Sensitization enhancement of europium in ZnSe/ZnS core/shell quantum dots induced by efficient energy transfer.

Eu-doped ZnSe:/ZnS quantum dots (formed as ZnSe:Eu/ZnS QDs) were successfully synthesized by a two-step wet chemical method: nucleation doping and epitaxial shell growing. The sensitization characteristics of Eu-doped ZnSe and ZnSe/ZnS core/shell QD are studied in detail using photoluminescence (PL), PL excitation spectra (PLE) and time-resolved PL spectroscopy. The emission intensity of Eu ions is enhanced and that of ZnSe QDs is decreased, implying that energy was transferred from the excited ZnSe host materials (the donor) to the doped Eu ions (the acceptor). PLE reveals that the ZnSe QDs act as an antenna for the sensitization of Eu ions through an energy transfer process. The dynamics of ZnSe:Eu/ZnS core/shell quantum dots with different shell thicknesses and doping concentrations are studied via PL spectra and fluorescence lifetime spectra. The maximum phosphorescence efficiency is obtained when the doping concentration of Eu is approximately 6% and the sample showed strong white light under ultraviolet lamp illumination. By surface modification with ZnS shell layer, the intensity of Eu-related PL emission is increased approximately three times compared with that of pure ZnSe:Eu QDs. The emission intensity and wavelength of ZnSe:Eu/ZnS core/shell quantum dots can be modulated by different shell thickness and doping concentration. The results provide a valuable insight into the doping control for practical applications in laser, light-emitting diodes and in the field of biotechnology.