Morphological and Phase Controlled Tungsten Based Nanoparticles: Synthesis and Characterization of Scheelite, Wolframite, and Oxide Nanomaterials

For the first time tungsten based nanoparticles (WNPs) of scheelite (MWO4: M = Ca, Sr, Ba, Pb), wolframite (MWO4: M = Mn, Fe; Zn and (Mg0.60Mn0.17Fe0.26)WO4), and the oxide (WO3 and W18O49) were synthesized from solution precipitation (i.e., trioctylamine or oleic acid) and solvothermal (i.e., benzyl alcohol) routes. The resultant WNPs were prepared directly from tungsten(VI) ethoxide (W(OCH2CH3)(6), 1) and stoichiometeric mixtures of the following precursors: [Ca(N(SiMe3)(2))(2)](2) (2), Pb(N(SiMe3)(2))(2) (3), Mn[(mu-Mes)(2)Mn(MeS)](2) (4), [Fe(mu-Mes)(Mes)](2) (5), Fe(CO)(5) (6), [Ba-2(mu(3)-ONep) (mu-ONeP)(2)(ONep)(HONeP)(3)(py)](2) (7), Sr-5(mu(4)-O)(mu(3)-ONeP)(4)(mu-ONep)(4)(HONep)(py)(4) (8), and [Zn(Et)-(ONep)(py)](2) (9) where Mes = C6H2(CH3)(3)-2,4,6, ONep = OCH2C(CH3)(3), Et = CH2CH3, and py = pyridine. Through these routes, the WNP morphologies were found to be manipulated by the processing conditions, while precursor selection influenced the final phase observed. For the solution precipitation route, 1 yielded (5 x 100 nm) W18O49 rods while stoichiometric reactions between 1 and 2-9 generated homogeneous sub-30 nm nanodots, -diamonds, -rods, and -wires for the MWO4 systems. For the solvothermal route, 1 was found to produce wires of WO3 with aspect ratios of 20 while (1 and 2) formed 10-60 nm CaWO4 nanodots. Room temperature photoluminescent (PL) emission properties of select WNPs were also examined with fluorescence spectroscopy (lambda(ex) = 320 nm). Broad PL emissions = 430, 420,395, 420 nm were noted for 5 x 100 nm W18O49 rods, 5 x 15 nm, CaWO4 rods, 10-30 nm CaWO4 dots, and 10 nm BaWO4 diamonds, respectively.