In this study, new red light-emitting carbon dots (R-CDs) that can selectively recognize Cr(VI) were prepared using a strategy that utilizes 2,4-diaminophenol to enhance the fluorescence of O-phenylenediamine based carbon dots. The results showed that 2,4-diaminophenol increased the quantum yield (QY) of the carbon quantum dots (CDs), and that the QY of the CDs increased from their original value of 8.7% to 20.1% (R-CDs). The R-CDs show sensitivity to acidic conditions and maintain good linearity between pH = 1.00-4.00, making them useful as pH probes. Furthermore, the prepared R-CDs possess good solubility in water and are responsive to changes in Cr(VI) concentrations in aqueous environments. The quenching of the R-CDs fluorescence was linearly correlated with the Cr(VI) concentration within a range of 0-20 μM, with a lower detection limit of 66 nM. The detection mechanism is attributed to the formation of hydrogen bonds between Cr(VI) and the R-CDs, resulting in the fluorescence quenching of the R-CDs. The R-CDs can be considered effective multifunctional fluorescent probes for both pH and Cr(VI) in aqueous environments. This study will provide new R-CD design strategies for probes that selectively identify specific target substances.