Fluorescence color tuning of dual-emission carbon quantum dots produced from biomass and their use in Fe3+ and Cu2+ detection

• Dual-emission biomass carbon quantum dots (D-BCQDs) were synthesized from Viburnum awabuki leaves via a simple, eco-friendly ethanol solvothermal method. • The fluorescence color of D-BCQDs can be tuned from crimson to blue-gray by adjusting the solvothermal temperature (140–240 °C), with two emission peaks at 490 nm and 675 nm under 413 nm excitation. • Surface oxidation defects, nitrogen content, and sp2-C/sp3-C hybridized domains are the main factors determining the fluorescence color. • The D-BCQDs enable ratiometric detection and quantification of Fe3+ and Cu2+ ions, including simultaneous detection in mixed solutions.