Built-in Electric-Field-Induced Electrophotochromism in NaNbO ₃ :Pr ³⁺ Ceramics toward Dual-Mode Time–Temperature Sensing

Chromogenic materials that can reversibly change their body color in response to external stimuli are attracting intense interest for advanced sensing, smart buildings, and optical information storage. Photochromic materials are one of the most important chromogenic materials, but their application is greatly limited by an insufficient color-changing rate and unclear mechanism. Herein, we report an electrophotochromic effect in NaNbO 3:Pr 3+ ceramics, which can synergize the electric-field-driven and light-induced structural changes in the same material to yield more stable color changes. This synergistic mechanism resulted in an ∼87% enhancement in the maximum reflectance difference (Δ R ) at 542 nm, compared with photochromism alone. Systematic studies indicate that the electrophotochromism arises from polarization-driven migration and surface accumulation of charge carriers, along with the resulting built-in electric field. Due to the excellent chromogenic responsiveness to light, electricity, and heat, we demonstrate applications of the NaNbO 3:Pr 3+ ceramics in temperature–time indicators, showing the advantages of integration between real-time visual and delayed quantitative sensing. This work not only reveals the physical mechanism underlying color-changing behavior but also provides a new approach for designing stimulus-responsive materials.