Photoluminescence (PL) is a crucial property of carbon dots (CDs), which are promising carbon nanomaterials for agricultural applications. Red light signaling positively influences various physiological processes in plant salt tolerance. However, the potential for designing CDs based on light signaling theory to enhance agronomic traits in field crops remains unexplored. In this study, foliar spraying of red-emissive CDs (RCDs) improved salt tolerance in sweetpotato (Ipomoea batatas (L.) Lam) by enhancing nitric oxide (NO)-mediated Na⁺ homeostasis in roots. A mechanistic investigation attributed this beneficial effect primarily to the PL properties of the RCDs. The expression of genes related to RCD-enhanced Na⁺ transport in roots was found to be dependent on NO-mediated histone acetylation. For instance, RCDs, including genes encoding the red-light receptor (IbPHYB) and the Na⁺/H⁺ antiporter (IbSOS1), triggered comprehensive histone H4 hyperacetylation in salinized sweetpotato roots. IbHY5 was identified as a potential shoot-to-root mobile signal that triggered the hyperproduction of NO in sweetpotato roots under stress conditions. In summary, the RCDs enhanced salt tolerance in sweetpotato via the IbHY5-NO-IbHAM1-IbSOS1 signaling. These findings revealed that the PL properties of CDs could target specific light signaling pathways for field crop improvement.