Acceleration of Near-IR Emission through Efficient Surface Passivation and Doping of Cd₃P₂ Quantum Dots

Fast near-IR (NIR) emitters are highly valuable in telecommunications and biological imaging. Colloidal synthesis is a potent method that produces a few NIR-emitting materials, but they suffer from long photoluminescence (PL) times. These long PL times are intrinsic in some NIR materials (PbS, PbSe) but are attributed to emission from bright trapped carrier states in others. We develop the colloidal chemistry of an overlooked II–V semiconductor cadmium phosphide (Cd₃P₂) — an alternative promising near-IR material that offers a high bandgap tunability. It is a unique material that bridges III–V and II–VI semiconductors and combines the best of both worlds: near-IR emission with solution processability. We show that as-synthesized Cd₃P₂ QDs possess substantial trap emission with radiative times >10¹ ns. With the help of intelligent surface passivation through shell growth or Lewis coordination, or through cationic doping, we manage to accelerate the NIR emission from Cd₃P₂ QDs by decreasing the amount of trap emission. This finding brings us one step closer to the application of colloidally synthesized QDs as quantum emitters.