Nd3+ doped TiO2 nanocrystals as self-referenced optical nanothermometer operating within the biological windows

Abstract

In this work, we report a potential optical nanothermometer (NTh) based on Nd3+ doped TiO2 nanocrystals, operating within the biological windows. The Nd3+ emissions at around 900, 1060, and 1340 nm were used upon excitation at 808 nm. The fluorescence intensity ratio (FIR) corresponding to the emissions at 1060 nm and 1340 nm (FIR = I1060 nm/I1340 nm) was investigated as a function of the temperature in the range of 300−343 K. In addition, the effect of the Nd3+ ions concentration and influence of the crystalline phase on the luminescence and the relative thermal sensitivity were presented. As a result, it was found that TiO2 nanocrystals doped with 10 wt% of Nd3+ ions and associated with the brookite phase has the highest luminescence emission and relative thermal sensitivity compared to other samples investigated here and in previous literature. The maximum value obtained to the relative thermal sensitivity was 0.86 % K−1, which is high comparatively with other ones of Nd3+ doped systems, and minimum thermal resolution of ∼1 K. This information together with the biocompatibility of TiO2 nanocrystals, and excitation and emissions wavelengths lying within the biological windows, favor potential applications in fluorescence and thermal imaging of biological systems.