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

Highlights: • Monodisperse K₃ZrF₇:Yb³⁺/Er³⁺ nanocrystals were synthesized. • Intense red emission upconversion luminescence from Er³⁺ ions was obtained. • Localized Zr cluster structure induced efficient energy transfer from Yb³⁺ to Er³⁺. • The upconversion mechanisms in K₃ZrF₇:Yb³⁺/Er³⁺ were discussed. 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 ⁴S_3/2 and ⁴F_9/2 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.