Tunable and Efficient Red to Near-Infrared Photoluminescence by Synergistic Exploitation of Core and Surface Silver Doping of CdSe Nanoplatelets

We report on the synthesis of silver (Ag)-doped CdSe nanoplatelets (NPLs) via postsynthesis cation exchange, using silver acetate as the Ag precursor. High-resolution transmission electron microscopy and X-ray diffraction confirmed that the NPLs maintain their morphology and crystal structure after doping when executing the exchange under reduced temperature in an ice bath. Spectroelectrochemistry and transient absorption spectroscopy revealed that Ag+ acts as an acceptor dopant. Ag doping results in an emission that is tunable from 609 to 880 nm, with a Stokes shift up to 1 eV and a photoluminescence quantum efficiency exceeding 50%. This is achieved by varying the Ag dopant concentration, which determines the hole energy level, and by controlling the electron energy level via quantum confinement in CdSe NPLs with varying core thickness or in CdSe/CdS core/shell NPLs. As highly fluorescent materials with a strongly suppressed emission reabsorption because of the large Stokes shift, Ag-doped colloidal two-dimensional NPLs offer new opportunities for the development of colloidal nanocrystal-based optoelectronic and photonic devices such as light-emitting diodes or luminescent solar concentrators.