ARTICLE
Enhanced stability and emission intensity of aqueous
CdTe/CdS core–shell quantum dots with widely tunable
wavelength
1
Hongyu Wang, Ling Xu, Ni Liu, Renqi Zhang, Jun Xu, Weining Su, Yao Yu, Zhongyuan Ma, Wei Li,
and Kunji Chen
Abstract: The stability and photoluminescence (PL) emission intensity of quantum dots (QDs) are particularly interesting for
various bioapplications. In this paper, monodisperse CdTe/CdS core–shell QDs were synthesized in aqueous phase. The size of
CdTe core and the thickness of CdS shell played important roles in the properties of CdTe/CdS QDs. Transmission electron
microscopy (TEM) images show that the average diameters of CdTe/CdS core–shell QDs increased to ⬃5 nm compared with that
of CdTe core QDs (⬃3.6 nm). X-ray diffraction patterns show that the CdTe/CdS core–shell QDs possess cubic zinc blende
structure. After the overgrowth of CdS shell on CdTe core, a widely tunable PL emission wavelength (485–720 nm) of the
core–shell QDs can be obtained, which covers nearly the full visible spectrum. The PL intensity of the CdTe/CdS core–shell QDs
shows two-fold increase compared with that of the CdTe core QDs. PL results show that the photostability of the samples is
enhanced through the growth of CdS on the CdTe QDs.
PACS Nos.: 78.55.Et, 82.33.Ln, 68.65.Hb.
Résumé : La stabilité et la photoluminescence (PL) de l’intensité d’émission des points quantiques (QD) sont particulièrement
intéressantes pour les bio-applications. Nous fabriquons ici en phase aqueuse des QD uniformes de cœur–coquille de CdTe/CdS.
La grosseur du cœur de CdTe et l’épaisseur de la coquille de CdS jouent un rôle important dans les propriétés du QD. La
microscopie par transmission électronique indique que le diamètre moyen du QD de cœur/coquille de CdTe/CdS augmente a
`
5 nm, comparé a
`
un QD de cœur de CdTe (3.6 nm). Les patrons de diffraction X montrent que le QD de cœur–coquille de CdTe/CdS
a une structure blende de zinc. La croissance de la coquille de CdS sur le cœur de CdTe nous permet d’obtenir un QD cœur–
coquille avec une émission PL largement accordable en longueur d’onde allant de 485 a
`
720 nm, couvrant pratiquement tout le
spectre visible. L’intensité PL d’un QD avec cœur–coquille CdTe/CdS est deux fois plus importante que pour un QD avec cœur de
CdTe. Les mesures PL indiquent que la photostabilité des échantillons est meilleure après l’ajout de la coquille de CdS sur le cœur
de CdTe du QD. [Traduit par la Rédaction]
1. Introduction
Colloidal semiconductor nanocrystals (known as quantum dots
(QDs)), especially II–VI QDs, have attracted great interest in solar
cell and various bioapplications because of their unique proper-
ties, such as narrow emission, excellent photochemical stability,
size-dependent emission wavelength, and broad excitation [1–3].
Over the past years, great progress has been made in preparing
QDs, such as CdTe [4] and CdS [5] were synthesized in aqueous
phrase or organic solvent. However, quantum yields of bare QDs is
low because of the defects on the surface. To improve the fluores-
cence efficiency and photostability of QDs, core–shell QDs were
synthesized by the growth of shell on the core [6–8], such as CdTe/
ZnSe [9], CdSe/ZnS [10], and CdTe/CdSe [11]. The synthesis of CdTe/
CdS core–shell QDs was also reported, but few investigations have
studied the photostability and the influence of the thickness of
CdS shell around the CdTe core on photoluminescence (PL) emis-
sion intensity of QDs.
In this work, 3-Mercaptopropionic acid (MPA)-capped CdTe core
QDs and corresponding CdTe/CdS core–shell QDs were synthe-
sized in aqueous solution. In particular we performed the exper-
iments on the influence of the shell thickness on the variations of
PL intensity and the wide PL emission window of CdTe/CdS core–
shell QDs. Finally we studied the photostability of the CdTe core
and corresponding CdTe/CdS QDs with different shell thick-
nesses.
2. Experimental
2.1. Chemicals
Tellurium powder (99.9%) and MPA (99%) were purchased from
Aldrich. Thioacetamide (TAA, 99%), sodium borohydride (NaBH
4
,
Received 19 October 2013. Accepted 18 March 2014.
H. Wang. National Laboratory of Solid State Microstructure and Jiangsu Provincial Key Laboratory of Photonic and Electronic Material Sciences and
Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People’s Republic of China; Nanjing University of Posts
and Telecommunications, Nanjing 210003, Jiangsu Province, People’s Republic of China.
L. Xu, N. Liu, R. Zhang, J. Xu, Z. Ma, W. Li, and K. Chen. National Laboratory of Solid State Microstructure and Jiangsu Provincial Key Laboratory of
Photonic and Electronic Material Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People’s
Republic of China.
W. Su and Y. Yu. National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People’s Republic
of China.
Corresponding authors: Ling Xu (e-mail: xuling@nju.edu.cn) and Wei Li (e-mail: Weili@nju.edu.cn).
1
This paper was presented at the 25th International Conference on Amorphous and Nanocrystalline Semiconductors (ICANS25).
802
Can. J. Phys. 92: 802–805 (2014) dx.doi.org/10.1139/cjp-2013-0557
Published at www.nrcresearchpress.com/cjp on 16 June 2014.
Can. J. Phys. Downloaded from www.nrcresearchpress.com by Nanjing University on 12/25/15
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