Lanthanide Luminescence and its Applications in Forensic Science

Lanthanide compounds, specifically those containing europium and terbium can exhibit luminescent properties when combined with ligands that promote this characteristic. Lanthanide luminescence has proven to have an array of useful applications, one of which is the formation of luminescent powders for exposure of latent fingerprints. The aim of this study was to synthesise a novel ligand to support luminescent character in europium and terbium compounds, and then dope these compounds in to talcum powder. This resulting powder would ideally give exposure of latent fingerprints that can then be enhanced, through excitation of the luminescent compounds dispersed in the powder. A novel (Me)₃CN(CH₂P(O)Ph₂)₂ ligand (p=o) was synthesised, and in turn was used to synthesis a range of Ln(β‐diketonate)₃(p=o) compounds. These compounds were assessed for potential luminescent activity, and doped into talcum powder. These powders were then appraised for their prospective use as latent fingerprint exposing agents. Through modification of a published procedure, the (Me)₃CN(CH₂P(O)Ph₂)₂ ligand was synthesised, and characterised by Electrospray Ionisation (ESI) Mass spectrometry, Nuclear Magnetic Resonance (NMR) spectroscopy, Infra‐red (IR) spectroscopy, melting point analysis and elemental analysis. With β‐diketonate ligands acetylacetone (acac) and thenoyltrifluoroacetone (tta), lanthanide metals lanthanum, europium and terbium and the (p=o) ligands a series of novel compounds were synthesised (Ln(β‐diketonate)₃(p=o)). These compounds were characterised by the methods listed above. Using the neutral ligands 1,10‐phenanthroline (phen) and 2,2‐bipyridine (bipy), a series of Eu/Tb(acac/tta)₃(phen/bipy) compounds were synthesised and doped into talcum powder, to investigate the effects on particle and structure character of the doped talcum powders. Talcum powder was also sonicated to investigate the effect of this on particle size, along with effect on use as a fingerprinting agent. Laser diffraction and Scanning Electron Microscopy studies informed of a notable decrease in particle size with sonication, and an increase in specific surface area. However the effect of this process on increasing exposure of latent fingerprints was deemed too insignificant to justify the procedure. The compounds Eu/Tb(acac/tta)₃(phen/bipy), (Eu/Tb(β‐diketonate)₃(p=o) and [H₂NMe₂]₃[Eu/Tb(2,6‐dpa)₃].2H₂O were investigated for luminescent activity. Fluorescence spectroscopy determined the dominant emission wavelengths from 254 nm and 312 nm excitation were at 510 nm and 625 nm respectively. The talcum powders, doped with the luminescent compounds were analysed for luminescent activity. Direct screening with an ultra‐violet (UV) lamp with emission wavelengths of 254 nm and 312 nm informed of the powders with the most intensely observed luminescent emissions. From these results, Eu(tta)₃(p=o), H₂NMe₂]₃[Eu(2,6‐ dpa)₃].2H₂O, Tb(acac)₃(p=o) and H₂NMe₂]₃[Tb(2,6‐dpa)₃].2H₂O were chosen as the most promising candidates for more in‐depth investigation of latent fingerprint exposure potential. Furthermore, it was determined that the novel (Me)₃CN(CH₂P(O)Ph₂)₂ ligand was successful as a neutral ligand for supporting luminescence. The powders were trialled by several variables, including surface, powder quantity, age of latent print, temperature, and the brush used to determine their effectiveness. Powders were compared to commercial Greenwop and Redwop fingerprint powders, as these were the most similar industrial samples in terms of use. Through trials in the laboratory and the police fingerprinting laboratory, it was determined that the doped talcum powders were inferior to the commercial “wop” samples in terms of latent print definition under UV conditions. However, the talcum powders had several useful applications, specifically the dual effect of exposing prints clearly under UV and non‐UV conditions. It was concluded the best application for the fingerprint powders was on smooth surfaces such as glass, with a gradual application of powder. Small amounts of powder gave more clarity under non‐UV print exposure, but higher quantities of powder were required to get ample luminescent intensity under UV conditions