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

ABSTRACT 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.