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

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 Fd 3 m -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.
Competing Interests: The authors declare no competing financial interest.
(© 2023 The Authors. Published by American Chemical Society.)