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

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.