Hydrothermal Preparation Of Rare Earth Doped NaGd_xYb_1-xF₄ Monodisperse Nanocrystals And Their Luminescent Properties

In recent years,nanomaterials doped with lanthanide ions(Re³⁺)have received increasing attention in various fields owing to their wide applications in light emitting diodes,solar cells,lasers,biological analysis,biomedical and catalysts.Na Re F₄（Re=Y,Gd and Lu）nanocrystals with Re³⁺doped by hydrothermal preparation,which can achieve efficient up-conversion and down-conversion luminescence because of their low phonon energy related to crystal lattice and can also be dispersed in related solvents,have become attractive alternative materials for optical applications.Judd-Ofelt（J-O）theory fits three strength parametersΩ_λ（λ=2,4,6）through spectra.Important information with practical significance such as oscillator strength,probability of spontaneous radiation,fluorescence branching ratio,radiation lifetime and quantum yield can be easily obtained.However,the opacity of rare earth nanomaterials restricts the calculation of transition spontaneous emission,Na Re F₄（Re=Y,Gd and Lu）nanocrystals can be monodispersed in solvent and can maintain its transparency,this makes it possible to study its J-O parameters.In this paper,Er/Eu doped NaGd_xYb_1-xF₄ is used as the main research material.And the morphology,size and luminescence properties of monodisperse nanocrystals are investigated by adjusting the doping ratio.J-O theory is used to analyze and calculate the photophysical process of samples with different doping ratios.The main contents are as follows:1.A series of monodisperse nanocrystals of NaGd_1-x-yYb_yF₄:Eu_x（x=10%～50%,y=10%）were prepared by hydrothermal method.Combined with X-Ray Diffraction and Transmission Electron Microscope,the morphology was hexagonal nanorod-like,and the size is between 20nm～30nm.They have good monodispersity and can be dispersed in cyclohexane.The solution is clear and uniform,without delamination when standing.The ultraviolet light can be converted into red light.They are ideal monodisperse nanocrystals.2.Using Judd-Ofelt theory combined with the fluorescence spectrum of NaGd_1-x-yYb_yF₄:Eu_x（x=10%～50%,y=10%）samples,the J-O parameters of Eu³⁺ions under different doping ratios were fitted.As the doping concentration increases,the J-O parameter remains essentially the same;the ~5D₀ level luminescence under Eu³⁺still has a high quantum efficiency under heavy doping.3.A series of monodisperse nanocrystals of NaGd_1-x-yYb_yF₄:Er/Eu were prepared by hydrothermal method,and the relationship between monodispersity and nanocrystal size is explored.All the obtained nanocrystals with diameters of 40nm～440nm can be dissolved in cyclohexane and emit light stably.The transition from green light to yellow light to orange-red can be achieved by adjusting the concentration of Yb³⁺ions.4.Using Judd-Ofelt theory combined with the fluorescence spectrum and absorption spectrum intensity analysis of NaGd_1-x-yYb_yF₄:Er/Eu samples,the J-O parameters of Er³⁺ions under different doping ratios were obtained,and the concentration of rare earth ions dissolved in cyclohexane solution was calculated valid value.And the effective value of the concentration of rare earth ions dissolved in cyclohexane solution is calculated.5.Based on the good monodispersity of the sample,a composite of NaGd_xYb_1-xF₄:Er nanocrystals monodispersed in organic polymer materials was prepared.First,the synthesis of Polystyrene/NaGd_xYb_1-xF₄:Er is realized,the obtained nanocomposite has both transparent and luminescent properties.Secondly,the composite of epoxy resin/NaGd_xYb_1-xF₄:Er is carried out,a transparent composite material with fast synthesis process and high thermal stability was obtained.