Sensitization of near-infrared LnIII [Ln = Yb or Nd] ions using water-soluble, band gap tuneable 3-MPA-capped CdS nanoparticles

Abstract

We synthesized 3–4 nm crystalline, cubic phase, monodisperse 3-mercaptopropionato capped CdS nanoparticles (3-MPA-NPs) with different heating reaction times. Their aqueous fluorescence emission quantum yields were in the range 2.0–3.4%, with biexponential lifetimes in the range 34–50 ns (surface states) and 303–477 ns (core states), which increased linearly with increasing heating reaction time. The NPs were then decorated with near-infrared emitting Nd^III and Yb^III ions through chelation to the surface carboxylato groups of 3-mercaptopropionato (3-MPA-Ln-NPs). Excitation of these NPs at their maximum absorption wavelength resulted in emission of the surface-bound Ln^III ions with efficiencies in the range 0.01–0.02%. The overlap of the excitation spectra of the Ln^III-containing systems, 3-MPA-Ln-NPs, with the absorption spectra of the NPs indicates that energy was transferred from the NPs to the metal ions coordinated to the surface 3-MPA.