Solid-state emission gain of sodium-doped blue photoluminescent carbon dots and its application in temperature sensing

As a new type of zero-dimensional nanoluminescent material, carbon dots (CDs) have attracted extensive attention and in-depth research in recent years due to their rich and excellent luminescence properties. In this study, sodium-doped CDs (Na-CDs) were synthesized under three different sodium source conditions by hydrothermal method, and the regulation mechanism of Na-doped on the structure and optical properties of CDs was systematically studied by comparing with undoped control samples. The results show that Na-doped does not significantly change the particle size and crystal structure of CDs, but can significantly increase the proportion of graphite nitrogen (from 12.3 % to 65.3 %), enhance the order of sp² carbon structure, thereby effectively inhibiting π-π stacking, and significantly improving the fluorescence quenching problem of CDs in the solid state. Among them, the self-doped CDs-1 exhibits strong and stable blue fluorescence in both solution and solid state, with emission peaks at 447 nm and 455 nm, respectively, phosphorescence quantum yields (PLQY) of 22.61 % and 9.02 %, respectively, and an average fluorescence lifetime of 7.75 ns, which is much higher than other samples. Temperature response experiments show that the fluorescence intensity of CDs-1 shows a decay trend with increasing temperature in the range of 80–300 K, and shows a good linear relationship in the range of 160–300 K. The fluorescence intensity decreases by an average of 0.0191 % for every increase of 1 K, showing excellent temperature sensitivity and stability. This study provides new ideas for the design of high-performance solid-state luminescent CDs and expands their application potential in the field of optical functional materials such as non-contact temperature sensing.