Nitrogen and sulphur co-doped carbon quantum dots and their optical power limiting properties

For the sake of good performance in nonlinear optical (NLO) applications, two S,N-codoped carbon quantum dots (CQDs) were synthesized from 3,7-dinitro-10H-phenothiazine under different conditions of alkaline solution (D-1 from NaOH, D-2 from ammonia). The synthesized carbon quantum dots D-1 and D-2 are monodisperse with narrow size distribution (average 2.8 and 3.1 nm). These CQDs exhibit strong π-π∗ transition in the UV region and broad intramolecular charge transfer (1ICT) transition absorption bands in the visible region. The PL properties of CQDs are excitation and pH dependent. In addition, the PL intensity of the CQDs remains stable under high ionic strength and 100 W UV light irradiation. Moreover, D-1 and D-2 exhibit delightful NLO response and OPL performance at 532 nm and 1000 nm laser pulses, and the results further elucidate that these CQDs are promising nonlinear optical materials for optical power limiting applications.