Extended Data Fig. 6: In-depth study of photodarkening of 176-nm NaLuF4:Tm(15%) nanodiscs.
From: Optical nonlinearities in excess of 500 through sublattice reconstruction
a, Increasing and decreasing excitation power scans for 176-nm NaLuF4:Tm(15%) nanodiscs over a wide power range. The inset shows an enlarged view of the pre-photon avalanche (PA) and PA regions, with the excitation power around 107 kW/cm² highlighted. This range is particularly sensitive for probing the occurrence of photodarkening. b, Experiment to quantitatively determine the photodarkening threshold. Initially, five cycles between 106.2 kW/cm² and 110.6 kW/cm² were conducted to confirm that changes in power density below the photodarkening threshold would not lead to irreversible changes in luminescence intensity. Subsequently, the low-power level was maintained at 106.2 kW/cm², while the high-power level was gradually increased from 108.2 kW/cm² to 373.5 kW/cm². After each power adjustment, a 10-second stabilization period was allowed to measure the luminescence intensity.
