Polymer/silica hybrid waveguide Y-branch power splitter with loss compensation based on NaYF4:Er3+, Yb3+ nanocrystals
Fu Yue-Wu1, Sun Tong-He1, Zhang Mei-Ling2, Zhang Xu-Cheng1, Wang Fei1, †, Zhang Da-Ming1
       

Energy levels of Er3+–Yb3+ co-doped system.