Highly Stable White Light Emission from III-Nitride Nanowire LEDs Utilizing Nanostructured Alumina-Doped Mn(4+) and Mg(2+)

[Image: see text] In this report, red-emitting alumina nanophosphors doped with Mn(4+) and Mg(2+) (Al(2)O(3):Mn(4+), Mg(2+)) are synthesized by a hydrothermal method using a Pluronic surfactant. The prepared samples are ceramic-sintered at various temperatures. X-ray diffraction shows that Al(2)O(3):Mn(4+), Mg(2+) annealed at 500 °C exhibits a cubic γ-Al(2)O(3) phase with the space group Fd3m-227. The tetragonal δ-Al(2)O(3) and rhombohedral α-Al(2)O(3) phase is obtained at 1000 and 1300 °C, respectively. Cube-like nanoparticles in a size of ∼40 nm are observed for the alumina heated at 500–1000 °C. The size and red-emitting intensity of the phosphors remarkably increased with annealed temperature ∼1300 °C. Emission spectra of the phosphors show strong peaks at 678 and 692 nm due to (2)E(g) → (4)A(2) transitions of the Mn(4+) ion, under a light excitation of 460 nm. A strong zero-phonon line (ZPL) emission is observed in the luminescence spectra of δ-Al(2)O(3):Mn(4+), Mg(2+) at 298 K, whereas a weak one is observed in those of α- and γ-Al(2)O(3):Mn(4+), Mg(2+). The alumina phosphors exhibited an excellent waterproof ability during 60 days in water and good thermal stability in the range of 77–573 K. A warm-white light-emitting diode (WLED) fabricated using In(x)Ga(1–x)N nanowire chips with Al(2)O(3):Mn(4+), Mg(2+) red-emitting nanophosphors presents a high color rendering index of ∼95.1 and a low correlated color temperature of ∼4998 K. Moreover, the current–voltage characteristic of the nanowire LEDs could be improved using Al(2)O(3):Mn(4+), Mg(2+) nanophosphors which is attributed to the increased heat dissipation in the nanowire LEDs.