Preparation of room-temperature phosphorescence fluorine-nitrogen Co-doped carbon dots with sodium lignosulfonate for information encryption and anti-counterfeiting

The key to achieving room-temperature phosphorescence (RTP) is to narrow the energy gap between the first singlet state (S1) and first triplet state (T1) and to stabilize the triplet excited state. In this paper, an environmentally friendly fluorine-nitrogen co-doped carbon dots (FNCDs) were prepared based on sodium lignosulfonate. The films emit stable green phosphorescence at room temperature due to the hydrogen bond formed between carbon dots (CDs) and poly(vinyl alcohol) (PVA), and the heavy-atom effect of fluorine atoms promotes intersystem crossing (ISC). Furthermore, the n-pi* electron transitions of the C--N/C-N bond also promote the green phosphorescence emission of FNCDs@PVA. Compared with single nitrogen-doped carbon dots (NCDs), the steric protection provided by C-F and hydrogen bonds within FNCDs can help the phosphorescence lifetime to reach 494 ms. Based on the properties of FNCDs under different pH, temperature and humidity, we propose several multidimensional advanced information encryption and anti-counterfeiting strategies.