Plasma‐Tailored Carbon Dots with Atomic‐Level sp ² /sp ³ Hybridization for Programmable Band Structures and Optothermal Functionality

Controlling sp²/sp³ 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 sp²/sp³ 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 sp² 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.