Soft chemical synthesis and luminescent properties of Na3Al2Li3F12:Mn4+ garnet-type nanophosphor

Abstract For the first time we report the synthesis of nanocrystalline powders of Na3Al2Li3F12 phase, both pure and doped with Mn4+ using slow room temperature co-precipitation in methanol-water mixtures. Optical properties of obtained highly crystalline nanoparticles with the size in the range of 40–80 nm are studied. The synthesized Mn4+ doped fluoride garnet nanophosphors show typical Mn4+ luminescence spectrum in the red region (620–630 nm) under both photo- and 10 keV electron excitation, which is optimal emission wavelength for red phosphors in warm white LEDs. The relaxation dynamics of Mn4+ luminescence in this host has a complicated nature. Under the intra-centre excitation of Mn4+ ions and charge-transfer band excitation the decay is non-exponential in the studied temperature range, which indicates that there exists some additional mechanism of quenching, which is not related to intrinsic thermal quenching of Mn4+ luminescence.