White-light upconversion emission of lanthanide double-doped oxide nanoparticles via defect state luminescence of ZnO

Abstract

The white upconversion luminescence (UCL) of upconversion nanoparticles (UCNPs) is mainly made up of the color red, green and blue. Interestingly, the white-light-emitting UCNPs can be obtained via a complex method of tridoping lanthanide ions such as Yb3+, Er3+, and Tm3+. We herein report that an excellent white UCL can be obtained from Yb/Tm double-doped ZnO. In this system, the blue and red UCL-emissions around 475 and 652 nm originate from 1G4→3H6 and 1G4→3F4 transition of Tm3+, respectively, and the green one can be attributed to the defect states (oxygen vacancies) luminescence (DSL) of the ZnO host. Meanwhile, the fine nanostructure of ZnO:Yb/Tm is prepared by adjusting the concentration of OH−. Particularly, the one dimentional pencil-shaped nanorods with high aspect ratio achieve a strong green DSL emission due to the high concentration of oxygen vacancy. The oxygen vacancy defects play an irreplaceable role in affecting the intensities of blue and red UCL by acting as the intermediate state in the energy transfer process. More importantly, we demonstrate that the DSL and UCL can be combined into systems, paving a new road for obtaining the white UCL emission.