Defect‐Driven Photochromism for Enhanced Luminescent Thermometry: Mechanisms and Applications in Laser Power Detection

To address the urgent demand for high‐performance luminescent thermometry and overcome the inherent limitations of conventional lanthanide ion‐based thermometric systems, this study proposes a universal strategy for photochromism (PC)‐mediated luminescent thermometry, which is realized by tailoring the electronic interactions between lanthanide ions (Ln 3+ ) and color centers within the host matrix. As a proof of concept, we fabricate a novel PC ceramic, Sr 2 NaNb 5 O 15 doped with Yb 3+ and Er 3+ (denoted as Sr 2 NaNb 5 O 15 : Yb 3+ , Er 3+ ), which exhibits a high PC contrast of ∼42%, fast PC response (< 1 s), and excellent cyclic reversibility. We further reveal that PC‐generated color centers in the Sr 2 NaNb 5 O 15 matrix exert differential modulation effects on the non‐thermally coupled energy level (NTCL) pairs of Er 3+ upon temperature variation. Benefiting from the PC reaction, the maximum absolute and relative sensitivities are enhanced to 23.0 × 10 −3 K −1 and 0.90% K −1 , respectively. Mechanistically, the core of this universal strategy lies in harnessing the pronounced thermal sensitivity of Ln 3+– color center electronic interactions, which are governed by defect‐mediated electron trapping/detrapping processes. We further extend the applicability of this PC‐regulated thermometric strategy to laser power measurement, a previously unreported application scenario that broadens the functional repertoire of PC‐active materials.