Efficient energy transfer in monodisperse Eu-doped ZnO nanocrystals synthesized from metal acetylacetonates in high-boiling solvents

Monodisperse ZnO:Eu nanocrystals were prepared by the codecomposition of metal acetylacetonate precursors in a mixture of oleylamine and I-octadecene. They have been systematically characterized by means of X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectrometry, Raman spectroscopy, and photoluminescence spectroscopy. The as-obtained ZnO:Eu nanocrystals are mainly composed of nanopyramids and dot-shaped nanocrystals and have an average size in the range of 16-32 nm. The valence states of europium ions in the nanocrystals are determined as predominately +3. With increasing dopant concentration of Eu3+ ions, Eu2O3 species tend to segregate on the surfaces of nanocrystals. Under a typical band-edge excitation of ZnO (380 nm), a direct energy transfer from ZnO host to Eu3+ ions, together with a distinct quenching of broad defect emission of ZnO, was observed for the as-obtained doped nanocrystals.