Efficient room temperature phosphorescence carbon dots: Information encryption and dual-channel pH sensing

Chemical doping with nitrogen, phosphorus or halogens can effectively favor the room temperature phosphorescence (RTP) appearing of carbon dots (CDs) through facilitating their intersystem crossing (ISC) process. Here we raised a facile microwave strategy to synthesize nitrogen and phosphorus co-doped carbon dots (P-CDs), while triethanolamine served as the carbon source with phosphoric acid being the dopant. Meanwhile, the P-CDs showed both the bright-blue fluorescent emission and the green-RTP emission. Additionally, the filter paper functioned as the matrix to stabilize the triplet excitons of P-CDs, thus achieving their RTP emission by suppressing the non-radiative transitions. Significantly, an innovative painting technology of employing P-CDs as RTP-ink has been developed toward the confidential information encryption. Moreover, we applied the proposed P-CDs to respectively assay pH ranging from 9.15 to 13.55 and 2.29 to 13.55 by virtue of their pH-responsible fluorescence and RTP. Again, we further explored the fluorescent and phosphorescent sensing mechanism of P-CDs by the deprotonation of P–O bonds and the precipitation of P-CDs.