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In this work, we investigated the potential of Eu[sup.3+]/Dy[sup.3+]-codoped Y[sub.2]Sn[sub.2]O[sub.7] fluorescent nanophosphors to visualize latent fingermarks. We prepared these nanophosphors with various doping concentrations by the conventional coprecipitation reaction. The crystal structure, morphology, luminescence properties, and energy transfer mechanisms were studied. The crystalline phase was characterized by X-ray diffraction and crystal structure refinement using the Rietveld method. XRD measurements showed that the samples crystallized in the pure single pyrochlore phase with few more peaks originated from secondary phases and impurities generated during phosphor production, and that Eu[sup.3+] ions occupied D[sub.3d] symmetry sites. The average crystallite size after mechanical grinding was less than 100 nm for all compositions. The optical characterization showed that, when excited under 532 nm, the Eu[sup.3+]/Dy[sup.3+]-codoped Y[sub.2]Sn[sub.2]O[sub.7] samples’ main intense emission peaks were located at 580–707 nm, corresponding to the [sup.5]D[sub.0]→[sup.7]Fj (j = l, 2, 3, and 4) transitions of europium. In fact, the [sup.5]D[sub.0]→[sup.7]F[sub.2] hypersensitive transition is strongly dependent on the local environment and was quite weak in Eu[sup.3+]:Y[sub.2]Sn[sub.2]O[sub.7] at low Eu[sup.3+] doping levels. We found that the presence of Dy[sup.3+] as a codopant permitted enhancing the emission from this transition. The calculated PL CIE coordinates for the synthesized nanophosphors were very close to those of the reddish-orange region and only slightly dependent on the doping level. Various surfaces, including difficult ones (wood and ceramic), were successfully tested for latent fingerprint development with the prepared Eu[sup.3+]/Dy[sup.3+]-codoped Y[sub.2]Sn[sub.2]O[sub.7] fluorescent nanophosphor powder. Thanks to the high contrast obtained, fingerprint ridge patterns at all three levels were highlighted: core (level 1) islands, bifurcation, and enclosure (level 2), and even sweat pores (level 3).