[Ln2(BDC)3(H2O)4]n: A low cost alternative for GSR luminescent marking

This paper reports on the development of low cost luminescent markers for gunshot residue (GSR) identification by a new room temperature precipitation synthesis route. These markers are metal-organic frameworks (MOFs) formed by the ligand 1,4-H2BDC (teraphthalic acid) and the metals Zn2+, Eu3+ and Tb3+. The MOFs were synthesized by precipitation, using different ratios of zinc and lanthanides (1-100%). The synthesized MOFs were added to 9 mm NTA gunpowder and, after shots were fired, luminescent residues (LGSR) were visualized under UV radiation. The residues were collected and characterized by non-destructive techniques such as SEM-EDS and emission spectroscopy. All MOFs presented high luminescence. However, those with levels of Eu3+ above 10% or Tb3+ above 5% presented the best cost-benefit. Comparing with the marker containing only lanthanide ions, this represents a cost reduction of up to 7-times. Besides, the precipitation synthesis represents an innovation in developing crystalline, high luminescent and stable luminescent markers for GSR identification.