Chiral carbon quantum dots for optical power limiting application

In this research, the introduction of chirality into carbon quantum dots (CQDs) successfully facilitated the formation of chiral carbon quantum dots (CCQDs). These CCQDs manifested excellent photophysical properties. Moreover, chirality was exploited as a key factor to modulate the optical power limiting (OPL) properties of the CQDs. Chiral activities of precursors l/d-threonine (Thr) and l/d-cysteine (Cys) were used to prepare l/d-ThrCQD and l/d-CysCQD, respectively. The OPL performance of l/d-CysCQD was better than that of l/d-ThrCQD, because the band gap of l/d-CysCQD, containing N and S elements, was smaller than that of l/d-ThrCQD doped with N atoms. The carbon core formed by combining N and S atoms with sp2 hybridized carbon had a structure similar to D–π–A. This enhanced the electron transport ability, reduced the band gap, and improved the OPL performance. Additionally, the Z-scan test results showed a difference in OPL between the l- and d-types, with d-type CCQDs having higher nonlinear absorption coefficients than l-type CCQDs. To investigate this phenomenon, the band gaps were calculated, and it was determined that the d-type band gap was smaller than that of the l-type. This affected the former’s electron transfer and improved its OPL performance. This result provides new avenues for the practical application of CQD chiral modulation in the field of OPL.