Synthesis of High Temperature-sensitive Properties NaYbF4:Er3+ up-conversion Nanoparticles

Temperature sensing is essential in scientific research, industrial production, healthcare, and daily life. However, conventional thermometers face significant limitations in various situations, such as measuring micro/nano-sized objects, fast-moving targets, corrosive environments, biological tissues, and harsh or hazardous conditions. Fortunately, up-conversion nanoparticles (UNCPs) with unique optical and temperature-sensitive properties have been used as nanothermometers to measure cell temperatures, allowing accurate and sensitive temperature sensing of cells both in vitro and in vivo. UCNPs utilizing thermally coupled energy level fluorescence intensity ratio (FIR) technology have been extensively studied in recent decades due to their advantages in high-precision, non-contact thermal measurements. However, their up-conversion properties are generally constrained by thermal quenching effects, which limit the usable temperature range, measurement accuracy, and resolution, thereby hindering their broader application in temperature sensing. In this study, highly activator-doped core-shell UCNPs can be successfully synthesized based on thermal decomposition method. Relative to core NaYbF4:Er3+ nanoparticles, the up-conversion luminescence of the highly activator doped core-shell UCNPs was enhanced by 24 times and 4 times at 654 nm (red) and 540 nm (green), respectively. The results demonstrated that UCNPs exhibited excellent thermal and repetition stability across a temperature range of 100 K–500 K, with a maximum relative sensitivity (SR) of 11.3% K-1 at 100 K and a minimum temperature resolution (δT) of 0.044 K. These findings highlight the significant potential of this class of fluorescent materials for enhancing temperature-sensitive properties, particularly for optical temperature measurement applications in both low-temperature and wide temperature range environments.