Facile preparation strategy of multicolor room temperature phosphorescent carbon dots for fluorescence interference-free latent fingerprint visualization

Latent fingerprint visualization is usually interfered by background fluorescence of substrates. The room temperature phosphorescent carbon dots (CDs) can effectively eliminate background fluorescence interference through their afterglow properties. However, developing CDs with multicolor room temperature phosphorescence (RTP) as fingerprint reagents remains a significant challenge. In this study, multicolor RTP CDs were synthesized via a facile one-step pyrolysis using benzamide and boric acid as precursors. The tunable phosphorescence color was achieved via regulating the amount of benzamide and reaction temperature. The prepared CDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible absorption spectra, and photoluminescence spectra. The results indicated that synthesized CDs were amorphous structures, sphere-like in shape with good dispersibility, and rich in functional groups on the surface. The three CDs exhibited blue, cyan, and green phosphorescence emission after UV lamp cessation. Based on the multicolor phosphorescence properties, the prepared CDs were successfully applied to interference-free development of latent fingerprints (LFPs) on various fluorescent substrate surfaces. All three CDs achieved high-quality fingerprint imaging on the selected substrates with well-defined details. Compared to single-color CDs, multicolor CDs could provide flexible selection for achieving high-contrast imaging on complex fluorescent substrates.