Thermodynamic Silver Doping of Core/Shell Colloidal Quantum Wells Imparted with Paramagnetic Properties Emitting at Near-Infrared

Two-dimensional (2D)core/shell nanoplatelets (NPLs)synthesizedvia the hot-injection method provide excellent thermal and chemicalstability for high-temperature doping, where an expanded and flexiblelattice is required. Here, a thermodynamic approach toward silverdoping of these NPLs is proposed and demonstrated, which previouslyproved to be challenging due to the fast self-purification of thedopants with the introduction of the shell. Maintaining the dopingprocedure in the reversible regime ensured the integrity of the NPLsand allowed a high level of doping; however, the equilibrium conditionis further complicated by environmental factors that affect the chemicalactivity of the cations and the surface composition of the NPLs. Twomain deterioration mechanisms in the irreversible regime were observed:ZnS-shelled NPLs suffered preferential etching, while CdS-shelledNPLs underwent cleavage and fragmentation. Alloying of the shell minimizedboth mechanisms for CdZnS-shelled NPLs and preserved the metastablestate of the NPLs, including their 2D shape and crystalline structure.Distribution of silver ions in the lattice of the NPLs directly affectedthe recombination dynamics and enabled fine-tuning of the near-infraredemission beside the exciton confinement. These silver-doped CdZnS-shelledNPLs are shown further to exhibit enhanced paramagnetic propertieswith Zeeman splitting and Brillouin-like bound-exciton polarizationas a function of the magnetic field, critical for spintronic applications.