THE DOPING OF Eu 2+ -INDUCED ENHANCEMENT IN DEFECT LUMINESCENCE OF ZnS

摘要

The doping of Eu 2+ -induced enhancement in defect luminescence of ZnS (i.e., the 460 nm and 520 nm emission), is studied in this work. While the photoluminescence spectra show the 460 nm and 520 nm emission in both ZnS and ZnS:Eu phosphors, the photoluminescence excitation spectra show different excitation characteristics in the two phosphors. In ZnS phosphors, no excitation absorption signal is observed at the excitation wavelength λ ex ＞ 337 nm (the bandgap energy). In ZnS:Eu phosp hors, however, the 365 nm and 410 nm excitation bands, which correspond respectively to the absorption of Eu 2+ acceptor level and the intra-ion transition absorption of Eu 2+ , appear remarkably. Compared with ZnS phosphors, the 460 nm and 520 nm emissions are increased in intensity b y more than 10 times in ZnS:Eu phosphors and the 520 nm emission is relatively enhanced as well. The reason is analyzed. It's revealed from this work that the doping of Eu 2+ enhances defect luminescence of ZnS from two aspects. First and most important, the excited levels of Eu 2+ acceptor-bound exciton serve as the intermediate state for electron relaxation, which avoids the non-radiative electron transfer to the valence band and thus increases the 460 nm and 520 nm emissions. Second, the intra-io n transition absorption of Eu 2+ and subsequent energy transfer to sulfur vacancy cooperatively lead to the relative enhancement of the 520 nm emission.