High-Efficiency Fingerprint Detection Based on Eu³⁺-Doped AgYMo₂O₈ red Phosphors Optimized by Hydrothermal Method

In forensic science, latent fingerprints represent a crucial type of evidence for individual identification. Nevertheless, the features of such fingerprints exist at a microscopic scale. The application of fluorescent powder during the development of latent fingerprints can markedly improve image contrast while reducing background interference, thus enabling the acquisition of high-quality fingerprint images. In the present work, AgYMo₂O₈:Eu³⁺ red fluorescent powder was successfully synthesized using both solid phase and hydrothermal methods. X-ray diffraction (XRD) together with Rietveld refinement was employed to confirm the phase structure of the obtained samples. A high energy absorption efficiency exists within the charge transfer band from [MoO₄]^2- to Eu³⁺, which leads to efficient red-light emission and the production of a high contrast background light. Under excitation at 465 nm, the Eu³⁺ doped samples exhibit red emission at 616 nm, with an optimal doping concentration determined to be 0.40 mol. The primary mechanism behind concentration quenching is the interaction between the nearest neighboring ions. The prepared samples possess high thermal stability and outstanding thermal stability. After five thermal cycles, the luminescence intensity of the material recovered to approximately 99%. Among the two methods, the samples optimized by the hydrothermal route display a homogeneous particle size distribution and good dispersion. These samples can clearly reveal the level I to level III structures of fingerprints and are well suited for fingerprint visualization on various substrate materials. Overall, both synthesis approaches yielded powders that showed excellent sensitivity, selectivity, and contrast accompanied by minimal background interference. These results fully demonstrate the application potential of AgYMo₂O₈:Eu³⁺ in the field of latent fingerprint imaging.