Synthesis And Luminescent Properties Of The NaErF₄,K₂ErF₅ Microcrystals

Since the 1990s,anti-Stokes luminescence nanoparticles,namely upconversion nanoparticles?UCNPs?,have been reported as a kind of new photoluminescent nanomaterials.In contrast with traditional Stokes photoluminescence?down conversion luminescence?,upconversion luminescence is the process of converting low energy photons into high energy emissions.These luminescence materials were widely concerned due to their unique photophysical properties,such as low background fluorescence interference,long luminescence lifetime,high light stability,and large anti-Stokes shift.Because of these unique advantages,upconversion luminescence materials have been widely used in biomedical fields such as biosensing,bioimaging and therapeutics.However,there are many energy losses during upconversion luminescence process.For example,the non-radiative relaxation process causes thermal vibration of the matrix lattice,which causes the temperature of the material to rise,resulting in low up-conversion luminescence efficiency,which hinders further application of the up-conversion luminescent material.Therefore,improving the luminescence efficiency of the up-conversion material is of great significance for practical applications.This thesis is focused on improving the luminescent efficiency of rare earth doped luminescent materials.The obtained main results are as follows:?1?NaErF₄ microcrystals with different morphologies were synthesized by a simple hydrothermal method.Yb³⁺-doped NaErF₄ microcrystals exhibited red and green upconversion?UC?luminescence excited by 980 nm and 1560 nm lasers,respectively.The luminous intensity in the green region showed stronger under 1560 nm excitation than that under 980 nm excitation.Moreover,the intensities of eye-visible red and green luminescence were increased after doping Fe³⁺ion.In addition,the doping of Fe³⁺ion endows NaErF₄ with magnetic characteristics,realizing the dual functions?optical and magnetic?.Furthermore,the doping of Fe³⁺ion maked the microcrystals structure easy to evolve.The effects of Fe³⁺ion doping concentration and the molar ratio of F:Ln on the microcrystals structure of NaErF₄:20%Yb³⁺were studied.Our work would afford a new doorway for designing the multifunctional materials with controllable double-color luminescence and optical-magnetic characteristics.?2?A series of Yb³⁺/Ho³⁺/Cr³⁺tridoped K₂ErF₅ microcrystals were synthesized by a facile solvothermal method for the first time.The morphology and upconversion luminescence of the K₂ErF₅ microcrystals were systematically studied.It was found that the red emission?654 nm?of K₂ErF₅ microcrystals was selectively enhanced by introducing Ho³⁺ion.In order to further improve red luminescence intensity,Cr³⁺ion was doped in K₂ErF₅microcrystals.The red luminescence intensity reached maximum value when Cr³⁺ion concentration was 7 mol%.The mechanisms of the luminescence enhancement were attributed to the synergistic effect among the energy transfer process,the improvement of the microcrystals'crystallinity and the distortion of the local crystal structure with lower symmetry when the Ho³⁺and Cr³⁺ions were introduced.