Functionalized surfaces created by perturbation in luminescent polymer nanocomposites: Materials for forensic and security ink applications

Exploring Optically Stable Reddish-Orange Fluorescent Magnetic Pigment (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ for Anti-counterfeiting Applications

The (0.90)Y2O3:(0.10-x)Eu3+:(x)Bi3+ nanophosphors (0.00 ≤ x ≤ 0.06) are synthesised using chemical combustion citrate route and characterized via X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV- visible and photoluminescence spectroscopy. The scanning electron micrographs indicate that the grain size of the phosphors ranges between 40 to 50 nm. The photoluminescence (PL) spectra, acquired under the excitation wavelength of 365 nm of ultraviolet light, show emission peaks at wavelengths 580 nm, 586-598 nm, 610 nm, 629-661 nm and 686-695 nm corresponding to the 5D0 → 7FJ electronic transitions of the Eu3+ ion with J = 0, 1, 2, 3 and 4, respectively. The most intense PL spectra at 611 nm (5D0 → 7F2), showcasing reddish-orange emission, indicate a higher concentration of Eu3+ ions in asymmetric sites within the Y2O3 host matrix. The presence of the distinct electronic transitions of Eu3+ in PL spectra acclaims that Bi3+ ions transfer their energy efficiently to Eu3+ ions in the matrix. Physical and chemical tests are being conducted on nanophosphors with Bi3+ substitutional doping of x = 0.02 and x = 0.04, both demonstrating intense PL emission. Magnetisation measurements suggest the soft magnetic nature of the nanophosphors, attributing it to the presence of Eu3+ ions in the 7F2 state. The highest PL intensity is seen in the nanophosphor (x = 0.04) with substitutional doping of 6% of Eu3+ and 4% of Bi3+ in Y2O3. This nanophosphor also demonstrates excellent optical stability in the investigated conditions and exhibits soft magnetic behaviour, positioning it as a promising material for incorporation as a fluorescent magnetic pigment in security ink applications. These features serve to prevent counterfeiting of secured documents both optically and magnetically.

Nanosheets of two-dimensional photoluminescent lanthanide phosphonocarboxylate frameworks decorated with free carboxylic groups for latent fingerprint imaging

The synthesis, structural characterization, exfoliation, and photophysical studies of two-dimensional (2-D) lanthanide phosphonates, named Ln(m-pbc); [Ln(m-Hpbc)(m-H₂pbc)(H₂O)] (Ln = Eu, Tb; m-pbc = 3-phosphonobenzoic acid) based on the phosphonocarboxylate ligand, are reported. These compounds are neutral polymeric 2D layered structures with pendent uncoordinated carboxylic groups between layers. The nanosheets were obtained by a top-down strategy involving sonication-assisted solution exfoliation and characterized by atomic force microscopy and transmission electron microscropy, showing lateral dimensions from nano- to micro-meter scales, and thicknesses down to several layers. The photoluminescence studies demonstrate that the m-pbc ligand acts as an efficient antenna toward Eu and Tb(III) ions. The emission intensities of dimetallic compounds are clearly enhanced after incorporation of Y(III) ions due to the dilution effect. Ln(m-pbc)s were then applied for labelling latent fingerprints. It is worth noting that the reaction between active carboxylic groups and fingerprint residues benefits the labelling, showing efficient imaging for fingerprints on all kinds of material surfaces.