Tuning the photothermal effect of NaYF4: Yb3+, Er3+ upconversion luminescent crystals through La3+ ion doping

Bifunctional NaYF4 microcrystals doped with Yb3+/Er3+/La3+ have been successfully synthesized through a facile hydrothermal method, which have been characterized by XRD, SEM, photoluminescence spectra, and the photothermal effect measurement. Under the excitation of 980 nm infrared light, NaYF4: Yb3+/Er3+/La3+ microcrystals can emit green light of 520 nm and 540 nm, red light of 655 nm and violet light of 407 nm. It is observed that the photothermal efficiencies of NaYF4: Yb3+/Er3+ without La3+ ion doping are much lower than the one doped with La3+ ion. With increasing the concentration of the doped La3+ ions, the photothermal efficiencies of NaYF4:Yb3+/Er3+ are monotonously enhanced. Importantly, the time-resolved temperature curves indicated that the temperature rising rate of NaYF4:Yb3+/Er3+ microcrystals is remarkably enhanced by doping La3+ ion. The enhanced temperature rising rate with increasing the content of La3+ doping ion is beneficial to the photothermal effect applications, such as photothermal therapy since the therapy can be completed in the shorter time.