Graphitic Nitrogen and High‐Crystalline Triggered Strong Photoluminescence and Room‐Temperature Ferromagnetism in Carbonized Polymer Dots

Carbonized polymer dots (CPDs) have great potential for bioimaging and biosensing owing to their low toxicity, low cost, resistance to photobleaching, and low environmental impact. Here, the hydrothermal condensation of biomolecules (l‐serine and l‐tryptophan) is used to vary the CPDs' inner structure from amorphous to lattice. A new type of carbon lattice CPD is thus demonstrated that is bright (the photoluminescence quantum yield (PLQY) is as high as 89.57%) and shows room‐temperature ferromagnetism (RTFM), with the magnetic moment increasing from 0.0025 emu g(−1) in crosslinked polymer clusters to 0.021 emu g(−1) in the latticed sample. Hydrothermal synthesis at 300 °C leads to a distinct type of CPD with an obvious carbon lattice, which shows the highest PLQY and the greatest ferromagnetism. Then, the origin of the RTFM is examined in the CPDs via first‐principles calculation, revealing that graphitic nitrogen triggers RTFM in CPDs. Moreover, a possible growth mechanism is suggested that includes kinetics as an important factor in the formation of the CPD crystallites. Overall, these findings identify graphitic nitrogen and high crystallinity as crucial to the enhancement of the CPDs' photoluminescence and room‐temperature ferromagnetism which suggests that they deserve more research attention to develop practical applications.