Smart Fluorescence Tuning and Micelle-Stabilized White Light Emission via a Coumarin 102–Rhodamine B System: A Simple Path to Eclectic Color Luminescence for Anti-Counterfeiting Applications

The pursuit of simple, cost-effective, and emission color-tunable luminescent materials is gaining momentum due to their vast potential in emerging technologies. However, practical systems with high tunability, compatibility, and aqueous stability remain limited. In this work, we report a smart luminescent platform based on two well-known and sensitive organic fluorophores coumarin 102 (C102) and rhodamine B (RhB) that collectively deliver a broad color-tunable emission with minimal material incompatibility. C102 exhibits polarity and pH-dependent fluorescence shifts, while RhB responds sensitively to temperature changes, enabling multimodal modulation of emission through solvent polarity, pH, and temperature variations. A precise molar ratio (C102: RhB = 4:10) yields stable white-light emission (CIE: 0.33, 0.33) in an aqueous medium. Furthermore, the system offers multistate fluorescence switching driven by pH and thermal stimuli, enabling its use in reversible, water-based fluorescent security inks for concealment, revelation, and erasure-based encryption. Embedding the fluorophores within sodium dodecyl sulfate (SDS) micelles ensures emission stability and facilitates efficient Förster resonance energy transfer (FRET) (∼94%) from C102 to RhB in acidic aqueous environments. This eco-friendly and tunable system holds significant promise for next-generation anticounterfeiting, display, and biosensing technologies.