Upconversion Emission Enhancement in Yb³⁺/Er³⁺-Codoped Y₂O₃ Nanocrystals by Tridoping with Li⁺ Ions

Abstract

We demonstrate that tridoping with Li+ ions enhances the visible green and red upconversion (UC) emissions in Er3+/Yb3+-codoped Y2O3 nanocrystals by up to half of the bulk counterpart, i.e., about 2 orders of magnitude higher than previous results. X-ray diffraction and decay time investigations give evidence that tridoping with Li+ ions can tailor the local crystal field of the Y2O3 host lattice. Theoretical calculations illustrate well that a significant UC intensity enhancement arises from the synthesized tailoring effect induced by the Li+ ions, which increase lifetimes in the intermediate 4I11/2 (Er) and 2F5/2 (Yb) states, increase optically active sites in the Y2O3 host lattice, and dissociate the Yb3+ and Er3+ ion clusters in the nanocrytals. The general theoretical description of the visible UC radiations shows that the Yb3+ ion sensitization and the tailoring effect induced by the Li+ ions are two independent enhancement mechanisms, which is expected to lead to an increasing number of photonic and biomedical applications in the future.