Core–Shell NaYF<sub>4</sub>:Yb<sup>3+</sup>/Tm<sup>3+</sup>@NaGdF<sub>4</sub>:Ce<sup>3+</sup>/Eu<sup>3+</sup> Nanoparticles for Upconversion and Downconversion Dual-Mode Fluorescence-Based Temperature Sensing
Mingzhou Meng, Rui Zhang, Xinmeng Fa, Jianghua Yang, Zhenlong Cheng, Xin Qiao, Jun Ou, Christian Würth, Ute Resch‐Genger
Abstract
NaYF4 as the core and NaGdF4 as the outer layer were used to obtain NaYF4:Yb3+/Tm3+@NaYF4:Ce3+/Eu3+ nanoparticles. Physical and morphological investigations indicated that the obtained nanoparticles were prepared in a hexagonal shape, with the NaGdF4 shell layer uniformly encapsulated on the NaYF4 core. Strong Tm3+ upconversion emission peaks were observed for a 980-nm-laser-excited sample, while strong Eu3+ downconversion emission peaks were observed for a 254-nm-laser-excited sample. By zonal doping of Tm3+ and Eu3+, their fluorescence intensity can be significantly increased; more importantly, simultaneous temperature measurements with dual-mode upconversion/downconversion can be achieved. The temperature measurement properties of the dual mode were also investigated, and it was discovered that the upconversion 3F3 → 3H6 and 1G4 → 3F4 thermocouple energy levels gave the best temperature measurements with maximum absolute and relative sensitivities of 0.0877 K–1 and 1.95% K–1, respectively, which are better than the current temperature measurement sensitivities of most rare-earth-based materials. This material was prepared as fiber-optic temperature-sensing probes to detect the temperature in the environment in real time and was found to perform excellently for temperature measurement.