title: 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 460 nm and 520 nm 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> 337 nm (the bandgap energy 3.68 eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365 nm and 410 nm. Compared with ZnS nanophosphors, the 520 nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460 nm and 520 nm 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 520 nm 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 460 nm and 520 nm 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.
authors.affiliation: Department of Materials, Huaibei Normal University, Huaibei, 235000, China.|Key Laboratory of Excited State Physics, Changchun Institute of Physics, Chinese Academy of Sciences, Changchun, 130022, China.
authors.forename: Zhang
authors.initials: Z
authors.lastname: Xiao-Bo
authors.affiliation: School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou, 221116, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Fu-Xiang
mesh_terms: D005063:Europium / Q000737:chemistry*; D049449:Luminescence; D054118:Nanospheres; D013440:Sulfides / Q000737:chemistry*; D014961:X-Ray Diffraction; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D013440:Sulfides; D017967:Zinc Compounds; D005063:Europium; C031238:zinc sulfide
keywords: Eu2+ acceptor-bound exciton; ZnS nanophosphor; defect luminescence; electronic relaxation; the intermediate state