Bidirectional Lifetime Tuning of Er 1530 nm Emission Induced by Yb

Wide-range NIR lifetimes of lanthanide ion-doped nanocrystals are highly desired for numerous bioapplications. As one of the most promising NIR emission bands, the lifetime of Er³⁺ at 1.5 μm can be as long as ∼10 ms and be greatly shortened by increasing the doping level of either activator Er³⁺ or sensitizer Yb³⁺. However, the shortened lifetime is mostly accompanied by the quenching effects, highly restraining the light signal intensity. Alternatively, prolonging the lifetime of Er³⁺ NIR lifetime without luminescence quenching is of vital significance as it raises the upper limit of the lifetime range and maintains the effective signal intensity. In this work, we revealed that Yb³⁺ can bidirectionally tune the NIR lifetime of Er³⁺. By introducing Yb³⁺, in addition to the substantially improved luminescence intensities, the prolonged NIR lifetime can be generated in low-Er³⁺-doped NaYF₄ nanocrystals, while monotonously decreased lifetime appears in Er³⁺ heavily doped nanocrystals. To investigate the mechanisms of this bidirectional lifetime tuning and meanwhile avoid additional structural influences, the size and morphology of nanocrystals with different doping compositions were controlled to be similar. The decay dynamics of Er³⁺ NIR emissions of different nanocrystals were simulated to explain the effects of Yb³⁺. This work provides insights into the manipulation of the NIR lifetime in Er³⁺/Yb³⁺-codoped nanocrystals.