Evolution of Er${}^{3+}$/Yb${}^{3+}$-codoped NaGdF${}_4$ nanorods at room temperature for non-contact nanothermometer and optical heater

The homogenous Er${}^{3+}$/Yb${}^{3+}$-codoped NaGdF${}_4$ nanorods were prepared through an ingenious reaction technology at room temperature. The influence of synthetic time on the phase category and microstructure of the studied compounds was examined in detail. When the reaction time was 3 h, the Er${}^{3+}$/Yb${}^{3+}$-codoped NaGdF${}_4$ nanorods with single hexagonal phase were obtained. Upon 980 nm light excitation, visible upconversion emissions were detected in the synthesized nanorods and the involved luminescent mechanism pertained to be a two-photon absorption process. Based on the ${}^2$H${}_{11/2}$ and ${}^4$S${}_{3/2}$ thermally coupled levels, the optical thermometric behaviors of the resultant nanorods were discussed via fluorescence intensity ratio technology and the maximum sensor sensitivity was about 0.0021 K${}^{\text{â}\text{ˆ}\text{’}1}$ at 491 K. Moreover, we also dealt with the laser-induced optical heating properties of the Er${}^{3+}$/Yb${}^{3+}$-codoped NaGdF${}_4$ nanorods and the temperature of the final product was boosted to 348 K when the excitation pump power was 260 mW. These achievements imply that the bifunctional Er${}^{3+}$/Yb${}^{3+}$-codoped NaGdF${}_4$ nanorods are a promising candidate for simultaneous nanothermometer and optical heater.