The effect of surface-capping oleic acid on the optical properties of lanthanide-doped nanocrystals.

The rapid development of nanotechnology has placed a higher demand on the synthesis of nanomaterials. Benefiting from its capability to keep nanoparticles away from aggregation, oleic acid (OA) has been routinely utilized as a capping agent in the synthesis of monodisperse nanocrystals. To satisfy downstream biological applications, hydrophobic OA capping on the surface should be removed or coated, but scarce attention has been paid to its influence on the optical properties of nanocrystals. In this work, the effect of surface-capping OA has been systematically explored on the optical properties of lanthanide-doped upconversion and downshifting nanocrystals, respectively. The emission intensity and lifetime of emissive lanthanides have been compared between OA-capped and ligand-free nanocrystals either in solid state or in colloidal solution. In solid state, surface-capping OA can significantly influence both emission intensity and radiative transition possibility of emissive lanthanides. However, in colloidal solution, a distinct variation between OA-capped and ligand-free nanocrystals is observed. Besides, the effect of OA on the luminescence dynamics of lanthanides with different energy gaps (emitting level to the next-lower-energy level) has been investigated in colloidal solution. The possible mechanism for the effect of OA on the optical properties of lanthanide-doped nanocrystals has been further proposed.

Thinning shell thickness of CuInS2@ZnS quantum dots to boost detection sensitivity.

Quantum dots (QDs), drawing large attention during the past three decades, have been extensively applied in lighting, display, and biodetection. However, the mechanism for their ability in biodetection, especially in recognizing toxic metal ions, has scarcely been explored. In this work, three sets of CuInS2@ZnS QDs systems with inert shell thickness varying from 1.1 to 4.1 nm have been performed. As the shrinkage of inert shell, QDs not only show red-shift emission but also demonstrate more sensitive and higher response to the added Cd2+. The thin-shell CuInS2@ZnS QDs could detect 0.91 nM Cd2+, and could further detect 4.36 nM Cd2+ when integrated with paper-based platform. Importantly, thin-shell CuInS2@ZnS QDs combined with paper-based platform can detect 105.86 nM Cd2+ even just applying mobile phone as detector and hand-held UV lamp as excitation resource. The mechanism is further proposed based on the energy transfer routes. The thin inert shell can not completely protect the emissive core away from the surface defects, but it can neither exclude the energy transfer from the surface to the emissive core. The added Cd2+ would facilitate the formation of CdS on the surface of QDs, which not only can alleviate the surface defects but also can transfer energy to emissive CuInS2, thus thinning the thickness of inert shell greatly boost the detection sensitivity.