Highly Luminescent Water-Soluble CdTe Quantum Dots

Abstract

Colloidal CdTe quantum dots prepared in TOP/DDA (trioctylphosphine/dodecylamine) are transferred into water by the use of amino− ethanethiol•HCl (AET) or mercaptopropionic acid (MPA). This results in an increase in the photoluminescence quantum efficiency and a longer exciton lifetime. For the first time, water-soluble semiconductor nanocrystals presenting simultaneously high band-edge photoluminescence quantum efficiencies (as high as 60% at room temperature), monoexponential exciton decays, and no observable defect-related emission are obtained.

Influence of Thiol Capping on the Exciton Luminescence and Decay Kinetics of CdTe and CdSe Quantum Dots

“…The higher luminescence efficiency is ascribed to a better surface passivation by the thiol capping molecules. For CdTe QDs with an optimized QE after synthesis in TOP/ DDA, capping exchange with AET has been shown to yield water-soluble QDs with a QE as high as 60% 13 which is in agreement with the presently observed beneficial effect of capping exchange with a variety of thiol molecules.…”

“…This defect-related emission originates from surface defects since recapping with AET removes this type of emission almost completely. 13 This defect-related emission is also observed in efficient samples since the QDs are not all chemically identical.…”

“…DDA capping molecules (bound to the Cd sites of the CdTe QD) are not very strongly bound capping molecules compared to, for instance, thiols. 13 Therefore exchange of the DDA surface molecules for thiols takes place rapidly. This is reflected in the fast precipitation of the QDs after AET addition and the immediate increase in the luminescence intensity and the luminescence decay time upon hexanethiol addition (see below).…”

Aqueous phase synthesis of CdTe quantum dots for biophotonics

“…To date, most of the reported X-ray diffraction profiles of CdTe QDs prepared in the water have shown that they have the zinc blende crystal structure [46]. Three strong peaks will generally be observed with 2q values at 23.7 , 39.3 and 46.4 corresponding to the (111), (220), and (311) planes [47]. The peak at 23.7 will generally be more intense than the other two peaks.…”

“…Several surfactants have been used for synthesizing CdTe quantum dots in the aqueous phase, namely, thioglycolic acid (TGA) [48][49][50], mercaptopropionic acid (MPA) [47], mercaptosucinnic acid (MSA) [51][52], glutathione (GSH) [53], and cysteine (Cys) [54]. TGA, MPA, and MSA are short stabilizing agents and they are commonly used to fabricate water-dispersible CdTe QDs in a one-pot synthesis.…”