Synthesis And Characterisation Of Rare-earth-doped Upconversion Luminous Materials

Three different rare-earth-doped upconversion luminous materials, Y2O3:Yb/Er, Na YF4:Yb/Er, Na Gd F4:Yb/Er, were synthesized through a solvothermal method in this paper. X-ray diffraction, scanning electron microscope, infrared spectroscopy, photo-luminescence spectra were used to characterize the synthesized samples. The optimum reaction conditions were determined based on the experiment. Comparing different doping concentration of rare earth ion, the photoluminescence performance was also studied. So it can be obtained upconversion luminous materials with controlled shape and better luminescence properties. The main results are as follows:Y2O3 micromaterials were synthesized via solvothermal method using YCl3 and CH3 COONa as precursors. To obtain the structure of microspheres, the optimal conditions to prepare good crystalline Y2O3 by hydrothermal are as follows: the reaction temperature is 180 °C, the reaction time is 20 h, the ratio of water and ethylene glycol(EG) is 3: 34 and the calcination temperature is 800 °C. The amount of EG played a key role on controlling the morphologies of the resulting products. Fluorescence analysis showed that the rare earth was doped in matrix materials successfully via solvothermal method. A optimum rare-earth doping amount was found in the experiment. The up-conversion fluorescence efficiency of Y2O3:Yb/Er powders is highest when the molar ratio of Y3+, Yb3+, Er3+ is 89: 10: 1.Upconversion microcrystals of Na YF4:Yb/Er were prepared through a one-step, simple, rapid, template-free and mild solvothermal synthesis method. Addition of Na2HPO4 influenced crystal transition from the cubic phase to the hexagonal phase in this experiment. Hexagonal-phase Na YF4:Yb/Er can be obtained at 200 °C for 3 h by simply controlling the amount of additives in the reaction system. Investigating the effects of addition of Na2HPO4 on the crystal transition process is a worthwhile endeavour that can reduce experiment costs and save a considerable amount of time. The p H of the solution had a significant effect on the morphology as well as the crystal phase of the prepared samples, resulting in the luminescence properties. When the p H is 2, the sample has best luminescence properties. The photoluminescence properties were studied and learned that, emission spectra of rare-earth doped samples exhibit characteristic peaks of Yb3+-Er3+ and have strongest emission peak centered at 542 nm and all of the samples show green emission. The best molar ratio of Y3+, Yb3+, Er3+ is 78: 20: 2.Na Gd F4:Yb/Er were selectively synthesized via hydrothermal method. The influence of reaction temperature, reaction time, p H of the solution, amount of EDTA and rare-earth doping on the structure, morphology and luminescence properties was investigated. XRD results indicated that Na Gd F4:Yb3+, Er3+ has a significant hexagonal phase, and the average grain size is about 31 nm. FT-IR testing shows that the samples contain hydroxyl groups, so they should have some hydrophilic property. Addition of EDTA could minish the size of particles and improve the dispersibility, although it will reduce luminescence properties.SEM shows that the samples present as irregular spheres with sizes of 50 nm when 0.5 g of EDTA is added.