Broadband nonlinear optical properties of red fluorescent carbon dots

Carbon dots (CDs) provide ideal platforms for applications in bioimaging, sensing, and photocatalysis. Herein, a new type of red fluorescent carbon dot (RCD) is successfully synthesized, and its broadband nonlinear optical (NLO) properties are systematically characterized. The nonlinear absorption coefficient (αNL) values of the RCDs at 580, 630, 650, 1064 nm are − 0.65, −3.09, −4.02, and 0.14 cm/GW, respectively. The nonlinear absorption transforms from saturable absorption to two-photon absorption in the near-infrared domain. We demonstrate the application of the RCDs for imaging Hela cells. Our results indicate that the synthesized RCDs with a broadband NLO response exhibit potential applications in saturable absorbers and deep-tissue imaging.