The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR)-active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intraband relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from the CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core–shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogeneous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe and the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.

Hybrid lead chalcogenide (PbE) (E = S, Se) quantum dot (QD)-layered 2D systems are an emerging class of photodetectors with unique potential to expand the range of current technologies and easily integrate into current complementary metal-oxide-semiconductor (CMOS)-compatible architectures. Herein, we review recent advancements in hybrid PbE QD-layered 2D photodetectors and place them in the context of key findings from studies of charge transport in layered 2D materials and QD films that provide lessons to be applied to the hybrid system. Photodetectors utilizing a range of layered 2D materials including graphene and transition metal dichalcogenides sensitized with PbE QDs in various device architectures are presented. Figures of merit such as responsivity (R) and detectivity (D*) are reviewed for a multitude of devices in order to compare detector performance. Finally, a look to the future considers possible avenues for future device development, including potential new materials and device treatment/fabrication options.