Enhanced red emission of glycothermally synthesized Ce:YAG nanophosphors via Mn2+ addition

Mn2+ was shown to be incorporated as a co-dopant in glycothermally synthesized Ce:YAG-based nanophosphors to enhance the red component of the emission spectrum. Structural characterization showed a preferential inclusion of Mn2+ in the Y site. AlIV/AlVI ratios were found to decrease from 0.25 in Ce:YAG nanophosphors to 0.11 with the addition of Mn2+, indicating a ∼10x increase in octahedral Al sites over bulk Ce:YAG, particularly on the particle surface. Luminescence of Mn2+ at 594 nm, indicating octahedral Al site occupation was also observed, likely due to the high doping concentration of Mn2+. Strategies to improve the luminescence of Mn2+ included adding Si4+ in the form of tetraethyl orthosilicate (TEOS) for charge compensation and the addition of an intrinsic shell layer to enhance the local crystal field. XPS confirmed no change of Mn2+ valence after reaction, indicating Mn (II) acetate to be a precursor compatible with the glycothermal method for the synthesis of Ce:YAG-based nanophosphors. 3 mol% Mn2+ was found to be a suitable doping concentration, with quenching observed at 5%. Addition of an intrinsic shell layer greatly improved the optical characteristics of the Mn2+ emission, and the photoluminescence quantum yield (PLQY) increased from 44% to 73%. Fluorescence lifetimes of nanocrystalline Ce:YAG and Mn2+ containing samples dropped from 101.1 ns to 90.7 ns, respectively, indicating the presence of a non-radiative energy transfer mechanism from Ce to Mn2+.