The use of optically robust, luminescent lanthanide-based particles is becoming an area of interest for biolabel-related chemistry, due to their long lifetimes and range of non-overlapping absorption and emission lines from the visible to the near-infrared. We report the synthesis and optical properties of water-soluble, luminescent Ln(3+)-doped nanoparticles (NPs) coordinated with a hydrophilic (RO)PO32- ligand that facilitates the stabilization of the NPs in aqueous conditions, and that regulates particle growth to the nanometer range. The use of lanthanide ions as dopants, in particular Eu3+ and Er3+ ions, yields optically robust particles with narrow emission lines in the visible (591 nm) and in the near-infrared (1530 nm), respectively. Luminescent lifetimes range from the microsecond to the millisecond for Er3+ and Eu3+ ions, respectively, and the NPs are not expected to be susceptible to photo-bleaching due to the fact that the emissions arise from intra-4f transitions of the lanthanide ions.
