Energy‐Efficient Synthesis of Multicolor Carbon Dots: Revealing the Role of Core Size and Surface States on Photoluminescence and Electrochemiluminescence for Anticounterfeiting

Abstract Carbon dots (CDs) hold immense potential for various optical applications, however, the economical and mild preparation of multicolor carbon dots (MCDs) remains challenging, and the correlation between their photoluminescence (PL) and electrochemiluminescence (ECL) is still unclear. In this study, five MCDs with emissions from blue to red are rapidly synthesized using a mild one‐step ion liquid‐assisted wet chemical method under atmospheric pressure, with 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) as the reaction medium. The resulting MCDs exhibit sizes ranging from 1.81 to 3.15 nm, featuring similar surface structures. The MCDs as models are used to investigate how the core size and surface state determine their PL and ECL. It is found that PL primarily arises from excitation and emission within the core, whereas ECL is governed by surface states. Notably, all MCDs exhibit a near‐infrared ECL emission ≈760 nm, which is red‐shifted relative to their PL and remains independent of particle size. Leveraging their tunable multicolor luminescence, pH‐ and solvent‐dependent emission properties, and screen‐printing compatibility, MCDs as luminescent tracers are developed for anticounterfeiting and freshness indicators. This study advances the synthesis of full‐color CDs and offers valuable insights into the modulation of their luminescent properties, expanding their potential applications.