Nd-doped NASICON-type nanophosphors for near-infrared excitation and emission

Neodymium-doped phosphates, (Nd1-xGdx)0.33Zr2(PO4)3 (0 ≤ x ≤ 1), were synthesized by co-precipitation. (Nd1-xGdx)0.33Zr2(PO4)3 was obtained as a single-phase and was confirmed to be a NASICON-type structure consisting of a three-dimensional network of PO4 tetrahedra sharing corners with ZrO6 octahedra. The particle size of the (Nd1-xGdx)0.33Zr2(PO4)3 samples was in the nanoscale, which is suitable for in vivo optical imaging. The (Nd1-xGdx)0.33Zr2(PO4)3 samples showed characteristic luminescence corresponding to the f – f transitions of Nd3+. The highest emission intensity at 1072 nm with excitation at 824 nm was observed for (Nd0.75Gd0.25)0.33Zr2(PO4)3, which was 4.5 times higher than that of Nd0.33Zr2(PO4)3. The near-infrared (NIR) emission intensity of this nanophosphor was significantly higher than that of indocyanine green, which is actually used as an in vivo optical probe reagent.