Lanthanide Modification\nof CdSe/ZnS Core/Shell Quantum\nDots

Abstract

Lanthanide-modified CdSe quantum dots (CdSe­(Ln) QDs)\nhave been\nprepared by heating a solution of Cd­(oleate)₂, SeO₂, and Ln­(bipy)­(S₂CNEt₂)₃ (bipy\n= 2,2′-bipyridine) to 180–190 °C for 10–15\nmin. The elemental compositions of the resulting CdSe­(Ln) cores and\nCdSe­(Ln)/ZnS core/shell QDs show this route to be highly reproducible.\nThe optical absorption spectra of these composite materials are similar\nto those of the unmodified nanocrystals, but the QD-centered band\nedge photoluminescence (PL) is partially quenched. The time-gated\nemission and excitation spectra of the CdSe­(Ln) cores display sensitized\nlanthanide-centered PL upon higher energy excitation of the nanocrystal\nhost but not upon excitation at the lowest energy QD absorption band.\nGrowth of the ZnS shell led to the depletion of about 60% of the lanthanide\nions present together with depletion of nearly all of the lanthanide-centered\nPL. On these bases, we conclude that the lanthanide-centered PL from\nthe CdSe­(Ln) cores originates with Ln³⁺-related trap states\nassociated with the QD surface.