A Two-Step Method To Synthesize Water-Dispersible Mn:ZnSe Quantum Dots And The Analysis Of Its Fluorescence Properties

Luminescent QDs have attracted a lot of attention due to their unique optical properties and enormous applications. In the past two decades, Ⅱ-Ⅵ QDs, such as CdSe, CdS, and CdTe, have developed into the workhorse in the QD family due to their good optical properties such as narrow and symmetric emission with tunable colors, broad and strong absorption, and reasonable stability, in the visible light scope. However, the intrinsic toxicity of Cd-containing QDs is a potential problem limiting their applications. In recent developments, wide-band-gap semiconductor QDs such as ZnS and ZnSe doped with transition ions (Mn or Cu) have attracted considerable attention. These QDs not only retain almost all of the above advantages of Cd-containing QDs, but also avoid the self-quenching problem.Currently, a variety of synthetic approaches have been developed to QDs, mostly focused on two main methods. The first one is an organometallic method, which can produce Mn:ZnSe QDs with good monodisperse and high PL QY in organic medium. Due to hydrophobic ligands capped on the surface, as-prepared QDs are only dispersible in organic solvents before handling such as ligand exchange, making them unsuitable for bio-applications directly. The second one is an aqueous synthesis method, which has been proven to be a simpler, cheaper, and less toxic method to prepare water-dispersible QDs.In this paper, water-dispersible Mn:ZnSe/ZnO core/shell quantum dots (QDs) with pure dopant emission were prepared via a two-step method. Compared with the traditional organometallic approach, this two-step method has many advantages, such as using low-cost and non-toxic chemicals, low reaction temperature and simple operation. Moreover, the obtained Mn:ZnSe/ZnO core/shell QDs also showed superior properties to those prepared by the aqueous solution synthesis, such as narrow emission and good monodispersity. The influence of the storage time of Mn:ZnSe QDs in organic medium, the amount of MPA and temperature during the period of ZnO shell deposition on the photo-luminescence (PL) properties was investigated. Under optimal conditions, MPA-capped Mn:ZnSe/ZnO QDs with a dopant PL quantum yield (QY) of 30% in water were produced. On this basis, Cu-Mn co-doped multilayer Mn:ZnSe/Cu:ZnO QDs were prepared. Mn:ZnSe/Cu:ZnO QDs have two emission bands. Finally, CuInS2/ZnO QDs were also prepared.