Developing Luminescent Ratiometric Thermometers Based on Dual-Emission of NaMgF3:Eu3+/Carbon Dot Nanocomposites

In recent years, the pursuit of luminescent thermometer probes with low cost and high sensitivity has become a significant research challenge. This work proposes a strategy that employs lanthanide ions and carbon dots with dual-emission with diverse temperature dependencies to achieve high-temperature sensitivity. Specifically, the fabrication of dual-activated temperature probes has been achieved using NaMgF₃:Eu³⁺/carbon dot nanocomposites through a simple coprecipitation process at room temperature. The optical temperature sensor, NaMgF₃:Eu³⁺/carbon dot, was developed using Eu³⁺ emission as an internal standard and carbon dot as the temperature signal. The sensor exhibits a substantial absolute sensitivity of 8.3 ± 0.2%K^–1 and a relative sensitivity of 2.0 ± 0.1%K^–1, both at 300 K, making it a promising candidate for physiological thermometry. Within the temperature range of 300–440 K, the NaMgF₃:Eu³⁺/carbon dot probe shows a relative sensitivity of better than 1.0%K^–1 with good excellent repeatability as well as a nearly linear relationship between the Commission Internationale de l’Echlairage chromaticity coordinates of the observed fluorescent color change. The feasibility of the proposed strategy has also been verified by modifying lanthanide ions, e.g., Tb³⁺. It is anticipated that this pilot study will serve as a springboard for research on dual-mode nanothermometers with superior ratiometric and colorimetric performance.