction temperature,surfactant type and dosage are also systematically investigated.The hydrothermal growth model of high-quality micron-grade rare earth doped up-conversion NaYF₄:Yb³⁺/Er³⁺materials is proposed.The hydrothermal growth of micron-level NaYF₄:Yb³⁺/Er³⁺is divided into four processes:1.Nucleation stage;2.Aggregation and fusion stage;3.Vertical growth stage;4.Ostwald ripening stage.A hydrothermal synthesis method for preparing nano-grade rare earth doped up-conversion NaYF₄:Yb³⁺/Er³⁺materials using citric acid as a complexing agent is proposed.The average particle size of the synthesized product is about?37.1 nm,and factors such as p H value of the solution,the heating rate were optimized.The study found that the ratio of Na⁺to Re³⁺will significantly affect the growth process of NaYF₄:Yb³⁺/Er³⁺,and a lower amount of Na⁺will not result in a hexagonal phase product with high luminous intensity.When the p H is low,the desired product can't be synthesized,and the product will have large micron-sized grains when the p H is high.Only when the heating rate is 1^oC/min,the nano-level homogeneous and pure phase products can be obtained.Introducing alkali metal K⁺and Li⁺ions into the hydrothermal system is studied.The K⁺ion induction was successful to achieve the preparation of nano-scale hexagonal phase up-conversion NaYF₄:Yb³⁺/Er³⁺materials,the average particle size is about?5.1 nm.The addition of Li⁺can successfully enter the NaYF₄:Yb³⁺/Er³⁺crystal by gap doping.When Na⁺in the hydrothermal system is replaced with three ions of Li⁺:Na⁺:K⁺=35:30:35,a special mixed-phase up-conversion material which has unique upconversion behavior can be obtained,with Li YF₄ and the cubic phase NaYF₄:Yb³⁺/Er³⁺as the main phase,and the hexagon phase NaYF₄:Yb³⁺/Er³⁺as the trace phase.