Role of manganese in red long-lasting phosphorescence of manganese-doped diopside for in vivo imaging

Abstract Materials with red long-lasting phosphorescence, such as Mn II -doped diopsides, can be used for small animal in vivo imaging. CaMgSi 2 O 6 :Mn powders with various amounts of Mn were prepared by sol–gel to investigate their long-lasting phosphorescence mechanism. X-ray diffraction, X-ray absorption fine and near-edge structure and electron paramagnetic resonance showed that manganese is quantitatively introduced in the structure as Mn II . Most of the Mn doping ions substitute Mg and possess a highly elongated octahedral environment. While photoluminescence and X-ray excited optical luminescence spectra show both orange (585 nm) and red (685 nm) 4 T 1 ( 4 G) → 6 A 1 ( 6 S) emission of Mn II Ca and Mn II Mg , respectively, Mn II Mg red emission dominates long-lasting phosphorescence and thermally stimulated luminescence spectra. These results point to Mn II Mg as the preferential hole trap and recombination center in the long-lasting phosphorescence mechanism. An intense persistent red emission suitable for in vivo imaging probes is obtained for the highest nominal Mn content (7.5%).