Effects of Li+ Doping Concentration on Structure and Photoluminescence of the Y2O3: Ho3+/Yb3+ Up-conversion Film

The Li+ co-doped Y2O3: Ho3+/Yb3+ films were prepared with sol-gel method and spin-coating technique. The effects of Li+ on the structure and luminescent properties of the films were investigated. The results show the grain size increased first and then decreased with the increase of Li+ doping concentration. The crystal size of particles composing the film got the maximum value when Li+ concentration took 4 mol%. As Li+ doping concentration increased, the optical transmittance of the Y2O3: Ho3+/Yb3+ film improved at first then reduced and got the maximum at 3 mol%. Excited with a 980-nm laser, there were two green emissions in the up-conversion emission spectra, one centered at 535 nm, the other at 550 nm, which ascribed to the 5F4→5I8 and 5S2→5I8 transitions of Ho3+, respectively. The up-conversion luminescence intensity also increased firstly and then decreased with the Li+ doping concentration increase, and got the highest value at 2 mol%.