Role of Core and Surface States Electronic Structure in the Tunable Optical Properties of Nitrogen‐Doped Carbon Dots

This study presents a comprehensive investigation of nitrogen‐doped carbon dots ( N‐ CDs) synthesized using perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA) as the carbon source and urea as the nitrogen dopant. Notably, the N ‐CDs exhibit remarkable preservation of PTCDA‐like characteristics, as evidenced by a distinctive photoluminescence (PL) profile with multiple well‐defined emission bands. The PL is dominated by strong core emission from core electronic states that serve as the primary radiative pathway. Dual excitation‐independent and excitation‐dependent PL behavior was also observed, unveiling a complex emission mechanism involving hierarchical electronic transitions from core states, interface regions, and surface‐localized states. The observed luminescence originates from synergistic interactions between the carbon dot core and its nitrogen‐functionalized surface, rather than from discrete localized electronic transitions. Investigations revealed exceptional stability characteristics, including sustained photoluminescence under continuous UV irradiation, storage stability, and remarkable pH resilience across a wide range (pH 3–14). The preservation of PTCDA‐like domains, coupled with nitrogen‐induced electronic modifications, results in a unique class of high‐quantum‐yield (QY = 49.7%), bright‐green, fluorescent carbon dots that combine the advantages of molecular fluorophores with the versatility of carbon nanomaterials. This work provides fundamental insights into the structure–property relationships of surface‐functionalized nitrogen‐doped carbon dots and establishes their potential for a range of applications.