Photoluminescent europium(III) complex intercalated in natural and synthetic clay minerals for enhanced latent fingerprint detection

Abstract Fluorescent nanohybrid materials, europium(III) complex intercalated Na+-smectite clay minerals (synthetic hectorite and natural montmorillonite), have been developed to visualize latent fingerprints. The guest europium(III) complex ([EuCl2(Phen)2(H2O)2]Cl·H2O) was obtained by simple complex reaction between europium chloride hexahydrate (EuCl3·6H2O) and 1,10-phenanthroline (Phen) as a 1:2 molar ratio of Eu3 + ion to ligand molecules. The intercalated nanohybrids ([Eu(Phen)2]3 +-clay minerals) were obtained through ion exchange reaction of interlayer sodium cation with europium complex ion. Guest europium(III) complex and [Eu(Phen)2]3 +-clay mineral hybrids were characterized by powder X-ray diffraction, Fourier transform infrared, thermogravimetry-differential thermal analysis (TG-DTA), elemental analysis, UV–visible and fluorescence spectroscopy. The intercalated complex maintains a characteristic red 5D0–7F2 emission at wavelength 617 nm, which is comparable to that of the free complex. The 5D0–7F2 emission intensity of [Eu(Phen)2]3 +-laponite was ca. 3.5 times higher than that of [Eu(Phen)2]3 +-montmorillonite, due to the presence of quenching impurities in natural montmorillonite itself. Fingerprint residues on glass slides were harvested by using [Eu(Phen)2]3 +-clay mineral powders, resulting in good definition for enhanced latent fingerprint detection. Particularly, [Eu(Phen)2]3 +-hectorite hybrid powder was more clearly separated from the background compared to the montmorillonite hybrid powder.