LAUSR

A series of Zn2+ and Li+ inert ion single/co-doped Gd2O3: Ln3+ (Ln = Yb/Er, Eu) nanocrystals (NCs) were synthesized by a simple precipitate method followed by annealing at a high temperature. Compared with undoped Gd2O3: Ln3+ (Ln = Yb/Er, Eu) NCs, the samples doped with Zn2+ or Li+ ion all show an obvious enhancement on their upconversion (UC) and downconversion (DC) luminescence intensity. On the basis of the best single doping concentration of Zn2+ or Li+ ion, we codoped another ion (Li+ or Zn2+) into the NCs; the luminescence intensity shows a further enhancement. As a result, Zn2+ and Li+ dual ion codoping is a better strategy than single doped Zn2+ or Li+ ion to enhance the luminescence properties of Gd2O3: Yb/Er and Gd2O3: Eu NCs. This can be attributed to the smaller radius of the Zn2+/Li+ ions (Zn2+: 0.088 nm, Li+: 0.09 nm, all for six coordination) than that of the radius of Gd3+ ion (Gd3+: 0.1078 nm), and the heterogeneous valence of the Zn2+/Li+ ions. When they occupy the Gd3+ crystal lattice site in Gd2O3 NCs, they play different roles and complement each other in improving luminescence intensity of Gd2O3: Ln3+ (Ln = Yb/Er, Eu) NCs.