Up-conversion photoluminescence and temperature sensing properties of Er3+-doped Bi4Ti3O12 nanoparticles with good water-resistance performance

Er3+-doped Bi4Ti3O12 (BiT-x) with different particle sizes were successfully synthesized via a low-cost coprecipitation method without any surfactants. The phase and structure were characterized by X-ray diffraction (XRD) and analyzed using Rietveld structural refinements. The morphologies were characterized by scanning electron microscope (SEM). We show that synthesis temperature plays an important role to determine the phase and particle size of BiT-x. As a function of excitation power, it is proved that the obtained BiT-x samples display size-dependent up-conversion (UC) luminescence properties. Meanwhile, with x increase, manipulation of UC emission is observed which can be illustrated by the increased CR process probability. The critical energy transfer distance (R-c) and the major interaction mechanism among Er3+ ions are also determined. Furthermore, the temperature sensing behavior based on fluorescence intensity ratio (FIR) technique from the thermally coupled H-2(11/2) and S-4(3/2) levels are studied in the temperature range from 115 K to 490 K. It is found that the maximum sensing sensitivity is 0.0043 K-1. Meanwhile, BiT-0.05 nanoparticles also display good water-resistance feature. These results reveal that BiT-x oxides may have promising applications in future optical temperature sensors.