Energy transfer in near-infrared photoluminescent PbS/CdS quantum dot-based three-dimensional networks and films.

Nanocrystal (NC) assemblies, such as films or NC-based three-dimensional networks, provide insight into the nanoscopic properties of their building blocks, and are macroscopic materials. In NC assemblies in general, interactions between the building blocks have to be considered, since a decrease of the distance between the NCs allows phenomena such as energy transfer to occur. Novel quantum dot-based aerogels with optical properties in the near-infrared (NIR) region are not characterized in terms of these important properties in the literature, while the structural complexity of these networks raises questions about the interactions within. Since knowledge about the physical phenomena is vital for applications, we here investigate the photoluminescence (PL) of PbS/CdS QD-based assemblies, namely drop-cast films and aerogels with steady-state measurements at cryogenic temperatures and time-resolved measurements at room temperature. We find multiple emissive in-gap states (IGS), and a correlation between the number of nearest QD neighbors, the distance between the QDs in the assemblies and the non-radiative recombination rate by linking the observations to different energy transfer phenomena.