Ultrafine Rare Earth Phosphate Nano-fluorescent Material Synthesis, Characterization And Performance Study

In this dissertation, nanospheres and nanorods of LaPO4, LnPO4 (Ln denotes Yb, Er, Dy, Tb, Gd, Sm, Ce or Y) nanocrystals, LnPO4:Eu and YPO4:(Eu3+, Li+) have been synthesized, respectively, of which optical properties have been investigated, accordingly. The details are presented as follows.Firstly, nanospheres and nanorods of LaPO4 have been synthesized by a hydrothermal method and a sol-gel method with La2O3 and NH4H2PO4as starting materials, respectively. TG-DSC,XRD,TEM as well as SEM have been employed to characterize the as-prepared samples. The results show that the samples are well dispersed and monoclinic monazite structure. The morphologies of the samples depend on the pH values of aqueous solution. At the low pH values, nanorod and nanowire morphologies tend to appear, and in the high pH, spherical morphology emerges. Meanwhile, the mechanism for the morphology transformation was proposed. Furthermore, the properties of the as-received samples with different morphologies were investigated. The results indicate that the spherical samples show the strongest emission intensity, the samples with rod and wire morphologies second, and the irregular aggregates samples the wrost.Secondly, a series of rare earth phosphates, LnPO4 (Ln denotes La, Y, Ce, Sm, Gd, Tb, Dy, Er, or Yb), with mean diameter of ca 100 nm have been successfully synthesized via a simple hydrothermal route. The procedure involves the formation of homogeneous and transparent metal-citrate-EDTA gel precursors using both citric acid (CA) and ethylenediamine tetraacetic acid (EDTA) as the complexing agents, followed by hydrothermal mineralization to yield the final LnPO4 nanocrystallites. XRD, TEM, and SEM have been employed to characterize the as-synthesized LnPO4 nanocrystals. The results show that the samples are well crystallized with hexagonal structure and in spherical morphologies with average particle sizes of around 20 nm. Furthermore, photoluminescence (PL) characterization of the Eu3+-doped LnPO4 nanocrystals was carried out. The results exhibit that the emission intensity of the as-prepared samples decreases with increasing the atomic number of lanthanide. The PL intensity and the symmetry ratios of the samples increase firstly and then decrease with the increase of the contents of Eu3+ in the compounds. The highest emission intensity was observed with the formula of LnPO4:5%Eu. Moreover, the pH value and reaction temperature have direct ratio relationships with the fluorescence intensity and the symmetry ratio.Finally, YPO4 nanoparticles with pure monoclinic phase were successfully synthesized by a simple sol-gel method using CA and EDTA as the complexing agents. The as-synthesized nanoparticles were characterized by means of XRD, TEM, SEM as well as HRTEM. Furthermore, the PL characterization of the Li+ and Eu3+ co-doped YPO4 nanocrystals was performed and the effects of the doping concentration of Li+ and Eu3+ active center concentration as well as calcination temperature on the PL properties have been studied in details. The results show that the incorporation of Li+ ions into the YPO4:Eu3+ lattice could induce a remarkable improvement of the PL intensity. The highest emission intensity was observed with 5% Li+ and 5% Eu3+ co-doped YPO4, whose brightness was increased by a factor of more than 2.5 in comparison with that of the YPO4:5%Eu.