Nanoparticles, Nanocrystals, and Quantum Dots: What are the Implications of Size in Colloidal Nanoscale Materials?

Semiconductor nanoparticles (NP) or nanocrystals (NC) have been investigated for many decades, with particular acceleration in interest upon the discovery of quantum confinement effects thereby yielding quantum dots (QD) from certain well-grown NC. The term NP is commonly used in the case of metal and wide gap semiconductor nanocrystals. The term NC is commonly used in semiconductor nanocrystals, whether covalent II-VI or ionic perovskites, that are colloidally grown. The term QD applies to select semiconductor nanocrystals for whom their size is on the order of the excitonic Bohr radius. In the case of colloidal particles on the nanometer length scale, these terms are often used carelessly and interchangeably. The words have specific meaning in relationship to specific physical effects which give rise to specific key processes that can be measured. Here, we provide a Perspective on the ways in which size confers function across different families of NP. In this way, we aim to find ways to identify their similarities and differences by providing the correct semantics for discussion of the salient processes.