Phosphor doped carbon dots with high photoluminescence and stability towards pH and Cr(VI) sensors

To improve the photoluminescence (PL) and increase photostability of carbon dots (CDs), phosphorus doped CDs with bright green emitting were prepared using (NH 4 ) 2 HPO 4 and m-phenylenediamine (MPD), and terephthalic acid (TA) via a solvothermal synthesis. Compared to undoped CDs (M−CDs), the PL efficiency of P-doped sample (M−6 %P-CDs) created using optimized conditions was improved from 55.1 to 73.9 %. These bright CDs were incorporated in films to test the stability, in which the photostability in liquid and polymer films were improved by 6 and 37 %, respectively. Namely, it is found that P affected the functional groups of on the surface and inside CDs. Phosphorus promoted the dehydration condensation reaction of precursors, increased the structural defects of the CDs, separated the sp 2 structural domains, and retained more oxygen-containing functional groups. In the case of o-phenylenediamine (OPD) instead of MPD, the PL efficiency of P-doped CDs was decreased. This is ascribed to P impeding the polymerization process of OPD. These CDs were used for pH and Cr(VI) ion sensors. P-doping improved the sensitivity of CDs to pH and Cr(VI). The pKa value of sample M−6 %P-CDs was 8.32 which was much lower compared with undoped one (∼1.97). Moreover, P-doped CDs revealed significantly enhanced sensitivity response to Cr(VI). The detection range and detection limit of M−6 %P-CDs for Cr(VI) was 1–130 μM and 0.59 μM, respectively. These results are crucial for the preparation and applications of CDs.