Solution-Phase Controllable Synthesis And Fluorescence Properties Of Several Lanthanum-Containing Compounds

It is very important to synthesize the rare-earth luminescence materials and optimize its optical properties during researching and developing new functional materials. Now lots of efforts have been paid to the solution-based synthesis and optical properties of lanthanum-containing compounds. Many researches reveal that the doped lanthanum fluorides possess many interesting and improved optical properties, which can be applied in many fields of plasma panel displays, field emission displays and solid state lasers. Owing to unique and excellent optical properties, the LaVO4based phosphors have been also applied in luminescence lighting (LLT), field emission display (FED), cathode ray tubes (CRTs), and plasma display panels (PDPs).In this dissertation, some improved hydrothermal methods were used to prepare lanthanum-containing phosphors, and the microstructures, morphologies and fluorescence properties of the as-synthsized phosphors were detailedly investigated. The main contents are as follows:(1) A simple hydrothermal method was applied to prepare LaF3:Eu3+red phosphors, and the as-prepared samples were characterized by XRD, TEM(HRTEM), SEM, UV-vis, Raman, IR and FL Spectrometry. The effects of reaction conditions such as pH, reaction time, reaction temperature, Eu3+content, fluorin source, sodium nitrate content, calcination time and temperature, and solvent etc. have been investigated.The resuls display that LaF3:Eu3+nanoparticles with a hexagonal structure are well crystallizable. The LaF3:Eu3+nanocrystals excitated at397nm (7F0â†'5L6) possess very strong orange-red emission (592nm,5D0â†'7F1) when the optimum doping concentration of Eu3+is determined to be10mol.%. The calcined samples take on good red emission (619nm,5D0â†'7F2) than that of the uncalcined samples. The Eu-doping concentration more than10%will result in fluorescence quenching.(2) Highly crystalline LaPO4：Eu3+nanorods were successfully synthesized by a facile ethanol-water solvothermal method. The obtained products were characterized by XRD, TEM, HRTEM and Fluorescence Spectrometry. The effects of pH values of the solutions, reaction time, reaction temperature, and the doped Eu3+concentration were investigated in detail. The obtained LaPO4:Eu3+nanorods change from30to200nm in length and vary in the range of20-25nm in diameter, which are agreement with the results from transmission electron microscopy (TEM). The rod-like LaPO4:Eu3+phosphors monitored at252nm exhibit very good orange-red emission (593nm). When the doped Eu3+concentration is5%, the fluorescence intensity of the La0.95Eu0.o5PO4is the strongest than others.(3) An environmentally friendly solvothermal process assisted by EDTA or glucose was designed to fabricate tetragonal (t-) phased LaVO4:Dy3+with three regular morphologies. The as-prepared products were characterized by XRD, TEM, SEM, XPS, FTIR, UV-vis and PL. The effects of pH, reaction temperature and reaction time, and surfactant (EDTA, glucose) on the crystal structure and morphologies of the samples were detailedly discussed, and LaVO4:Dy3+nanoparticles, nano/microrods and sphere-like structures were obtained via tailoring the conditions of reaction solution. Besides, the fluorescence characteristics of LaVO4:Dy3+crystals with novel morphologies were also investigated. The characterized results show that the emission intensities of rod-like LaVO4:Dy3+crystals will enhance with increasing the annealing temperatures. In Comparison with the samples with the shapes of micro-sphere and irrregular nanoparticles, rod-like LaVO4:Dy3+crystals exhibit the best fluorescence properties.