Investigation on laser-induced heating in NaYbF4:Er3+ for accurate photo-thermal conversion with temperature feedback

The laser-induced local heating effect under the irradiation of 980 nm near-infrared laser was investigated in NaYbF4:Er3+ with the upconversion emission intensity ratio of Er3+ as a real-time temperature probe. Under the excitation power density of 9.1 W/cm2 the temperature of the irradiated sample can increase from room temperature to about 580 K in 5 s, indicating that NaYbF4:Er3+ could be an efficient heat source for accurate photo-thermal conversion with temperature feedback, which may be applied in photo-thermal therapy, drug release, etc. The result also shows that the dependence of upconversion emission intensity of Er3+ ions on power density of pump laser is time-related, the saturation of upconversion emission is very obvious for steady state irradiation while the saturation is not observed at the beginning of irradiation, implying that the saturation of upconversion emission is mainly caused by the thermal quenching at high temperature induced by laser irradiation with high power density.