High-Gravity-Assisted Intensified Preparation of Er-Doped and Yb/Er-Codoped CaF₂ Upconversion Nanophosphors for Noncontact Temperature Measurement

Abstract

Rare earth ion doped upconverison (UC) luminescence nanophosphors have attracted much attention owing to their wide applications. It is known that homogeneous doping of ions in matrixes and particle size distribution (PSD) determine the luminescent properties. In this study, we reported a novel approach to prepare CaF2:Er3+ and CaF2:Yb3+/Er3+ UC nanophosphors by high-gravity reactive precipitation in a rotating packed bed (RPB) combining hydrothermal process, which is applied for noninvasive temperature detection. The intensified micromixing in the RPB reactor contributes to the achievement of CaF2 nanoparticles with a narrower PSD, more homogeneous doping of Er3+ and Yb3+ ions in the CaF2 matrix, and higher doping efficiency compared to a conventional stirred tank reactor (STR). In particular, the luminescent intensities of the as-prepared CaF2:Er3+(2%) and CaF2:Yb3+(10%)/Er3+(1%) are respectively 12 and 2 times higher than those of the corresponding products prepared in the STR. Furthermore, the maximum absolute sensitivity of RPB-prepared CaF2:Yb3+(10%)/Er3+(1%) is calculated to be 0.0049 K–1, comparable with those of other reported Yb3+/Er3+-codoped materials. This exhibits a great potential of CaF2:Yb3+/Er3+ UC nanophosphors as promising noncontact temperature measuring materials.