Thulium concentration quenching in the up-converting α-Tm3+/Yb3+ NaYF4 colloidal nanocrystals

Luminescence spectra, power dependence and luminescence lifetimes were measured and studied in pure cubic phase NaYF4:20%Yb3+, x%Tm3+ (where x = 0.1%, 0.2%, 0.5%, 1% and 2%) nanocolloidal phosphors synthesized by thermal decomposition. Increasing concentration of Tm3+ ions led to decrease of luminescence intensity, increase in the slopes of power dependence as well as to the decrease in the luminescence decay- and rise-times, helping to resolve the mechanisms of up-conversion and concentration quenching.

► Tm3+ ions are highly susceptible to concentration quenching in Tm3+/Yb3+ α-NaYF4.
► Increasing Tm3+ doping decreases the up-conversion intensity by 40, 54 and 4 times at 480, 650 and 800 nm respectively.
► Increasing Tm3+ content promotes the far-red up-conversion emission at 800 nm.
► Luminescence lifetimes of 1G4 level of Tm3+ are bi-exponential above 0.5% of Tm3+ doping and drop from ∼450 μs to 90 μs.
► The order of power dependence for 1G4 and 3H4 levels rises by 10–25% for rising Tm3+ concentration (0.1–2.1%).