Breakthrough Boost of Stokes Fluorescence from Er³⁺ in Perovskites for Flexible Temperature Sensing

Perovskites with ultra‐low phonon energy have excellent radiation properties, while the population distribution of its luminescent initial state needs to be facilitated to further optimize the stokes fluorescence of Er 3+ under high‐energy photons excitation. Herein, UV excitability of Er 3+ is remodeled by building an energy transfer channel from Sb 3+ to Er 3+ in Cs 2 NaInCl 6 (CNIC) microcrystal to realize the enhancement of stokes fluorescence of Er 3+ . Under UV excitation, the breakthrough boost of Er 3+ is observed in Cs 2 NaInCl 6 :Sb 3+ ‐Er 3+ (CNIC:Sb‐Er), and the sensitization coefficient from Sb 3+ to Er 3+ in CNIC is derived to be as high as 112. Moreover, CNIC:Sb‐Er is embedded into functional fibers to enhance the crystal stability and the composite flexibility, which form fluorescence fibers with strong radiation transition probability. Finally, a high‐precision temperature sensing is achieved based on FIR (fluorescence intensity ratios) technology, and the maximum relative sensitivities of CNIC:Sb‐Er phosphors and CNIC:Sb‐Er/PAN fibers reach 1.13 and 1.10% K −1 , respectively, indicating that CNIC:Sb‐Er and CNIC:Sb‐Er/PAN fibers have potential applications in optical temperature sensors.