Multi-function up-conversion luminescent Bi4Ti3O12 nanoparticles sensitized by Nd3+ and Yb3+

Up-conversion nanoparticles (UCNPs) stimulated by near-infrared (NIR) light have received immense interest for their potential applications in many fields. In this work, Nd3+- and Yb3+-sensitized Bi4Ti3O12 (BiTx:Nd3+/Yb3+, 0.005 <= x <= 0.3) UCNPs with thermometric and photo-thermal (PT) functions were successfully synthesized by a convenient co-precipitation approach, and the phase and morphologies were characterized. Under 980 nm excitation, BiTx:Nd3+/Yb3+ UCNPs exhibited remarkable multiple emissions in the region from 450 to 900 nm. The visible and NIR emissions were tightly dependent on the Nd3+ concentration and the strongest NIR emissions were obtained in sample BiT0.3:Nd3+/Yb3+. The possible UC mechanisms and processes were proposed. Furthermore, the capability of the UCNPs as thermometers was probed based on the thermo-responsive fluorescence intensity ratio technique in the temperature range 303-573 K. The maximum sensitivity (S-max) of BiT0.3:Nd3+/Yb3+ was determined to be as high as 0.032 K-1. Meanwhile, PT effect was evaluated by monitoring the variation of surface temperature of the sample as functions of irradiation time and power density. Conspicuous PT effect was confirmed and the maximum temperature induced by laser was about 91 degrees C. These results reveal that BiT0.3:Nd3+/Yb3+ UCNPs has promising potential applications as optical thermometer and heater.