Hydrothermal Controlled-synthesis And Luminescent Of Two Dimensions Rare-earth Fluoride Micro-/nano Materials

Rare earth fluoride luminescence nanomaterials with rich4f levels, show the characteristic of low phonon energy and the translucent range from the near ultraviolet to the infrared band. Rare earth fluoride nanomaterials have received widespread attention due to their unique optical, electrical, magnetic and other properties. In order to prepare the high performance rare earth fluoride nanophosphors, people have tried many different synthesis methods such as the precursor thermal decomposition method, hydrothermal/solvothermal method, polyol method, ultrasonic method, ionic liquid-assisted method and so on. Currently, morphology controlled synthesis of rare earth fluorides are mainly focus on the zero-dimensional (OD), one-dimensional (1D) or three-dimensional (3D). Compare to that of other dimensions, two-dimensional (2D) rare earth fluoride micro-nanomaterials received less attention due to the relatively difficulties for the preparation of the two-dimensional rare earth fluoride nanomaterials and the tendence to form3D structure during the process of crystal growth. The strong quantum confinement effect and boundary effects of the two-dimensional nanomaterials can effectively influence its performance. In addition, the larger surface-volume ratio of two-dimensional nanomaterials can improve the absorption effectively of PL excitation energy. So two dimensional nanomaterials have higher luminous efficiency. The controlled synthesis and optical properties of two-dimensional rare earth fluoride nanomaterials has important significance whether it is to improve the basic theory or to promote the implementation of the application.In this paper, two-dimensional luminescent nanomaterials (hexagon discoid NaDyF4, NaErF4, flakes NdF3,NaNdF4and perforated flake SmF3) have been prepared by mild hydrothermal method. The structure and morphology of products have been characterized by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Transmission electron microscopy (TEM). Growth behavior of two-dimensional rare earth fluoride micro-nanocrystalline and its possible mechanism has been proposed. Their optical properties have been analyzed through steady-state fluorescence spectrometer and the luminescence mechanism of rare earth fluoride under2D conditions has been proposed. The details are summarized as follows:1. Synthesis and characterization of binary flaky rare earth fluoride. Two-dimensional luminescent nanomaterials (flakes-like NdF3, NaNdF4and perforated SmF3flake) have been prepared using EDTA as morphology control agent under mild hydrothermal condition. the results shows that EDTA has played a crucial role on the formation of two-dimensional nanomaterials. EDTA can remarkable slow down the rate of nucleation and particle aggregation, simultaneously. The different adsorption capacity with different crystal plane lead to the products growing along two-dimensional direction ultimately. We studied the influence conditions on the morphology of the two-dimensional products and proposed growth mechanism of the two-dimensional rare earth fluoride nanocrystals.2. Synthesis and characterization of ternary flaky rare earth fluoride. Two dimensional rare earth fluoride NaLnF4(Ln=Nd, Er, Dy) were prepared successfully through hydrothermal method by changing experimental conditions (such as the initial concentration ratio, pH, reaction time, chelating agent species). The morphology of products are uniform, smooth surface and good dispersion. Formation mechanism and luminescent properties of products have been deeply studied.3. Studied the luminescent properties of the products. The results show that two-dimensional rare earth fluorides have excellent luminescent properties. NdF3and NaNdF4nanoflakes emission relatively strong infrared light with the same peak position in the infrared region under the excitation of394nm, suitable to be used for solid-state lasers. NaDyF4have two peaks in fluorescence spectrum corresponds to the4F9/2â†'6H15/2(blue) and4F9/2â†'6H i3/2(yellow). Due to yellow emission peak is stronger that the overall luminescence looks some bluish. The strongest luminescence of Sm3+is at594nm in the yellow region under the excitation of399nm, and there are important application value in the field of display and lighting. The luminescence of hexagon discoid NaErF4were characterized at room temperature. Luminescence mechanism of Er3+was analyzed and we found that luminescence of hexagon discoid NaErF4is stronger than that of hexagonal prism.