Luminescent PMMA Films and PMMA@SiO2 Nanoparticles with Embedded Ln3+ Complexes for Highly Sensitive Optical Thermometers in the Physiological Temperature Range**

In recent years, luminescent materials doped with Ln3+ ions have attracted much attention for their application as optical thermometers based on both downshifting and upconversion processes. This study presents research done on the development of highly sensitive optical thermometers in the physiological temperature range based on poly(methyl methacrylate) (PMMA) films doped with two series of visible Ln3+ complexes (Ln3+=Tb3+, Eu3+, and Sm3+) and SiO2 nanoparticles (NPs) coated with these PMMA films. The best performing PMMA film doped with Tb3+ and Eu3+ complexes was the PMMA[TbEuL1tppo]1 film (L1=4,4,4-trifluoro-1-phenyl-1,3-butadionate; tppo=triphenylphosphine oxide), which showed good temperature sensing of Sr=4.21 % K−1 at 313 K, whereas for the PMMA films doped with Tb3+ and Sm3+ complexes the best performing was the PMMA[TbSmL2tppo]3 film (L2=4,4,4-trifluoro-1-(4-chlorophenyl)-1,3-butadionate), with Sr=3.64 % K−1 at 313 K. Additionally, SiO2 NPs coated with the best performing films from each of the series of PMMA films (Tb–Eu and Tb–Sm) and their temperature-sensing properties were studied in water, showing excellent performance in the physiological temperature range (PMMA[TbEuL1tppo]1@SiO2: Sr=3.84 % °C at 20 °C; PMMA[TbSmL2tppo]3@SiO2: Sr=3.27 % °C at 20 °C) and the toxicity of these nanoparticles on human cells was studied, showing that they were nontoxic.