Improvement of the red emission of Ag+/Mn2+co-doped NaMg(PO3)3 crystallized phosphors for possible application in UV-LEDs

NaMg(PO3)3 phosphates co-doped with Mn2+/Ag+ were prepared using the solid-state method at a temperature of 600 degrees 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.