CdS Magic-Sized Nanocrystals Exhibiting Bright Band Gap Photoemission via Thermodynamically Driven Formation

Abstract

CdS magic-sized nanocrystals (MSNs) exhibiting both band gap absorption and emission at 378 nm with a narrow bandwidth of ∼9 nm and quantum yield (QY) of ∼10% (total QY ∼28%, in hexane) were synthesized via a one-pot noninjection approach. This CdS MSN ensemble is termed as Family 378. It has been acknowledged that magic-sized quantum dots (MSQDs) are single-sized, and only homogeneous broadening contributes to their bandwidth. The synthetic approach developed is ready and highly reproducible. The formation of the CdS MSQDs was carried out at elevated temperatures (such as 90−140 °C) for a few hours in a reaction flask containing bis(trimethylsilyl)sulfide ((TMS)2S) and Cd(OAc)(OA) in situ made from cadmium acetate dihydrate (Cd(OAc)2·2H2O) and oleic acid (OA) in 1-octadecene (ODE). Low OA/Cd and high Cd/S feed molar ratios favor this formation, whose mechanism is proposed to be thermodynamically driven. 13C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) demonstrates that the capping ligands are firmly attached to the nanocrystal surface via carboxylate groups. With the cross-polarization from 1H of the alkyl chains to surface 113Cd, 113Cd NMR is able to distinguish the surface Cd (471 ppm) bonding to both −COO− and S and the bulk Cd (792 ppm) bonding to S only. DOSY-NMR was used to determine the size of Family 378 (∼1.9 nm). The present study provides strategies for the rational design of various MSNs.

Turning “on” and “off” nucleation and growth: Microwave assisted synthesis of CdS clusters and nanoparticles

“…The TEM measurements help to set an upper limit of 1.6 AE 0.3 nm on the size of stable nuclei formed in the process. The absorption spectrum of nanocrystalline CdS NP measuring about 1.9 nm has been recently reported by Li and coworkers [30]. The absorption spectrum of 1.9 nm CdS NP exhibits a single band centered at 375 nm: bands at 322, 351 and 378 nm are observed in the time profile of the synthesis of the nanoparticles and have been attributed to a different CdS species coexisting during the different stages of the synthesis.…”

Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

“…26 At present, it is still challenging to accurately obtain the size information of small NCs. [27][28][29] Accordingly, for small-sized NCs, the use of their first excitonic absorption peak positions instead of their sizes can be practical to minimize the confusion in the size determination. 5 The first synthesis of colloidal PbSe QDs was reported in 2001 with a hot-injection approach.…”

Probing intermediates of the induction period prior to nucleation and growth of semiconductor quantum dots

“…A number of synthetic approaches have been documented that typically involved a laborious trial-and-error scheme to produce colloidal semiconductor CdTe (refs 31, 32, 33, 34), CdSe (refs 34, 35, 36, 37, 38, 39, 40, 41, 42), CdS (refs 43, 44) and other composition MSCs45464748. These studies did not address the formation pathway of the MSCs, although some did propose that the MSCs were the actual nuclei for the growth of NCs13384347.…”