Layer-by-Layer Assembly of Carbon Dots-Based Ultrathin Films with Enhanced Quantum Yield and Temperature Sensing Performance

Carbon dots (CDs), an rising kind of fluorescent carbon material, have been extensively studied due to their unique physicochemical properties, but the research on solid state devices and applications is rather lacking. Herein, we report the fabrication of fluorescent ultrathin films (UTFs) by embedding CDs into the 2D layered double hydroxides (LDHs) nanosheets through layer-by-layer assembly. The resulting UTFs present long-range ordered structure and improved luminescent properties compared with the CDs drop-casted films, including quantum yield (57.17% vs 3.04%) and fluorescence lifetime (14.47 ns vs 0.813 ns). This significant enhancement is due to the molecular level dispersion of CDs and the confinement of photoexcited electrons imposed by LDH nanosheets, which is confirmed by both experimental studies and density functional theoretical (DFT) calculations. Moreover, the UTFs display temperature-responsive photoluminescence (PL) and electrochemiluminescence (ECL) performances. Therefore, this work provides a facile method for the design and fabrication of CD UTFs with excellent luminescent properties, which can be potentially used in optical/optoelectronic sensing devices.