Silica-coated and uncoated, Tb-doped (1-5 at % Tb) Y(2)O(3) green nanophosphors were made, for the first time, in a single step by flame aerosol technology with controlled crystal phase (cubic and monoclinic) and morphology. The nanophosphors were characterized by X-ray diffraction, N(2) adsorption, high resolution electron microscopy, and photoluminescence spectroscopy. The monoclinic crystal structure of Y(2)O(3):Tb(3+) nanophosphors favors the electric dipole (5)D(4) → (7)F(5) transition driving their green phosphorescence. The phosphorescence of the SiO(2)-coated monoclinic Y(2)O(3):Tb(3+) nanophosphors is lower than the uncoated ones. Upon annealing these nanophosphors, they were transformed from monoclinic to cubic and their phosphorescence was reduced. This further indicates the superior performance of the monoclinic crystal phase for the electric dipole transitions of Tb(3+) ions.