Photoluminescence and ZnO → Eu3+ energy transfer in Eu3+-doped ZnO nanospheres

ZnO and Eu3+ doped ZnO nanospheres were synthesized by a wet-chemical method. Scanning electron microscopy showed that all the samples have a regular spherical shape. 5D1 ? 7F2, 5D0 ? 7F0 and 5D0 ? 7F2 emissions originating from intra-atomic 4f?4f transition of Eu3+ were observed in the photoluminescence (PL) spectra. The PL excitation spectrum showed that two strong absorptions centred around 410 and 455?nm appeared besides a weak absorption at 374?nm and three absorption peaks belonging to Eu3+. According to the results of the Raman scattering spectrum and x-ray photoelectron spectroscopy, the two strong absorptions were attributed to substituted Eu3+ (EuZn) and interstitial zinc (Zni) related defect bands, respectively. Moreover, it showed that Eu3+ ions might locate at different sites in the ZnO nanospheres and that energy transfer occurred from ZnO to Eu3+ ions. A possible energy transfer process was described and a corresponding schematic drawing labelling the energy levels of Eu3+ in the ZnO nanospheres was presented. In addition, a nearly white emission which was visible to the naked eye was achieved by introducing Eu3+ into the ZnO nanospheres and this might be significant for developing white light emitters by chemical methods.