Use of Luminescence Modulation in a New Series of\nMixed Lanthanide Metal–Organic Frameworks for Selective Firearm\nAmmunition Marking

Metal–organic\nframeworks (MOFs) are coordination polymers\nthat can generally be described by secondary building units (SBUs).\nThese include lanthanide MOFs, specifically mixed lanthanide MOFs\n(m-LnMOFs), encompassing coordination polymers formed by two or more\ndifferent Ln<sup>3+</sup> ions. These compounds have been the subject\nof study by inorganic chemists worldwide, mainly due to the possibility\nof obtaining long-awaited tunable luminescence, i.e., compounds that\nemit luminescence in various visible spectrum regions. A wide range\nof emission color scan be obtained by inserting different Eu<sup>3+</sup>, Tb<sup>3+</sup>, and Gd<sup>3+</sup> ion molar fractions in m-LnMOFs,\nwhich can also be adjusted by choosing the Ln<sup>3+</sup> ion or\nits amount in each network. This study presents a new series of m-LnMOFs\nsupported by 1,2,4,5-benzenetetracarboxylic acid (H<sub>4</sub>btec).\nThese compounds were completely characterized in their solid state\nthrough different analytical and spectroscopic techniques, and an\nin-depth photophysical study was conducted. Due to their high thermal\nstability and multicolored emissions, these complexes were applied,\nfor the first time, as selective ammunition markers, allowing for\nthe unequivocal identification of the type of weapon used in forensic\nscenarios and the promotion of stricter ammunition trade control.