Abstract: A series of rare earth fluorescent complexes containing Europium (Eu) were synthesized via a precipitation approach, using o-, m-, p-methylbenzoic acid (o-, m-, p-MA) as the first ligand, respectively, and o-phenanthroline (o-Phen) as the second ligand. Their synthetic conditions were also optimized systematically, including the category of ligands, the molar ratio of ligands, pH, reaction temperature, and reaction time. The powders of these as-prepared[Eu(m-MA)₃(o-Phen)] complexes were then used to develop the latent fingerprints on various of smooth substrates. In addition, the contrast, sensitivity, and selectivity for fingerprint development were investigated in detail. The results showed that the contrast between the developed fingerprint and the substrate was quite high, under the excitation of 254 nm ultraviolet light. The friction ridges were coherent and sharp enough, even the minutiae features of the friction ridges could be clearly observed. The fluorescent developing powders were adsorbed only on the friction ridges, rather than the furrows. Therefore, our rare earth fluorescent complex based fingerprint development could exhibit strong contrast, high sensitivity, and good selectivity.

Key words: fingerprint development, latent fingerprint, europium, complex, fluorescent materials