Controlled Synthesis And Luminescence Properties Of Rare-Earth Lanthanum Phosphate Phosphors

Rod-like, spherical and core-shell structured rare-earth doped lanthanum phosphate phosphors were successfully synthesized through different synthesis methods. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectrometer (EDS), infrared spectroscopy (IR), x-ray photoelectron spectroscopy (XPS) and photo-luminescence (PL) spectra were used to characterize the synthesized samples. Effect factors on the morphology, phase structure and luminescence properties of the synthesized particles and the formation mechanism of different morphologies were discussed. The main results are as follows:(1) LaPO4:Ln3+ nanorods were selectively synthesized via a hydrothermal route, using La(NO3)3·6H2O and NaH2PO4 as raw materials. The influence of reactant molar ratio, reaction temperature and pH value on the structure, morphology and luminescence properties was investigated. The results were as follows. The LaPO4:Eu3+ nanorods with monoclinic phase structure had the maximum emission intensity when the reactant molar ratio was 1:4. With the increase of the reaction temperature, the length of the nanorods could be increased and the uniformity of the samples would be improved. The pH of the solution had a significant effect on the length as well as the dispersion of the prepared samples. With the increase of the pH vaule, the morphology of the sample was gradually changed from a single nanorod into nanoclusters assembled by nanorods. Fluorescence analysis showed that the best concentration of Eu3+is 5% for the nanorods. And other rare earth ions doped LaPO4 nanorods also had strong emission intensities, which illustrated that the LaPO4 nanorods were good matrix materials.(2) LaPO4:Ln3+ microspheres were selectively synthesized via hydrothermal method, using La(NO3)3-6H20 and H6P4O13 as raw materials. The influence of reactant molar ratio, reaction time and the amount of HNO3 on the structure, morphology and luminescence properties was investigated. The results were as follows. Monodisperse LaPO4 microspheres with the diameter of about 2 μm could be obtained when the reactant molar ratio was 1:7 or 1:8 and the reaction time was 6 h. The amount of HNO3 played a key role in controlling the morphologies of the resulting products. With the increase of the anmount of HNO3, the morphology of the samples changed from microspheres to particles. The relative emission intensity of Eu3+ reached a maximum when the amount of HNO3 was 3mL. And other rare earth ions doped LaPO4 microspheres also had strong emission intensities, which illustrated that the LaPO4 microspheres were good matrix materials.(3) SiO2@LaPO4:Eu3+ and MF (the melamine formaldehyde)@LaPO4:Eu3+ phosphors were prepared by wet chemical method, using SiO2 and MF as cores and La(NO3)3-6H2O and NaH2PO4 as raw materials of shell. The results were as follows. The amount of ammonia had an influence on the uniformity of SiO2. The amount of formic acid and the reaction time had a significant influence on the size of MF spheres. The amount of NaOH played an essential role in the formation of the SiO2@LaPO4 and MF@LaPO4. The emission intensity increased with the increase of the coating number. When the coating number was four, the emission intensity of core-shell phosphors could reach about 63.8% of that of pure LaPO4:Eu3+ powders, which illustrated that the SiO2@LaPO4 microspheres were good matrix materials. And this method can be applied in preparing other core-shell materials.