Spectroscopy of Single CdSe Magic-Sized Nanocrystals

Magic-sized nanocrystals (MSNCs) are semiconductor crystallites that grow in discrete steps. They lead to samples that potentially contain a single size and shape (i.e., monodisperse). To understand the impact of "magic" sizes on optical performance, we study the emission of individual MSNCs at room temperature. We find that the single-MSNC line width dominates ensemble emission spectra. By examining MSNCs with different sizes and shells, we conclude that the observed single-particle line is consistent with coupling of excitons to acoustic surface phonons. This coupling and any residual size dispersity influence MSNCs more than standard quantum dots, which experience weaker confinement. When CdSe quantum dots with similar confinement are compared with small CdSe MSNCs (<2.7 nm diameter), MSNCs have narrower ensemble spectra. Our MSNCs are bright emitters (40-80% efficient) with strong photon antibunching [g⁽²⁾(0) ∼ 0.05], making them promising candidates for applications in optoelectronics and quantum information, where strong three-dimensional confinement is required.