Eu2+ -induced enhancement of defect luminescence of ZnS.

Abstract

The Eu2+ -induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460nm and 520nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λex >337nm (the bandgap energy 3.68eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365nm and 410nm. Compared with ZnS nanophosphors, the 520nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460nm and 520nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu2+ intra-ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu2+ acceptor-bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non-radiative electronic relaxation and thus increases the intensity of the 460nm and 520nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu2+ -doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.