Figure 5.

Decay curves of Ho³⁺. For (a) ⁵ F₃ → ⁵I₈, (b) ⁵ F₄, ⁵S₂ → ⁵I₈, and (c) ⁵ F₅ → ⁵I₈ emissions under excitation of 450 nm. The inset shows the average decay lifetime and energy transfer efficiency as a function of Yb³⁺ doping concentration. (d) Energy level diagram of Ho³⁺ and Yb³⁺ showing mechanisms for NIR QC processes.