Phosphine-free synthesis of high quality ZnSe, ZnSe/ZnS, and Cu-, Mn-doped ZnSe nanocrystals

High quality zinc blende ZnSe and ZnSe/ZnS core/shell nanocrystals have been synthesized by two converse injection methods (i.e. zinc precursor injection or selenium precursor injection) when Se-ODE complex was chosen as the phosphine-free selenium precursor. Absorption spectroscopy, fluorescence spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to characterize the as-synthesized ZnSe and ZnSe/ZnS nanocrystals. The quality of the as-prepared ZnSe nanocrystals reached the same high level compared with the method using phosphine selenium precursors since the quantum yields were between 40 and 60% and photoluminescence (PL) full width at half-maximum (FWHM) was well controlled between 14 and 17 nm. The parameter window for the growth of high quality ZnSe nanocrystals was found to be much broader and monodisperse ZnSe nanocrystals were synthesized successfully even when the reaction temperature was set as low as 240 degrees C. As cores, such zinc blende ZnSe nanocrystals were also used to synthesize ZnSe/ZnS core/shell nanocrystals with high fluorescence quantum yields of 70%. Cu2+ or Mn2+ doped ZnSe nanocrystals were also synthesized by simply modifying this phosphine-free method. The emission range has been extended to 500 and 600 nm with the use of Cu2+ and Mn2+ dopants compared with the emission coverage of ZnSe at around 400 nm. This is the first totally "green approach" (i.e. phosphine-free synthesis) for the synthesis of high quality ZnSe, ZnSe/ZnS, and Cu2+ or Mn2+ doped ZnSe nanocrystals.