Thermal Managementof Anti-Stokes Photoluminescenceof Near-Infrared Dyes Using MXene Nanosheets: Implications for PassiveHeating at the Nanoscale

MXene coatings with low thermal emissivity serve as emergent, highly efficient passive heating materials. However, passive heating is usually observed and explored at the macroscale using the micrometer-thick MXene films, whereas application of this phenomenon at the nano- and molecular scale remains unexplored. Here, we use the thermally sensitive, hot-band absorption (HBA) assisted anti-Stokes photoluminescence (ASPL) phenomenon of specific near-infrared dyes as a probe to investigate passive heating of diluted MXene dispersions at the nano- and molecular scale. Diverse thermal emissivities influence the electron activation in the hot band of these dyes differently, leading to changes in the dynamics of ASPL whose intensity increases with increasing temperature. We found that while Nb₄C₃T_<i>x</i> MXene, with relatively high thermal emissivity, renders little interference to the ASPL thermal activation energy, Ti₃C₂T_<i>x</i> MXene, with low thermal emissivity, leads to increasing activation energy, associated with the passive heating effect. The latter process was observed at an MXene concentration as low as 0.01 mg/mL, and it becomes more significant at higher concentration values, for which an increase of the activation energy by a factor of 2 was observed upon increasing Ti₃C₂T_<i>x</i> concentration by an order of magnitude. Our findings indicate that MXene nanosheets can act as the nano/molecular scale heaters and be applied for localized thermal management of quantum processes at the nano- and molecular scale to control HBA-assisted light upconversion, where meticulous fine-tuning of the efficiency is needed.