Study on the Hydrothermal Synthesis and Fluorescence of LaF3∶Tb3+, Ce3+ Nanocrystals
XU Shi-hua1, HUANG Zhong-jing1*, LIU Guo-cong2*, WEI Qing-min3
1. College of Chemistry & Ecological Engineering, Guangxi University for Nationalities, Nanning 530008, China 2. Department of Chemical Engineering, Huizhou University, Huizhou 516007, China 3. Department of Chemistry, Yulin Normal University, Yulin 537000, China
Abstract：LaF3∶Tb3+, Ce3+ nanocrystals were prepared with hydrothermal method with the help of cetyltrimethyl ammonium bromide (CTAB). The effects of pH values of the solution, Ce3+/Tb3+ ratio value and reaction time on the luminescent properties were investigated. XRD analysis shows that the as-prepared samples possess hexagonal phase and their main diffraction peaks of samples are similar to the standard card (JCPDS 32-0483). Compared with pure LaF3, the main diffraction peaks of the doped samples have a slight shift, showing existing isomorphous substitution between La3+ and the doped rare earth ions in parent lattice of LaF3. It is found from TEM results that the as-prepared samples have good crystallinity and their average grain sizes change in the range of 20～50 nm. The excitation spectra indicate that the stronger excitation spectrum peaks exist at 250 nm, which is assigned to the transition of 4f→5d from Ce3+. When activated at 250 nm, all LaF3∶Tb3+, Ce3+ nanocrystals possess weak blue emission at 490 nm (electric dipole transition, 5D4→7F6) and good green emission at 543 nm (magnetic dipole transition, 5D4→7F5). As the Ce3+/Tb3+ ratio increases, the fluorescence intensities increase at first and then weaken, and reach the strongest green emission at nCe3+/nTb3+=4. The pH values have some influence on the colors and intensities of the LaF3∶Tb3+, Ce3+ nanocrystals. The sample prepared at pH 9 presents the best color, while the one at pH 7 exhibits the strongest green emission. Besides, increasing reaction time is helpful to improve color purity of sample and enhance its green emission.
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