Highly Stable White Light Emission from III-Nitride Nanowire LEDs Utilizing Nanostructured Alumina-Doped Mn4+and Mg2+

In this report, red-emitting alumina nanophosphors doped with Mn4+ and Mg2+ (Al2O3:Mn4+, Mg2+) are synthesized by a hydrothermal method using a Pluronic surfactant. The prepared samples are ceramic-sintered at various temperatures. X-ray diffraction shows that Al2O3:Mn4+, Mg2+ annealed at 500 degrees C exhibits a cubic gamma-Al2O3 phase with the space group Fd3m-227. The tetragonal delta-Al2O3 and rhombohedral alpha-Al2O3 phase is obtained at 1000 and 1300 degrees C, respectively. Cube-like nanoparticles in a size of similar to 40 nm are observed for the alumina heated at 500-1000 degrees C. The size and red-emitting intensity of the phosphors remarkably increased with annealed temperature similar to 1300 degrees C. Emission spectra of the phosphors show strong peaks at 678 and 692 nm due to E-2(g) -> (4)A(2) transitions of the Mn4+ ion, under a light excitation of 460 nm. A strong zero-phonon line (ZPL) emission is observed in the luminescence spectra of delta-Al2O3:Mn4+, Mg2+ at 298 K, whereas a weak one is observed in those of alpha- and gamma-Al2O3:Mn4+, Mg2+. 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 InxGa(1-x)N nanowire chips with Al2O3:Mn4+, Mg2+ red-emitting nanophosphors presents a high color rendering index of similar to 95.1 and a low correlated color temperature of similar to 4998 K. Moreover, the current-voltage characteristic of the nanowire LEDs could be improved using Al2O3:Mn4+, Mg2+ nanophosphors which is attributed to the increased heat dissipation in the nanowire LEDs.

Automated summary

Red-emitting alumina nanophosphors doped with Mn4+ and Mg2+ (Al2O3:Mn4+, Mg2+) were synthesized using a hydrothermal method and Pluronic surfactant. The nanophosphors showed different phases depending on the annealed temperature, with cube-like nanoparticles observed at 500-1000°C. The phosphors exhibited strong red emission at 678 and 692 nm due to the transitions of Mn4+ ions, and displayed excellent waterproof ability and thermal stability. Combining the nanophosphors with InxGa(1-x)N nanowire chips, warm-white LEDs with high color rendering index and low correlated color temperature were achieved. The use of nanophosphors also improved the current-voltage characteristic of the LEDs.