Controlled Synthesis And Luminescent Properties Of 2D Rare Earth Fluoride Micro/Nano Crystal

Rare earth fluorides micro/nanomaterial with unique optical, electrical and magnetic properties, is a typical kind of luminescent materials. Because of its unique 4f level, low phonon energy, transmission range extends from near UV to the mid-infrared, rare earth fluorides micro/nanomaterials has a wide application in biological imaging, color display, optical detection, optical devices and solar cells. The controlled synthesis of rare earth fluoride micro/nanomaterials has become an important issue. Recently, Inspired by graphene, a typical kind of two-dimensional material, the controlled synthesis of other 2D inorganic nanomaterials such as metal chalcogenide, BN, transition metal oxides has moved into focus due to their unique 2D arthitecture and more excellent physical properties than that of the bulk material. Moreover, 2-D micro/nanomaterial is more easily prepared into film than orther nanomaterial (OD, 1D) and has potential application in electronic device, photosensitive transistor, energy storage and other fields.In this thesis, we successfully synthesized a series of 2D rare earth fluoride luminescent nanocrystals under mild conditions via hydrothermal method by reasonable choice of the initial ion molar ratio, pH value, reaction time and chelating agent. The structure, shape, size and luminescent properties have been characterized by X-ray powder diffraction, Field emission scanning electron microscope, Transmission electron microscopy and steady-state/lifetime fluorescence spectrometer, and then presented the possible formation mechanisms.The main contents of this paper are summarized as follows:1. A series of 2D rare earth fluoride nanocrystals (NaYF4, NaEuF4, NaSmF4, NdF3 nanosheets) have been synthesized by using oxalic acid as a chelating agent under mild hydrothermal conditions, The effect of some key reaction parameter such as initial ion molar ratio, pH, reaction time and chelating factors on the Morphology and structure has been studied.2. The morphology, structure and phase of the synthesized samples were characterized by XRD, TEM, SEM, HRTEM and ED techniques. The effects of various reaction conditions on the crystal morphology, structure and phase have been discussed, and the possible formation mechanism of 2D sheets has been proposed. Take NaYF4 microsheet for example, with increasing the reaction time, the NaYF4 crystal evolves from the cubic phase to the hexagonal phase, accompanied by thetremendous changes of the crystal morphology. Also the effect of the initial solution, the molar ratio of ions, pH and acid on the morphology, structure has been studied.3. The room temperature fluorescence spectra of synthesized samples have been investigated. The results show that different morphologies of Yb3+/Er3+co-doped NaYF4 fluorescence spectra exhibit quite different emission intensites yet with the same emission bands centered at 521nm,540nm and 654nm, which can be assigned to an electron transfer from the excited states 2H11/2,4S3/2 and 4F9/2 to the ground state 4I15/2, respectively. The luminescent intensity of NaYF4:Yb3+/Er3+ microsheet is stronger than microspheres. The fluorescence spectrum of Eu3+ doped NaYF4 sample has three distinct emission peaks and a relatively weak emission peaks, which correspond to a group of typical 5D0→FJ(J=1,2,3,4) transitions. The characterize emissions of Sm3+ are observed in the 560nm,593nm and 638un, which correspond to a group of typical 4G5/2→6HJ/2 (J=5,7,9,11) transitions in Sm3+doped NaYF4 microsheets. Meanwhile, the room temperature fluorescence spectra of NaEuF4, NaSmF4, NdF3 samples were also studied.