Silica-coupled carbon nanodots: multicolor fluorescence governed by the surface structure for fingerprint recognition and WLED devices

The development of C-Dot-based fluorescent materials with multicolor emissions in the solid state is critical in photoelectric imaging and lighting; however, it is still a challenge to obtain such materials with high optical performances on account of the serious self-quenching generated from the clusters of C-Dots. Here, a one-pot solvothermal method to synthesize S,N-codoped and Si-coupled solid-state carbon nanodot composites (S,N-CNDs/silica) is reported. Leveraging regulating the content of a dopant and the volume ratio of H2O and EtOH solvents, which result in different surface structures of CNDs and CNDs/silica composites during the cross-linked coupling reaction, the PL emissions of the resulting composites shifted from blue to olivine to classify into blue, green, and olivine corresponding to the fluorescence quantum yields (FLQYs) of 10%, 51%, and 9%, respectively. Clearly, the green emitting CNDs/silica composite (G-CNDs/silica) has the highest value, which can be applied to detect latent fingerprints and fabricate LED devices. The result shows that rich details in latent fingerprints can be recognized by the imaging of G-CNDs/silica powder and the WLED device using G-CNDs/silica as a green phosphor to obtain a very high color rendering index (CRI) of 94.2 at a CIE of (0.34, 0.33).