Localization induced intense red upconversion luminescence in monodispersed K3ZrF7:Yb3+/Er3+ nanocrystals

There are increasing demands for upconversion (UC) nanocrystals since they are found to have important applications in the field of bio-imaging. Herein, novel monodispersed Yb3+/Er3+ co-doped K3ZrF7 nanocrystals with tunable sizes of 6–30 nm were prepared by high temperature co-precipitation method. Intense UC emission of Er3+ with large red to green ratio was obtained under the excitation of 980 nm-laser due to the cation localization effects. The UC luminescent lifetimes of 4S3/2 and 4F9/2 were determined to be 0.137 and 0.217 ms, respectively. At last, the possible upconversion mechanism was proposed basing on the pump power dependent UC luminescence experiments.