Since their discovery in 1981 by Alexey I. Ekimov, semiconductor nanocrystals (NCs) have seen a tremendous development and they are now exploited in the consumer electronics market. Colloidal semiconductor NCs present remarkable properties for the fabrication of a variety of photonic applications such as: light-sources, solar cells, X-rays scintillators and detectors. Colloidal semiconductor NCs are synthetized via wet chemistry approaches that offer an endless amount of freedom on the parameters that determine their optoelectronic properties such as crystal size, shape, crystallinity, chemical composition and architectures.

In this talk, I will present how we are focusing on the development of near-infrared (NIR) emitting NCs[1-4], NIR-LEDs[1] and single photon emitters (SPEs) based on isolated NC. NIR emitting NCs and their respective LEDs are of interest for a variety of optoelectronic applications such as hyperspectral and biomedical imaging, night vision and telecommunication systems. Up until now, all efficient NIR NCs are based on toxic heavy metals compositions while The European Union’s “Restriction of Hazardous Substances” (RoHS) directive limits the use of such compounds. Colloidal indium arsenide and lead-free perovskite NCs are emerging as promising candidate for NIR applications thanks to their low toxicity and recent progresses in material synthesis leading to stable and highly efficient NCs. We exploited InAs/ZnSe core-shell NCs to produce NIR-LEDs emitting in the range of 800-1000 nm,[1] while we developed cesium manganese bromide NCs that can be employed as sensitizers for broadband Vis-to-NIR downshifting.[3] Last but not least, these NCs are of interest for the fabrication of SPEs operating in the NIR; yet, study of their emission properties has just begun.

Another important property of NCs is their capability to operate as a SPE. Yet, complex small-footprint devices based on single NCs require controlled placement of isolated NCs on a planar surface to exploit NCs in the emerging fields of quantum communication, computing, and encryption, where optically pumped quantum dots are quickly gathering attention. A whole range of techniques have been explored to control the placing of colloidal NCs from solution on a solid substrate, exploiting e.g., chemical/wettability contrast between different areas of the substrate or other chemical physical interactions. We have applied capillary assembly  (a method that exploits the force exerted on NCs at the interface between the moving meniscus of the solution solvent and a solid substrate) to entrap a NC in pre-patterned holes on the surface, typically realized by means of lithographic methods such as electron beam lithography. The large area arrays we fabricate contain hundreds of single NCs, and we correlated the morphological data collected by scanning electron microscopy with optical data to unveil how the effective density of SPEs depends on an interplay between NC photoluminescence quantum yield and Poisson statistics of the nanohole filling process.