CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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4.2.2. Synthesis:
The CdTe QDs were prepared by water soluble methods as reported in the literature
[4.13]. Briefly, 2.35mmol of Cd(NO 3 ) 2 was added to nanopure water to this
mercaptopropionic acid (MPA) with the mole ratio of MPA: Cd=2.4:1. The pH of the above
solution was raised to 9-10 and was purged with N 2 . The tellurium precursor NaHTe, was
prepared by reaction between NaBH 4 and tellurium powder in N 2 purged water at 0 ◦ C for 8
hr. Part of this solution was added to the Cd precursor solution with the ratio of Cd:Te=1:0.5.
The above solution was refluxed and aliquots of the solution were removed at various times
to obtain quantum dots of different sizes. The aliquots were concentrated at lower pressure
by a Butchi rotavapour to 1/3 rd of the original volume and isopropyl alcohol was added to the
concentrated solution to precipitate the quantum dots. The collected quantum dots were redissolved
in nanopure water and precipitated with isopropyl alcohol, this process was
repeated 3 times to remove the precursors and clean the quantum dots.
The concentration of CdTe samples was ~10 -5 M as calculated from extinction
coefficient from Peng et al [15] at the exciton peak position. The =jσ value was
maintained at ~0.1excitons per particle to avoid multi particle relaxation processes like
Auger process involving 3 charge carriers. Four CdTe samples were prepared and are
abelled according to increasing size CdTe1 (2.6nm), CdTe2 (3.3nm), CdTe3 (3.5nm) and
CdTe4 (3.8nm).