Greener synthesis and optimization of highly photoluminescence
Mn
2þ
-doped ZnS quantum dots
Chunyan Zhou, Jiahui Song, Liya Zhou
n
, Liping Zhong, Jiaxian Liu, Yaya Qi
School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
article info
Article history:
Received 10 March 2014
Received in revised form
22 September 2014
Accepted 23 September 2014
Available online 14 October 2014
Keywords:
Quantum dots
Luminescence
Nanocrystals
abstract
In this study, ZnS quantum dots (QDs) and strong yellow light-emitting Mn
2þ
-doped ZnS QDs are
synthesized using 3-mercaptopropionic acid (MPA) as a stabilizer by a promising preparation method in
an aqueous solution. Further, the photoluminescence (PL) properties of the ZnS QDs under different
conditions are thoroughly investigated. Under optimized experimental conditions, the structure of the
obtained ZnS:Mn
2 þ
nanocrystals is consistent with that of the cubic zinc blende crystal, with a nearly
spherical shape of approximately 5 nm average diameter. The emission peak varies from 450 nm to
575 nm with Mn
2þ
doping, which suggests effective energy transfer from the host ZnS QDs to the
dopant Mn
2þ
ions. The results indicate that ZnS:Mn
2þ
QDs can potentially be used in light-emitting
diodes (LEDs).
& 2014 Elsevier B.V. All rights reserved.
1. Introduction
Semiconductor nanocrystals, or so-called quantum dots (QDs)
have attracted more and more attention in optoelectronic, symme-
trical and tunable emission profiles, high quantum yields as robust
fluorescent materials, which make them suitable for wide applica-
tions [1–3]. Furthermore, Cd-based II–VI QDs have excellent attri-
butes in the optical properties, which can be tuned by size and
composition in the fabrication of white light-emitting diodes (LEDs)
[4]. But one major drawback that severely limits the use of CdSe in
the light of recent environmental regulations, particularly in bio-
medical applications, is their inherent toxicity [5,6].Therefore,the
emphasis has shifted toward the fabrication of non-cadmium-based
QDs. Currently, wide band gap zinc chalcogenides semiconductor
nanocrystals, doped with transition metal ions (mainly Mn
2þ
), may
not only overcome this concern, but also maintain the advantages of
the nanocrystal emitters [7,8].
ZnS, a typical II–VI wide band gap semiconductor (3.6 7 eV), is
particularly suitable as a host material for a large variety of dopants.
Since Bhargva et al. [9] first r eported the synthesis of Mn
2þ
-doped
ZnS nanoparticles in 1 994, many researchers have reported the doped
nanoparticles via a wide v ariety of methods, such as organometallic
synthesis, microwave assisted growth [1 0], reverse micelle route [11]
and the precipitation reaction method [12] . Howev er , QDs thus
produced usually suffer some pr oblems such as stringent laboratory
conditions (high temperature), poor crystallinity, poor water-solubility
and less size controllability , which significantly hinder their potential
applications. An aqueous phase synthesis method is a promising
alternative route in these researches which offers certain advantages,
such as lower cost, lower to xicit y , and simplicity. For example, Wang
et al. introduced a hydrothermal method in preparation for the
Mn
2þ
-doped ZnS to eliminate the need of N
2
protection [1 3].An
aqueous method f or obtaining glutathione-capped Mn
2þ
-doped ZnS
QDs is also reported [1 4].
This paper focuses on a promising one-step method for the
synthesis of high-quality water-soluble ZnS:Mn
2 þ
quantum dots,
which provides a lower-cost and friendlier procedure for the
preparation. The results show improved fluorescence property,
indicating their potential application in LED. The influence of
process variables on optical properties of Mn
2 þ
-doped ZnS nano-
crystals is discussed in detail.
2. Experimental
2.1. Materials
Zn(CH
3
COO)
2
2H
2
O (A.R.), Na
2
S 9H
2
O (A.R.), MnCO
3
(A.R.),
and 3-mercaptopropionic acid (MPA, 99%) were used to prepare
the ZnS:Mn
2 þ
nanocrystals.
2.2. Synthesis of Mn
2 þ
-doped ZnS nanoparticles
ZnS:Mn
2þ
QDs were prepared in an aqueous solution. In a
typical procedure, 96 mL of 0.02 mol L
1
Zn(OAc)
2
2H
2
Osolution
Contents lists available at ScienceDirect
journ al home page: www.elsevier.com/locate/jlumin
Journal of Luminescence
http://dx.doi.org/10.1016/j.jlumin.2014.09.053
0022-2313/& 2014 Elsevier B.V. All rights reserved.
n
Corresponding author. Tel./fax: þ 86 771 3233718.
E-mail address: zhouliyatf@163.com (L. Zhou).
Journal of Luminescence 158 (2015) 176–180