Fig. 4. Quantitative comparison of luminescence rise and decay times of YbEr and Yb@YbEr samples undergoing UC-LRET.

Luminescence rise and decay times for energy levels. ⁴S_3/2 (525–550 nm) (a–c, e–g) and ⁴F_9/2 (650 nm) (d, h) emission from (open symbol) YbEr core only and (solid symbol) Yb@YbEr core-shell UCNPs respectively, at a rising concentration of Rose Bengal attached to their surface. Various excitation modes were compared: a, e 520 nm 10 ns pulse from OPO laser; b, f 980 nm 10 ns pulse from OPO laser; c, g 980 nm 4 ms pulse from TTL-triggered 10 W CW laser diode. The luminescence rise times (τ_R) (a–d) and averaged decay (τ_D) (e–h) components are shown separately