Improvement of the red emission of Ag⁺/Mn²⁺ co-doped NaMg(PO<inf>3</inf>)<inf>3</inf> crystallized phosphors for possible application in UV-LEDs

Abstract

NaMg(PO3)3 phosphates co-doped with Mn2+/Ag+ were prepared using the solid-state method at a temperature of 600 °C. X-ray diffraction analysis revealed the existence of a continuous solid solution during the substitution of Mg2+ by Mn2+ ions, confirmed by Vegard's law. Morphological studies reveal the presence of microcrystalline aggregates with sub-spherical crystal shapes displaying multiple growth steps reflecting the synthesis conditions and the shape of natural phosphates. The optical properties of samples were evaluated using UV–visible–Near InfraRed and photoluminescence spectroscopy. Four emission bands around 393, 418, 530, and 630 nm were observed and attributed to isolated Ag+ ions, Ag+-Ag0 pairs, Ag+-Ag+ pairs, and Mn2+ ions, respectively. An energy transfer mechanism is identified from the Ag + to Mn2+ and the red emission of Mn2+ was greatly enhanced under excitation at 255 nm of isolated Ag+ ions, which was confirmed by the luminescence spectra. These results indicate that NaMg(PO3)3 doped with 10 mol% Ag+ and 70 mol % Mn2+ could be a promising candidate for UV-LEDs emitting in the range between 200 and 300 nm.