Nanoshell quantum dots: Quantum confinement beyond the exciton Bohr radius

Abstract

Nanoshell quantum dots (QDs) represent a novel class of colloidal semiconductor nanocrystals (NCs), which supports tunable optoelectronic properties over the extended range of particle sizes. Traditionally, the ability to control the bandgap of colloidal semiconductor NCs is limited to small-size nanostructures, where photoinduced charges are confined by Coulomb interactions. A notorious drawback of such a restricted size range concerns the fact that assemblies of smaller nanoparticles tend to exhibit a greater density of interfacial and surface defects. This presents a potential problem for device applications of semiconductor NCs where the charge transport across nanoparticle films is important, as in the case of solar cells, field-effect transistors, and photoelectrochemical devices. The morphology of nanoshell QDs addresses this issue by enabling the quantum-confinement in the shell layer, where two-dimensional excitons can exist, regardless of the total particle size. Such a geometry exhibits one of the lowest surface-to-volume ratios among existing QD architectures and, therefore, could potentially lead to improved charge-transport and multi-exciton characteristics. The expected benefits of the nanoshell architecture were recently demonstrated by a number of reports on the CdSbulk/CdSe nanoshell model system, showing an improved photoconductivity of solids and increased lifetime of multi-exciton populations. Along these lines, this perspective will summarize the recent work on CdSbulk/CdSe nanoshell colloids and discuss the possibility of employing other nanoshell semiconductor combinations in light-harvesting and lasing applications.

Quantum Shells Boost the Optical Gain of Lasing Media

“…These nanomaterials disperse multiple excitons across a spherical shell layer and, therefore, can support longer multiexciton lifetimes. Unfortunately, the synthetic challenges associated with the colloidal fabrication of these layered QDs have previously hindered their optical-gain performance. , …”

Enabling Narrow Emission Line Widths in Colloidal Nanocrystals through Coalescence Growth

“…In addition to the classical, precursor-controlled synthesis, some reports − have demonstrated the existence of a fundamentally different growth mechanism, which involves the coalescence of already preformed nanoparticles in the reaction mixture. This process is recognized as an important mechanism contributing to the formation of metal nanoparticles − and is believed to play a significant role in the size evolution of semiconductor NCs.…”

Nanomaterials Application in Endodontics

“…It is present when a particle is too small to be comparable with electron wavelength. This is a general condition that is strictly limited by specific material properties, especially Bohr radius [20]. The density of states (DOS) can be explained as a model of 'particle in a box', where the size of the particle is directly proportional to the size of the box [21].…”