CdS magic-size clusters exhibiting one sharp ultraviolet absorption singlet peaking at 361 nm

We report, for the first time, the synthesis of CdS magic-size clusters (MSCs) which exhibit a single sharp absorption peaking at ∼ 361 nm, along with sharp band edge photoemission at ∼ 377 nm and broad trap emission peaking at ∼ 490 nm. These MSCs are produced in a single-ensemble form without the contamination of conventional quantum dots (QDs) and/or other-bandgap clusters. They are denoted as MSC-361. We present the details of several controlled syntheses done in oleylamine (OLA), using Cd(NO3)2 or Cd(OAc)2 as a Cd source and thioacetamide (TAA) or elementary sulfur (S) as a S source. A high synthetic reproducibility of the reaction of Cd(NO3)2 and TAA to single-ensemble MSC-361 is achieved, the product of which is not contaminated by other bandgap clusters and/or QDs. In some cases, the reaction product exhibits an additional absorption peak at ∼ 322 nm. We demonstrate that the two peaks, at 361 and 322 nm, do not evolve synchronously. Therefore, the 322 nm peak is not a higher order electronic transition of MSC-361, but due to the presence of another ensemble, namely MSC-322. The present study suggests that there is an outstanding need for the development of a physical model to narrow the knowledge gap regarding the electronic structure in these colloidal semiconductor CdS MSCs.