Synthesis and characterization of nanocrystals in the Zn–Se–O system

Abstract

The synthesis of binary ZnSe and ZnO nanocrystals from non-organometallic precursors is described. Crystal growth can be conveniently monitored by UV–vis spectroscopy, showing a continuous red-shift of the excitonic peak with increasing nanocrystal size. X-ray diffraction investigations indicate a wurtzite-type crystal structure for both binary systems. With the goal to prepare ternary ZnSe 1 - x O x nanocrystals, two general methods have been tested. The first method consisted of the doping of already formed ZnO or ZnSe nanocrystals with the missing anion. Attempts of doping of ZnO with Se gave a mixture of wurtzite ZnO and sphalerite ZnSe nanocrystals, whereas the doping of pre-formed ZnSe nanocrystals with O resulted in the transformation of their wurtzite structure into the sphalerite one with no formation of a separate ZnO phase. An alternative approach to the preparation of the ternary ZnSe 1 - x O x compound involved nanocrystals nucleation and growth in the presence of both, ZnSe and ZnO, precursors. This method led to a mixture of wurtzite ZnO and sphalerite ZnSe nanocrystals. It is postulated that the sphalerite structure is stabilized by incorporation of small amounts of O into the ZnSe lattice, which is manifested by a slight modification of the X-ray diffraction profiles and a decrease in the band gap value clearly observed in the UV–vis spectra.