Re The Cepo <sub> 4 </ Sub> Nano-fluorescent Material Preparation And Characterization

Luminescent nanomaterials of rare-earth phosphate with size-dependent optical and electronic properties have applications in many fields, such as data storage, photoelectronic devices, agriculture, military affair, and so on. In this thesis, luminescent nanomaterials of rare-earth phosphate have been successfully synthesized by using hydrothermal synthesizing method, and sonochemical synthesizing method. The crystal structures, dimensions, morphologies, compositions and purities were characterized with the techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), etc.The spectroscopic properties of the luminescent nanomaterials were investigated by photoluminescence spectroscopy. The luminescent mechanism of the CePO₄ and CePO₄:Tb nanomaterials is elucidated from point of view of the microstucture. The effects of doping of rare-earth metal ions, shell-core structure, the morphology, and the crystal structure on the fluorescent properties of rate-earth phosphates are extensively discussed. The main results are summarized as follows:1. A fluorescence nanomaterial of CePO₄ with different crystal structures and morphologies was hydrothermally synthesized.The effects of pH and the preparation temperature on the crystal structure, morphology and fluorescent intensity of CePO₄ were investigated. The results of SEM indicated that CePO₄ prepared in the acidic solution (pH 1, 120℃) has the morphology of nanorods, while CePO₄ prepared in alkaline solution (pH 12, 120℃) has the morphology of nanoparticles. The XRD results showed that CePO₄ prepared in acidic and alkaline (120℃) solution has a hexagonal crystal structure. However, the crystallinity of CePO₄ obtained in acidic solution is better than that obtained in alkaline solution. The crystal structure of CePO₄ depends on the preparation temperature. Fluorescence spectra indicated that both hexagonal and monoclinic CePO₄ showed a broad emission band between 300～450 nm due to the 5d-4f emission of cerium. However, the fluorescence intensity for the monoclinic CePO₄ is stronger than that of hexagonal one.2. CePO₄ crystal samples were synthesized and the effects of the preparation temperature on crystal structure of CePO₄ were studied. It was found that the CePO₄ with monoclinic structure can be growed on the surface of hexagonal CePO₄. These structures of CePO₄ were verified by XRD analysis.3. CePO₄:Tb nanomaterials were prepared by using ultrasonic method in inorganic salt aqueous solution. The effects of solution pH, ultrasonic irradiation time, and ultrasonic radiation strength on the crystal structure, morphology and fluorescent intensity of CePO₄:Tb were investigated. The results indicated that the acidic solution was favorable for 1D nanomaterials growth, which is similar to the provious reports. Fluorescence spectra indicated that the fluorescent properties of CePO₄:Tb were effected by the crystal structure, which is dependent on the ultrasonic time.