Res. Chem. Intermed.
, Vol. 31, No. 7–8, pp. 691–702 (2005)
Also available online - www.vsppub.com
Synthesis and spectral studies of cysteine-capped
, A. CHATTERJEE
and A. SAHA
Inter University Consortium for Scientiﬁc Research, Kolkata Centre, III/LB-8 Bidhannagar,
Kolkata 700 098, India
Variable Energy Cyclotron Centre, I/AF Bidhannagar, Kolkata 700 064, India
Received 31 March 2004; accepted 10 June 2004
Abstract—Highly water-soluble and biocompatible cysteine-capped CdS nanoparticles have been
synthesized in the colloidal state, and particle distribution has been narrowed down using the size-
selective precipitation technique. Optical absorption and emission spectra conﬁrm that particles
formed lie within the size quantization regime. An enhancement in luminescence has been observed
on addition of free Cd
ions and cysteine to the solution of CdS nanoparticles. The pH dependence
of the ﬂuorescence has also been studied.
Keywords: Cadmium sulphide; quantum dots (QDs); nanoparticles (NPs); quantum conﬁnement; size-
selective precipitation; absorption onset.
Semiconductor nanocrystals or colloidal quantum dots (QDs) have generated great
research interest in the past two decades because of their unique size-dependent
photophysical and photochemical properties [1, 2]. From the viewpoint of basic
science, a nanocrystal is an intermediate state of matter between molecule-like
clusters and bulk crystals, and, therefore, can help in tracing the evolution of
electronic and optical properties of matter from small atomic clusters to bulk solids.
Prominent among the unusual properties of these semiconductor nanocrystals is the
blue shift in the onset of optical absorption spectra. This can be understood in terms
of quantum-conﬁnement effects [3–9].
Several studies in this ﬁeld focus on the development of new cost effective
techniques to synthesize high-quality QDs and to measure photophysical and
photochemical properties in the aqueous phase. A good synthetic route should
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