Comparative photoluminescence study of nitrogen-doped carbon dots co-doped with boron and sulphur

Although different studies in carbon dots (CDs) have been reported based on heteroatom doping, most of them have focussed on the enhancement of fluorescence properties. Here we report a comparative study of both fluorescence and room-temperature phosphorescence (RTP) of nitrogen-sulphur-doped CDs (N-S CDs) and nitrogen-boron-doped CDs (N-B CDs) with N-doped CDs (N CDs). The CDs used in the study were synthesized through microwave-assisted pyrolysis. Among the doped CDs, sulphur-doped CDs showed a high fluorescence quantum yield. Upon irradiation, the aqueous dispersion of the CDs demonstrated blue fluorescence. Furthermore, by incorporating the CDs in a potash alum matrix, blue fluorescence, as well as green phosphorescence was observed. The phosphorescence lifetime measurements indicated that the N-S CDs exhibited a longer emission lifetime and a red-shifted emission in contrast with other samples, which might be attributed to the presence of a greater proportion of surface states on the N-S CDs.