Morphology-Controlled Synthesis, Physical Characterization, and Photoluminescence of Novel Self-Assembled Pomponlike White Light Phosphor: Eu3+-Doped Sodium Gadolinium Tungstate

Abstract

Three-dimensional pomponlike europium-doped sodium gadolinium tungstate NaGdWO4(OH)x:Eu3+ microarchitectures that exhibit efficient white-light photoluminescence properties have been successfully synthesized via a facile hydrothermal process in the presence of the surfactants cetyl trimethyl ammonium bromide, poly(vinyl pyrrolidone), and poly(ethylene glycol)-block-poly(propylene glycol)-block-ploy(ethylene glycol). The white light sodium gadolinium tungstate phosphor contains three emission bands: the blue-green band at 468 nm is ascribed to the ligand to metal charge transfer transition from O→W; the orange band at 590 nm and red band at 610 nm are attributed to the 5D0→7F1 and 5D0→7F2 transitions of Eu3+. The luminescence color can be tuned from blue to white to red by adjusting the doping concentration of Eu3+. Both scanning electron and transmission electron microscopy indicate that the obtained microspheres have a uniform particle size distribution. The three-dimensional sodium gadolium tungstate pompon-shaped structures were constructed layer-by-layer from a large number of two-dimensional nanoflakes with a mean diameter of ∼100 nm. The whole time-dependent process is interpreted as an example of self-assembly process. The emission spectra are dominated by a 5D0→7F2 transition of Eu3+. The optimum concentration for the white light was to keep the ratio of Eu3+ and Gd3+ at about 0.02.