All-inorganic lead-free double perovskite Cs2NalnCl6 for fiber-based optical temperature sensing for temperature and safety monitoring

Double halide perovskites are widely utilized in photocatalysis, photovoltaics, and light emission owing to their nontoxicity and chemical stability. Their excellent temperature-dependent optoelectronic properties also provide the potential for temperature sensing. However, most double halide perovskites typically exhibit low photoluminescence quantum yields due to indirect bandgaps and parity-forbidden transitions, limiting their further applications. Here, we report the synthesis of Cs2NaInCl6 double perovskites via the hydrothermal method, introducing Sb3+ to enhance broad blue emission. Additionally, Mn²⁺ co-doping is employed to achieve tunable dual emission, ensuring the phase stability and efficient luminescence output of the Cs2NaInCl6. By testing photoluminescence spectra at a broad working temperature ranging from 300 to 500 K, a visible color change from purple to dark salmon was observed as the temperature increased, resulting in higher absolute and relative temperature sensitivity of 0.008 K-1 and 1.2% K-1, respectively. Furthermore, Cs2NaInCl6:Sb3+-Mn2+ was integrated into the fiber or attached it to the fiber surface. Under varying temperatures, the fiber exhibited a color change, demonstrating that Sb³⁺-Mn²⁺ co-doped Cs₂NaInCl₆ is a promising material for fiber-based optical temperature sensing in temperature and safety monitoring applications.. Notably, the thermal behavior of the sensor enables its application in wearable flexible display, lighting and anti-counterfeiting.