Plasma‐Tailored Carbon Dots with Atomic‐Level sp2/sp3 Hybridization for Programmable Band Structures and Optothermal Functionality

Abstract Controlling sp 2 /sp 3 hybridization in carbon nanomaterials with precision is critical for tuning their electronic and optical properties and enhancing their functionality; however, achieving this under energy‐efficient and eco‐friendly conditions remains challenging. A modular plasma nanoengineering approach is presented that enables atomic‐level control of hybridization in zero‐dimensional carbon dots (CDs) using ambient‐pressure microplasmas. By adjusting the plasma energy via discharge current and capillary confinement, the sp 2 /sp 3 ratio is programmed to produce adjustable optical bandgaps (2.75–3.1 eV) and phase‐dependent optothermal responses. The plasma‐synthesized CDs demonstrate stable photoluminescence (PL)‐based thermal sensitivity of up to 1.38% °C −1 , outperforming traditional semiconductors and carbon materials. Microscopic and spectroscopic studies identify an optimal sp 2 content (≈84%) that maximizes the phonon–exciton coupling and enhances the thermal control of PL. This catalyst‐free, low‐temperature method offers a scalable and sustainable pathway for customizable carbon nanomaterials, paving the way for wearable, implantable, and optoelectronic sensor applications.