Unveiling the Excited‐State Dynamics and Interfacial Interactions in Dye‐Sensitized NaNdF4 Nanoparticles for Efficient Photothermal Effect

Abstract Near‐infrared (NIR) dyes can overcome the weak absorption of lanthanide nanoparticles (NPs) by antenna sensitization, offering new avenues to develop efficient and versatile lanthanide nanomaterials. However, current research on dye‐sensitized lanthanide NPs for photothermal conversion is still preliminary, and the involved excited‐state dynamics and interfacial interactions remain elusive. Herein, steady‐state/transient absorption spectroscopy and theoretical calculation are used to investigate the coordination and aggregation states of cypate dyes on NaNdF 4 NPs, revealing the influence of interfacial interactions on resonant energy transfer. Synergetic heat‐generation mechanism of lanthanide cross‐relaxation and dye intermolecular collisions is further proposed. The photothermal conversion efficiency of cypate‐NaNdF 4 nanocomposites reaches 50.4%, outperforming those of typical photothermal materials with high NIR absorption. Moreover, the intersystem crossing of cypate can be inhibited due to the depopulation of the S 1 exciton via ET, thereby improving anti‐photobleaching ability. These dye‐sensitized NaNdF 4 nanocomposites exhibit superior photothermal effect, stability and NIR‐II luminescence, showing great potential in theranostic applications.