Enhancement of the upconversion photoluminescence intensity in Li⁺ and Er³⁺ codoped Y₂O₃ nanocrystals

Infrared-to-visible upconversion luminescence spectra are investigated in Li⁺ and Er³⁺ codoped Y₂O₃ nanocrystals. By introducing Li⁺ ions, the upconverted emission intensity is found to be greatly enhanced when compared with the nanocrystals with the Li⁺ absent. The cause of the enhancement is believed to be the modification of the local symmetry of the Er³⁺ ion, which increases the intra-4f transitions of Er³⁺ ion, and the homogeneous distribution of Er³⁺. While in some other Er³⁺ doped oxides, such as ZnO, ZrO₂, etc., the upconversion intensity of Er³⁺ ions could also be greatly increased by doping Li⁺.