Sulfur doping pyrene-based carbon dots with multicolor room temperature phosphorescence for information encryption

The growing demands for multiple-level optical information encryption require the development of novel room temperature phosphorescence (RTP) materials with long afterglow performance and multi-color phosphorescence. Carbon dots (CDs), as a new generation of carbon-based luminescent nanomaterials, have received widespread attention. Here, a series of sulfur-doped carbon dots (S-CDs) with different sulfur doping regulation are proposed as emitters to fabricate RTP materials by embedding boric acid (BA) matrix. With different sulfur doping amount, S-CDs exhibit green, yellow-green and orange RTP, respectively. The RTP spectrum can be split into three emission centers with different intensities. Thus, the multi-color RTP emission is ascribed to varied surface state of S-CDs involving the phosphorescence center intensity changes, which results from sulfur doping. The RTP lifetimes of these S-CDs are calculated to be 579.28, 540.87, and 288.89 ms, which is measured for S-CDs-G@BA, S-CDs-Y@BA and S-CDs-O@BA, respectively. In addition, the phosphorescence quantum yield (PQY) is 27.93 %, 10.62 % and 13.58 %, respectively. The encryption test is performed utilizing these multi-color RTP S-CDs, demonstrating that these S-CDs have good RTP performance and are suitable for anti-counterfeiting and information encryption.