Synthesis and Characterization of a Size Series of Extremely Small Thiol-Stabilized CdSe Nanocrystals

Abstract

As an expansion to the wet chemical route for the preparation of quantum-sized II-VI semiconductor materials, a series of thiol-capped crystalline CdSe nanoparticles has been synthesized in aqueous solution using mercaptoalcohols (2-mercaptoethanol, 1-thioglycerol), and mercapto acids (thioglycolic acid, thiolactic acid) as stabilizers. The smaller (app. 1.4-2.2 nm diameter) CdSe particles were obtained using thioalcohols as capping agents; the use of thioacids as stabilizers produced larger (2.1-3.2 nm diameter) CdSe particles. CdSe nanoparticles were separated from the crude solutions as redissolvable powder samples with narrow size distributions using a size-selective fractionation and have been characterized by UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis. A calculation of the HOMO-LUMO gap of CdSe particles as a function of their size has been done using an extended effective mass approximation.

Influence of Thiol Capping on the Exciton Luminescence and Decay Kinetics of CdTe and CdSe Quantum Dots

“…Capping exchange with thiols affects the luminescence properties of CdSe QDs in a way remarkably different from that observed for CdTe QDs. Thiols that yield a high QE and a monoexponential decay for CdTe QDs are observed to almost completely quench the luminescence of CdSe (see above and also refs [12][13][14][15][16]. This difference is particularly remarkable considering that the two II-VI semiconductors are chemically similar and have comparable band gap energies.…”

“…12 In contrast we have recently prepared water-soluble, thiolcapped CdTe QDs with a high efficiency (up to 60%) and a monoexponential decay, 13 demonstrating that the capping exchange with thiols has a beneficial effect on the quantum efficiency (QE) for CdTe QDs. Highly efficient thiol-capped CdTe QDs have also been reported by Weller and coworkers, 14,15 in striking contrast with the weakly luminescent thiol-capped CdSe QDs reported by the same group. 16 It is the purpose of this paper to understand the remarkable difference between the luminescence behavior of these two related semiconductors upon binding to thiols.…”

Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin

“…35 To this end CdTe QDs are attractive candidates due to their relatively narrow band gap (~1.7 eV) and the emergence of routine aqueous based synthetic methods. 17 However, only a handful of studies have probed the charge and energy dynamics of CdTe QDs on the ultrafast timescale and even fewer have 40 considered how these dynamics are influenced by the presence of suitable electron donor or acceptor surface species. [18][19][20][21][22][23][24][25][26] Due to the role in natural photosynthesis of related compounds porphyrin molecules have been extensively exploited for electron and energy transfer.…”

Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod Morphologies

“…These can be obtained by reacting cadmium and selenium precursors in the presence of the stabilizing agents trioctylphosphine oxide (TOPO), trioctylphosphine (TOP) and hexadecylamine (HDA) at high temperatures, typically above 300°C [1,13]. Recently CdSe nanocrystals with a cubic (zinc-blende) structure (further referred to as "zb-CdSe") have been synthesized by several groups [14][15][16]. In this work we compared w-CdSe and zb-CdSe nanocrystals for seeded growth of CdSe/CdS nano-hererostructures with different morphologies.…”