Phosphine-free synthesis of ZnSe:Mn and ZnSe:Mn/ZnS doped quantum dots using new Se and S precursors

Abstract

ZnSe:Mn and core–shell ZnSe:Mn/ZnS doped quantum dots (d-dots) have been synthesized by using the alkylamine–H₂Se complex and thiourea as new phosphine-free Se and S precursors, respectively. Absorption spectroscopy, steady-state (solution and solid-state) and time-resolved photoluminescence spectroscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy were used to characterize the resulting d-dots. Results showed that Mn²⁺ was successfully doped and mainly distributed in the middle layer of the actual ZnSe/ZnSe:Mn/ZnSe d-dots and ZnSe/ZnSeS:Mn/ZnS d-dots which were simply referred to as ZnSe:Mn and core–shell ZnSe:Mn/ZnS d-dots with ZnSe and ZnS outmost shells, respectively. The increase in the intensity of phosphorescence from the dopant Mn²⁺ was obtained by the corresponding injection of Zn precursor or Zn/S precursors for ZnSe or ZnS shell growth. As compared to the ZnSe shell, the ZnS shell was grown more significantly on the surface of the ZnSe:Mn core, which led to larger d-dots due to a thicker ZnS shell and thus deeper doping of Mn²⁺ in the larger host. Outstanding improvement has been achieved in both phosphorescence intensity and stability after growth of the ZnS shell relative to the ZnSe shell. The corresponding phosphorescence efficiency of the resulting d-dot cyclohexane solution was enhanced from about 8% for the ZnSe:Mn d-dots to 35% for the ZnSe:Mn/ZnS d-dots.