Mechanisms of Upconversion Luminescence of Er-Doped NaYF via 980 and 1530 nm Excitation.

To date, the mechanisms of Er upconversion luminescence via 980 and 1530 nm excitation have been extensively investigated; however, based on discussions, they either suffer from the lack of convincing evidence or require elaborated and time-consuming numerical simulations. In this work, the steady-state and time-resolved upconversion luminescence data of Er-doped NaYF were measured; we therefore investigated the upconversion mechanisms of Er on the basis of the spectroscopic observations and the simplified rate equation modeling. This work provides a relatively simple strategy to reveal the UCL mechanisms of Er upon excitation with various wavelengths, which may also be used in other lanthanide ion-doped systems.