Modulation of the up-converting optical properties of Yb3+/Tm3+ doped α-NaYF4 nanocrystals with calcium co-doping

To increase luminescence efficiency, the substitution of matrix ions with ion of alternative size and valence has been used to create lattice distortions and disrupt the processes responsible for luminescence quenching. Therefore, luminescent properties of cubic NaYF4:Yb3+/Tm3+ nanocrystals co-doped with Ca2+ ions have been studied. The general increase in the luminescence intensity as well as in thulium excited states lifetimes have been observed upon Ca2+ doping. The optimal calcium ions concentration has been found equal to 5% in the case of samples doped with 0.1% Tm3+. The most efficient UC luminescence in the case of 2% Tm3+ doped samples has been observed for 10% Ca2+ doped sample. Additionally, the impact of intentional substitution of either Na+ or Y3+ ions by Ca2+ ions in NaYF4 matrix has been compared. Similar modulation effects have been observed for both doping methods.