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

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.