| In recent years, researches on luminescence materials have been concentrated onenergy applications rather than energy-efficient lighting solid materials driven byintensified evolution of shortage of natural resources, energy crisis, andenvironmental pollution etc., and the upcoming nanometer era. Rare-earth micro-andnanoscale materials have received extensive attention due to their unusual propertiesand potential applications in integrated optic system, high resolution displays,biological labeling, medical diagnosis, etc. At the same time, the study of dopedluminescence of rare earth ions system (including two aspects of theory andexperiment) also has more extensive, and the research on energy transfer process isstill need further research deeply.In inorganic micro/nano-materials, many factors have significant effects on thechemical and physical properties of the particals, the synthesis of inorganicmicro/nano-materials with morphology，special size and luminescent properties hasbeen significant. In a large of synthesis process, the hydrothermal method as thebriefest and environmental-protection synthetic way, which can be better controlledthrough appropriate choice of reaction parameters, such as temperature, pH and timeexpecting the substrate with ideal structure and the morphology through controllingthe experimental conditions flexibly. Based on the advantages of the hydrothermalmethod, we have successfully synthesis different phosphate by using the sodiumcitrate as the “shape modifiers”. The structure characteristics of the final productswere examined by several testing instruments,including powder X-ray diffraction(XRD), field emission-scanning electron microscopy (FE-SEM), transmissionelectron microscopy (TEM), photoluminescence (PL), decay curves,photoluminescent excitation spectra (PLE), electron paramagnetic resonance (EPR)and FT-IR spectrometer. In this thesis, the properties of the host substrate, opticalproperties of micro/nano-materials and energy transfer between rare earth ions were systematically investigated. The main contents of the research as follows:(1)In the present work, Ca5(PO4)3F： Ce3+/Mn2+microcrystals have beensuccessfully prepared by hydrothermal method by sodium citrate as the crystalmodifier. By chemical bond theory, we analyzed the crystal structure of Ca5(PO4)3F.The emission of Ce3+was fitted by two Gaussian functions to confirm the Ce3+ionsimultaneously occupy the4f and6h sites in Ca5(PO4)3F host. Results show that theposition of the center of Ce3+(6h) to the emission band (384nm) and the energy band(366nm) to Ce3+(4f). Experimental results show that, the existence of Ce3+(sensitizer)can dramatically enhance green emission of Mn2+(activator) in Ce3+/Mn2+ionsco-doped samples due to an efficient energy transfer from Ce3+to Mn2+.（2）Uniform and well-crystallized YPO40.8H2O and YPO40.8H2O:Tb3+, Eu3+nanocrystals have been successfully synthesized by a facile hydrothermal methodusing trisodium citrate (Cit3-) as the “shape modifier”. It was found that the pH valuein the initial solution was responsible for shape determination of final products, whenthe pH=6, uniform and well-crystallized hexagonal nanorods have been synthesizedwith a diameter of120nm and130nm length. In addition, the YPO40.8H2Osamples prepared by Cit3--assisted hydrothermal synthesis exhibited an intense andbright blue emission. Characterized with Fourier transform infrared (FT-IR) spectraand Electron paramagnetic resonance (EPR) spectra, paramagnetic defects relating tothe luminescence property existed in the luminescent YPO40.8H2O nanocrystals.More interesting was that the YPO40.8H2O:Tb3+, Eu3+samples could be effectivelyexcited with380nm and the luminescence colors of YPO40.8H2O: Tb3+, Eu3+nanocrystals can be easily tuned by changing the concentration of Eu3+ions due to anefficient energy transfer from Tb3+to Eu3+. These results revealed that thecombination of the defect luminescence and rare earth-doping emission in YPO40.8H2O: Tb3+, Eu3+nanocrystals could emit white color. |
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