Solid-state carbon dots with orange phosphorescence and tunable fluorescence via in-situ growth in phthalimide crystal matrix

Solid-state fluorescent and phosphorescent carbon dots (CDs) have widespread applications, with difficulties in obtainment. In this study, solid-state carbon dots (SCDs) emitting green, yellow, and orange fluorescence were fabricated using urea and phthalic acid as precursors. The band gap size was systematically controlled by varying the ratio of raw material nitrogen. By changing the temperature during synthesis, the phosphorescent properties of SCDs were adjusted, and the longest lifetime possessed 156.8 ms of orange phosphorescence. CDs were attached to the crystals of phthalimide, allowing a certain spacing between the particles and suppressing the phenomenon of aggregation-induced quenching (ACQ), thus obtaining solid-state fluorescence. Detailed characterization and density flooding theory (DFT) calculations further indicate that the reduction of the conjugation domain leads to the redshift of the solid-state fluorescence. The phosphorescence appearance is attributed to the presence of crystals that inhibit the nonradiative relaxation channels, and N elements that promote spin-orbit coupling interactions. Based on their special luminescent properties, they have been successfully applied in the fabrication of (0.38,0.54), (0.44,0.54) and (0.51, 0.47) light-emitting diodes, as well as in the production of secure anti-counterfeit cryptographic inks and their successful application in digital encryption.