Chemical synthesis and optical characterization of regular and magic-sized CdS quantum dot nanocrystals using 1-dodecane
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Michael Z. Hua) Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6181, USA (Received 2 January 2015; accepted 17 February 2015)
Cadmium sulfide (CdS) quantum dot (QD) nanoparticles have been synthesized using a one-pot noninjection reaction procedure in solvent medium 1-octadecene. This approach used a cadmium salt and 1-dodecanethiol, an organic sulfur, as the cadmium and sulfur sources, respectively, along with a long-chain organic acid (myristic acid, lauric acid, or stearic acid). The acid has dual effects as a surface capping ligand and a solubility controlling agent as well. UV–Vis and photoluminescence (PL) spectrometry techniques were used to characterize the optical properties, along with transmission electron microscopy (TEM) to identify the structure and size. Our newly developed synthesis procedure allowed for investigation of both regular and “magic-sized” CdS QDs by systematically controlling reaction parameters such as reactant type, reactant concentration, and reaction temperature. The organic sulfur (1-dodecanethiol) proved to be a useful sulfur source for synthesizing magic-sized CdS QDs, previously unreported. Several distinctive size regimes of magic-sized quantum dots (MSQDs), including Families 378 and 407, were successfully produced by controlling a small number of factors. The understanding of controlled Cd release in a MSQD formation mechanism is developed.
I. INTRODUCTION
Semiconductor quantum dots (QDs) have shown many valuable applications in energy-efficient lighting, solar cells, and biolabeling and imaging.1–3 Their unique optical properties fall between those of bulk semiconductors and individual particles due to quantum confinement, and as a result, those properties correspond directly to the size of the QDs.3–5 This relationship provides the potential for highly specific, tunable nanocrystals of different size regimes.5,6 Several approaches to synthesize high-quality QDs, including CdS, CdTe, ZnS, ZnO, and Ag2S, have been developed that result in nanocrystals with some size distribution.4–11 However, the need for single-sized QDs has led to research in producing so-called “magic-sized” quantum dots (MSQDs) exhibiting narrow photoluminescence (PL) peak and unshifting absorption spectra throughout synthesis. These MSQDs appear at fixed absorption peak wave length (nm) positions as a result of homogeneous nucleation and uniformly sized products without further growth; contrasting “regular” QDs, whose particle sizes increase, or grow, with time throughout synthesis period. The nanocrystal growth is evidenced by a continuous red-shift of Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. email: [email protected] DOI: 10.1557/jmr.2015.57 890
J. Mater. Res., Vol. 30, No. 7, Apr 14, 2015
http://journals.cambridge.org
Downloaded: 17 Apr 2015
absorption peak with time for each synthesis batch.2,12–14 Several previous works have shown the ability to produce MSQDs, with CdS and other semiconducting materials, using various approaches. These methods allow for
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