Ultrasensitive Anti‐Stokes Luminescence Thermometry in Transition Metal Dichalcogenide Monolayers

ABSTRACT Accurate temperature mapping at the nanoscale is a critical challenge in modern science and technology, as conventional methods fail at these dimensions. To address this challenge, we demonstrate a highly sensitive nanothermometer using anti‐Stokes photoluminescence, also known as photoluminescence upconversion (UPL), in monolayer tungsten disulfide. Leveraging the direct band gap and strong exciton‐phonon coupling in the monolayers, we achieve an exceptional relative sensitivity above 4% K − 1 across 300 to 425 K, ranking it among the best‐performing materials reported. A strong resonantly enhanced UPL is observed, confirming the central role of optical phonons in the upconversion mechanism. Furthermore, we introduce an analytical model to quantitatively describe the UPL process, taking into account the interplay of phonon populations, bandgap narrowing, and substrate effects, which predicts resonant temperatures and provides a framework with broad applicability to any material exhibiting an anti‐Stokes photoluminescence response. To demonstrate its use as a high‐resolution optical thermometer, we map a 20°C thermal gradient across a 20 µm long monolayer with a spatial resolution of 1 µm. With its high sensitivity, strong signal, and excellent reproducibility, our work establishes monolayer transition metal dichalcogenide as a leading platform for non‐invasive thermal sensing in advanced microelectronic and biological systems.