Luminescent Pb-free perovskites: low-cytotoxicity materials for primary thermal sensing

Selecting a suitable host matrix to perform temperature sensing in biomedical applications requires low cytotoxicity, facile synthesis, and an ability to be doped with light-emitting ions. With this perspective, indium-based halide double perovskites, specifically Cs 2 AgIn 0.9 Bi 0.1 Cl 6 , Cs 2 Ag 0.6 Na 0.4 InCl 6 , and Cs 2 Ag 0.6 Na 0.4 In 0.9 Bi 0.1 Cl 6 , were chosen as host materials to develop lanthanide-based primary thermometers due to their low phonon energy and ease of synthesis. The incorporation of Na + and Bi 3+ into the perovskite cubic crystal lattice was confirmed by X-ray diffraction and Raman spectroscopy while the optical properties of both the undoped and Yb 3+ /Er 3+ co-doped perovskites were assessed by diffuse reflectance and photoluminescence spectroscopies. The obtained perovskite samples demonstrated excellent thermal stability, with the ability to withstand temperatures as high as 500 °C. A temperature-dependent green emission of Er 3+ was observed in the co-doped samples upon 980 nm irradiation, yielding a relative thermal sensitivity and uncertainty in temperature values of 1.3% K −1 and 0.3 K, respectively. Incorporating the obtained perovskites (0.05 to 0.20 mg mL −1 ) into L2929 cells as an in vitro model resulted in high cell viability, underscoring the benefits of selecting such a low-cytotoxicity material for applications in biological media. Novel luminescent In-based lead-free double halide perovskites co-doped with Yb 3+ /Er 3+ have been synthesized. Their primary thermometer performance was assessed and their biological application to predict temperature was evaluated.