Doping of Mn²⁺ into Aqueous ZnSe Nanocrystals with Pure Dopant Emission through a Light-Induced Electrostatic Attraction and Diffusion Method

Although Mn2+-doped aqueous ZnSe nanocrystals (NCs) have been reported, the obtained doped NCs usually possess multiple emission peaks originated from nanocrystal bandgap, defects, and Mn-dopants. It is difficult to obtain water-soluble ZnSe nanocrystals with pure Mn-dopant emission by traditional synthesis method. In this work, a new light-induced method of doping Mn2+ ions into ZnSe NCs is demonstrated to obtain doped ZnSe NCs with pure Mn-dopant emission. The electrostatic attraction between photogenerated electrons and Mn2+ cations is considered to be the driving force of Mn2+ diffusion and doping. The possible mechanism of incorporating Mn dopants into ZnSe NCs is proposed and verified. The successful doping of Mn into ZnSe NCs may go through three processes. (1) Process 1: Generation of electrons and holes by UV light irradiation. (2) Process 2: Consuming photogenerated holes by hole scavengers, leaving photogenerated electrons inside NCs. (3) Process 3: Diffusion of Mn2+ inside ZnSe lattice, resulting in patched inner defects. In contrast with reported diffusion-doping method which involves addition of stoichiometric cations and anions, the current light-induced doping only needs cation addition. Therefore, only a slight change of the NC size is observed. The current Mn2+-doped ZnSe NCs are temperature sensitive and may have potential use for temperature detection.