Heterogeneity in Cation Exchange Ag+ Doping of CdSe Nanocrystals

Tunable and Orange to Near-Infrared Doped Photoluminescence of Ag-Doped II-VI QDs

The electronic doping of colloidal semiconductor nanocrystals presents significant potential for future device concepts in optoelectronic and spin-based technologies. Ag+ is gaining recognition as a novel electronic dopant in II-VI nanocrystals as it creates intragap electronic states that participate in the recombination process of photogenerated carriers within the host materials. Herein, we report the synthesis of a series of Ag-doped II-VI quantum dots (QDs) of varying sizes via a low-temperature cation exchange strategy. A surprisingly tunable dopant emission covering the orange to near-infrared window (606-725 nm for CdS/Ag and 745-877 nm for CdSe/Ag) is achieved through the manipulation of particle sizes in the host QDs, which is derived from the quantum confinement effect. The as-prepared Ag+-doped II-VI QDs exhibit effective size-dependent tunable emission with a quantum yield (QY) up to 40.7% and strongly suppressed reabsorption due to the large Stoke shift up to 0.86 eV, demonstrating their potential use as candidates for various optoelectronic devices. Furthermore, using CdSe/Ag as a case to study, both experimental results and density functional theory (DFT) calculations indicate that the successful Ag+ doping in the matrix not only results in the formation of additional extra luminescence centers but also causes a reduction in the bandgap.

Silver-doped CdSe magic-sized nanocrystals

Magic-sized nanocrystals (MSNCs) grow via jumps between very specific sizes. This discrete growth is a possible avenue toward monodisperse nanomaterials that are completely identical in size and shape. In spite of this potential, MSNCs have seen limited study and application due to their poor optical properties. Specifically, MSNCs are limited in their range of emission wavelengths and commonly exhibit poor photoluminescence quantum yields (PLQYs). Here, we report silver doping of CdSe MSNCs as a strategy to improve the optical properties of MSNCs. Silver doping leads to controllable shifts in emission wavelength and significant increases in MSNC PLQYs. These results suggest that doped MSNCs are interesting candidates for displays or luminescent solar concentrators. Finally, we demonstrate that the doping process does not affect the magic size of our MSNCs, allowing further photophysical study of this class of nanomaterial.