Solvent-Free Synthesis of Highly Luminescent Solid-State Boric Acid-Assisted Carbon Dots for Stable and High-Contrast Latent Fingerprint Visualization

Abstract The development of efficient, stable, and environmentally friendly fluorescent materials for latent fingerprint visualization remains a major challenge in forensic science. Carbon dots (CDs) have emerged as promising fluorescent nanomaterials owing to their low toxicity, tunable optical properties, and eco-friendly nature. However, their practical application in solid-state systems is often hindered by aggregation-induced quenching (AIQ), which can significantly suppress fluorescence emission. In this study, highly luminescent boric acid-assisted carbon dots (B-CDs) were synthesized through a simple, rapid, and solvent-free thermal process using citric acid, urea, and boric acid as precursors. Unlike conventional approaches, the developed method enables the direct formation of solid-state emissive carbon dot powders without requiring additional surface passivation, purification, or polymeric matrices. Structural and spectroscopic characterizations supported the successful formation of heteroatom-functionalized B-CDs that exhibit excitation-dependent photoluminescence and strong solid-state emission. The synthesized B-CDs exhibited a high solid-state photoluminescence quantum yield of 77.5%. The B-CDs showed strong short-term stability, retaining more than 95% of their initial PL intensity after 60 min exposure to 95% relative humidity and during short-term thermal treatment up to 90 °C. Long-term measurements showed approximately 57% PL retention after 5 days at 95% relative humidity and approximately 48% after 5 days of thermal aging at 50 °C, while approximately 92% of the initial PL intensity was retained after 5 days of continuous UV irradiation. The proposed solvent-free synthesis strategy offers a simple and potentially scalable route for producing strongly emissive solid-state carbon dots, highlighting their potential for latent fingerprint visualization.