(214f) Thermodynamically Driven Approach Toward Engineering Nanomanufacture of Single-Sized Colloidal Semiconductor Quantum Dot Nanocrystal Ensembles with Bandgap Photoluminescence

Colloidal photoluminescent (PL) semiconductor nanocrystals have attracted significant attention over the past decade for both fundamental sciences and potential applications. When the size of a nanocrystal becomes less than or comparable to that of a photogenerated exciton in bulk materials, the effect of quantum confinement becomes operative. Quantum dots (QDs) are spherical nanocrystals whose excitons are confined in three spatial dimensions, and thus can absorb and then emit light, size-dependently. Usually, the optical properties are size-dependent, with bandgap absorption and emission wavelength tunable (via size, structure, and composition). For example, the bandgap of CdSe QDs is tunable across the visible range (~ 400 nm to ~ 700 nm); thus, they are of particular interest for the study of fundamental physics with great potential in various applications. However, the size-dependent characteristics, which make regular quantum dots (RQDs) fascinating, create intrinsic difficulties to study; the variation in size within one colloidal ensemble sample gives rise to inhomogeneous spectral broadening, in addition to homogeneous spectral broadening. The synthesis of colloidal QDs typically requires source compounds, solvents as reaction media, and surfactants as surface ligands providing colloidal stability and surface passivation. Both hot-injection and non-injection-based approaches lead to colloidal nanocrystal ensembles with a certain degree of size distribution. It is a leading-edge and challenging task to design and synthesize colloidal nanocrystal ensembles free of inhomogeneous spectral broadening. At present, the formation mechanism of the nanocrystals is far from being understood.

This presentation addresses our latest advances in the synthesis of single-sized QDs exhibiting bandgap emission with only homogeneous spectral broadening. Such QDs are also called magic-sized QDs (MSQDs). The formation mechanism will be discussed, the investigation of which brings insights for the fundamental understanding of the nucleation and growth leading to the formation of RQDs and/or MSQDs, and for rational design strategies on reproducible, large-scale production of various compositions and multiple quantized families of MSQDs aiming at various applications including solar cells, solid-state lightings, and other optoelectronic devices. The opportunity in future engineering development of non-injection-based chemical nanomanufacturing processes will be also discussed.