The photo-switch effect and the energy-level population change of Li+ doping in Yb3+/Er3+ co-doped Y2O3 upconversion films

• DOI: 10.1007/s00339-018-2371-1
• Publication Date: 2019-01-12T11:52:57Z
• Authors: Boxu Xu; Juncheng Liu; Kaishun Zou
• Keywords: Photon Upconversion

Li+–Er3+/Yb3+ co-doped Y2O3 upconversion films were prepared via a sol–gel method and spin coating. Li+ doping resulted in better crystallinity and larger crystal grains. All the films had purple, green and red upconversion emission bands. Li+ doping decreased the lattice symmetry of the matrix and enhanced energy transfer, and green and red emissions improved by more than 100 times. Meanwhile, Li+ doping also increased the lifetime of both the green and red emissions significantly via reducing the probability of non-radiation transition. Moreover, the 4S3/2 energy level tends to be populated with increasing Li+, the matrix phonon energy change and the fluorescence quenching causing it. When the mole ratio of rare earth ions to Li+ was over 1:2, the purple emission shifted from 436 to 409 nm. Here, Li+ played a switching role in the conversion of these two channels. Li+ doping up to a critical concentration value changed the matrix phonon energy. The match of the phonon energy with the energy gap between 2G7/2–2H9/2 and that of 2G7/2–4F3/2 was the reason.