Highly Stretchable Eu ³⁺ ‐ Doped PEBAX Elastomers With Complementary Optical Readouts of Strain and Temperature

ABSTRACT

Soft photonic materials capable of maintaining optical functionality under large mechanical deformation are highly desirable for wearable photonics, flexible sensors, optical and mechanically adaptive photonic systems. Here, we report highly stretchable luminescent elastomers based on the thermoplastic copolymer PEBAX 2533 incorporating a europium β‐diketonate complex. The transparent films combine intense europium emission with exceptional mechanical flexibility, displaying elongation at break exceeding 1200%, while maintaining high optical transparency in the visible range. The elastomers exhibit intense red luminescence with absolute quantum yields of 0.61. Under mechanical deformation, the ⁵ D ₀ → ⁷ F ₀ transition shows a strain‐dependent spectral shift and intensity modulation, enabling optical strain readout with sensitivities of –1.6 ± 0.2 cm ⁻¹ ·ε ⁻¹ and −0.44 ± 0.04 ε ⁻¹ , respectively. The luminescence spectra also display a thermal dependence, characterized by a blue shift and intensity decrease of the Eu ³⁺ emission with a temperature sensitivity of 0.08 ± 0.01 cm ⁻¹ ·°C ⁻¹ over the investigated temperature range. The coexistence of large deformability, high transparency, efficient Eu ³⁺ emission, and two independently calibrated optical responses establishes Eu‐doped elastomers as a versatile soft photonic platform for multimodal optical transduction, highlighting their potential for flexible sensing technologies in which mechanical and thermal perturbations are optically encoded within the same material platform.