Blue-emitting bismuth-doped lanthanum oxide (La₂O₃: Bi³⁺) with various concentrations of Bi was synthesized using the sol–gel combustion method and used for visualization of latent fingerprints (LFPs). An X-ray diffraction (XRD) study revealed the hexagonal structure of the phosphors and total incorporation of the bismuth in the La₂O₃ matrix. Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used to study the morphology and the relative vibrations of the synthesized samples. Photoluminescence (PL) studies showed strong blue emission around 460 nm due to the ³P₁ → ¹S₀ transition. Clear bright-blue fingerprint images were obtained with the powder dusting method on various surfaces like aluminum, compact discs, glass, wood and marble. A first evaluation of these images indicated a clear visualization of all three levels of details and a very high contrast ranging from 0.41 on marble to 0.90 on aluminum. As a further step, we used an algorithm for extracting fingerprint minutiae with which we succeeded in detecting all three levels of fingerprint details and even the most difficult ones, like open and closed pores. According to these analyses, La₂O₃: Bi phosphor is demonstrated to be an effective blue fluorescent powder for excellent visualization of latent fingerprints.

Undoped Y₂Sn₂O₇ and Eu³⁺ doped Y₂Sn₂O₇ samples with doping concentrations 7%, 8%, 9%, and 10% are successfully synthesized by the co-precipitation method. A complete structural, morphological, and spectroscopic characterization is carried out. XRD measurements reveal that samples crystallize in the pure single pyrochlore phase and Eu³⁺ ions occupy sites with D_3d symmetry. After mechanical grinding, the average crystallite size is less than 100 nm for all compositions. Optical characterization shows emission from the ⁵D₀ level towards the lower lying ⁷F_0,1,2,3,4 levels. The CIE color coordinates of all the pyrochlore phosphors are very close to those of the ideal red light. For the visualization of latent fingerprints, different surfaces are tested, including difficult ones (wood and ceramic), with excellent results. All three levels of fingerprint ridge patterns are visualized: core (Level 1), bifurcation and termination (Level 2), and sweat pores (Level 3). Moreover, our nano-powders are used to prepare a stable fluorescent ink.

In this work, we investigated the potential of Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ 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 Eu³⁺ ions occupied D_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 Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ samples’ main intense emission peaks were located at 580–707 nm, corresponding to the ⁵D₀→⁷Fj (j = l, 2, 3, and 4) transitions of europium. In fact, the ⁵D₀→⁷F₂ hypersensitive transition is strongly dependent on the local environment and was quite weak in Eu³⁺:Y₂Sn₂O₇ at low Eu³⁺ doping levels. We found that the presence of Dy³⁺ 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 Eu³⁺/Dy³⁺-codoped Y₂Sn₂O₇ 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).