BaWO4:Eu phosphors were prepared by performing a solvothermal reaction in a water-hexane bilayer system. A barium oleate (and europium oleate) complex was obtained in hexane via a phase transfer reaction involving Ba2+ (and Eu3+) ions in an aqueous solution of sodium oleate. The outer surfaces of the nanometer-sized BaWO4:Eu phosphors were capped by the long alkyl chain of oleate; therefore, the hydrophobic nanorneter-sized BaWO4:Eu phosphors preferentially dissolved in the hexane layer. The micrometer-sized BaWO4:Eu phosphors were obtained in the water layer. The BaWO4:Eu phosphors prepared in hexane and water yielded sharp strong absorption and emission peaks at 464 and 615 nm, respectively, due to the E-7(0) -> D-5(2) and the D-5(0) -> F-7(2) transitions of the Eu3+ ions. The BaWO4:Eu phosphors are good candidate red-emitting phosphors for use in InGaN blue-emitting diodes, which have an emission wavelength of 465 nm. (C) 2016 Elsevier Ltd. All rights reserved.