Microwave-assisted hydrothermal synthesis of LaOF:Yb3+, Ho3+ nanorods with high thermoresponsive upconversion luminescence for thermometry

Abstract

Non-contact thermometry based on upconversion luminescence from lanthanide-doped nanoparticles is the best choice when temperature probes with higher precision, accuracy, sensitivity, and spatial resolution are required. Here, LaOF:Yb3+,Ho3+ upconversion nanoparticles (UCNPs) were demonstrated to be thermometers with a high sensitivity and thermal stability within the temperature range of 303–673 K. Microwave-assisted hydrothermal synthesis was used to obtain these rod-shaped UCNPs with a trigonal crystal structure. LaOF:Yb3+,Ho3+ UCNPs displayed green emissions due to the thermally-coupled levels (5F4, 5S2) and red emissions from the Stark-split sublevels of the 5F5 energy level belonging to Ho3+ under 980 nm continuous-wave laser irradiation. The upconversion emission originating from these transitions were remarkably sensitive to the temperature variation. Their fluorescence intensity ratios were explored to evaluate their relative (SR) and absolute (SA) sensitivities. Optical heating induced by continuous laser irradiation was also examined to assess the degradation of the luminescence caused by laser exposure.