Tunable‐Wavelength Broadband Liquid‐State Carbon‐Quantum‐Dot Lasers

Abstract Stimuli‐responsive carbon quantum dots (CQDs) are versatile, solution‐processable, liquid‐state gain media with broadband spectral tunability spanning ultraviolet to near‐infrared wavelengths, attributed to their surface functionalization capabilities and environmental sensitivity. However, their application in high‐coherence light sources is constrained by inherent scattering losses and lower gain coefficients relative to conventional colloidal quantum dots. To address these limitations, concentration‐dependent photoluminescent are engineered CQDs integrated into an index‐matched cuvette‐based cavity, enabling tunable liquid‐state lasing across the 641–710 nm spectral range via the Förster resonance energy transfer (FRET) effect. The FRET‐optimized CQDs exhibit minimized beam divergence emission, facilitating efficient coupling with an external optical cavity—comprising an aluminum mirror positioned outside the cuvette‐based cavity. By modulating the external optical feedback, controlled transitions from random lasing to Fabry–Pérot multimode, and single‐mode lasing regimes are achieved. Notably, this design methodology is applicable to colloidal quantum dots as liquid‐state gain media, establishing a versatile platform for spectrally tunable lasing sources. This work bridges the gap between solution‐processable nanomaterials and functional laser devices, advancing prospects for integrated photonic systems.