Yttrium orthovanadates phosphors as up-conversion luminescent markers for gunshot residue identification

In this work, yttrium orthovanadate phosphors doped with Er3+ and Yb3+ (YVO4: Er3+, Yb3+) were synthetized by the combustion method. After a post-synthesis heat treatment (1100 °C for 6 h), samples were highly crystalline, with only the tetragonal zircon phase remaining. Additionally, all samples presented promising down and up conversion properties, exhibiting a strong green luminescence when excited by either UV or IR radiation. The up-conversion process involved the absorption of two-photons, with the intensity of the Er3+ transitions (2H11/2–4I15/2, 4S3/2–4I15/2 and 4F9/2–4I15/2) heightened with the Yb3+ content. The co-doped orthovanadate samples were introduced into 9 mm non-toxic ammunition (NTA) for evaluation as luminescent markers for gunshot residues (GSR). After shots with marked ammunition were fired, these phosphors enabled the visual detection of luminescent GSR (LGSR) on the shooter, firearm and firing place, facilitating an analysis of the simulated crime scene. These residues also presented a chemical signature that enabled their identification as LGSR. Besides, the down and up conversion properties observed in the residues provide an additional security feature for the unequivocal characterization of the LGSR.