Dual photoluminescence centers from inorganic-salt-functionalized carbon dots for ratiometric pH sensing

A controlled and effective strategy for synthesizing carbon dots (CDs) with dual photoluminescence (PL) peaks is presented in this report which involved employing coal-based CDs as seeds, and using appropriate diammonium phosphate (DAP) as a modifying agent. The formation of dual PL color CDs (D-CDs) mainly depends on the reaction temperature and thermally induced surface remodification of coal-based CDs with DAP. The origin of dual PL peak emissions is attributed to the presence of grafted N- and P-related groups on CDs through DAP functionalization. The synthesized D-CDs show a distinct pH-sensitive behavior under optimized laboratory conditions. Accordingly, a fluorescent ratiometric probe is developed based on these CDs for the detection of pH distribution and variation over a broad range in a complex system with interferingmetal ions.