Unveiling Hidden Prints: Optically stimulated luminescence for latent fingerprint detection

Abstract

Fluorescent lighting and optical techniques have been widely utilized to enhance the detection of latent fingerprints. However, the development of new techniques is imperative to expand the range of surfaces from which latent fingerprints can be detected. When relying on traditional methods, fingerprint evidence can remain undetected or even disregarded due to insufficient detection and limited detail, especially when dealing with a luminescent background. In this study, we propose the utilization of optically stimulated luminescence (OSL) applied to a Ba₂SiO₄ matrix, co-doped with Eu²⁺ and Dy³⁺, as a powerful method for visualizing latent fingerprints on various surfaces, including thin plastic bags, rigid duct tape, thin aluminum foil, and glass slices. This technique effectively eliminates any luminescent background and significantly enhances optical imaging. This represents the first successful application of OSL in the development of latent fingerprints, thus paving the way for more efficient and effective forensic techniques in the future.

Keywords: Applied optics; Ba2SiO4; Fingerprint detection; Forensic applications; Optical stimulated luminescence.

Fig. 1

OSL mechanism: (1) irradiation and electron-hole pair generation; (2) charge carriers thermal relaxation; (3) electron trapping in the trapping sites and hole trapping in the activator site; (4) optically stimulated electron excitation in conduction band, (5) electron movement from trapping to activator site; (6) electron trapping in the activator site; (7) electron-hole recombination.

Fig. 2

XRD pattern of Ba₂SiO₄ powder. In the inset: crystal structure of the identified orthorhombic phase.

Fig. 3

PLE map of Ba₂SiO₄:Eu,Dy sample.

Fig. 4

Thermoluminescence of Ba₂SiO₄:Eu and Ba₂SiO₄:Eu,Dy sample.

Fig. 5

Emission spectra of Ba₂SiO₄ powders in a) photoluminescence (excitation wavelength: 365 nm), b) thermoluminescence at 150 °C, c) optically stimulated luminescence.

Fig. 6

a) photograph under room lighting and b) OSL imaging of the of a sample with Ba2SiO4 powders. c) OSL imaging setup composed by a LED source of optical stimulation, the sample, a shortpass filter for reflecting the diffused LED light and a camera for collecting the transmitted OSL signal.

Fig. 7

a), b), c): SEM images of different areas of a latent fingerprint developed with Ba₂SiO₄ powders; d), e), f): EDS maps of Ba, Si and O elements carried out in the same area of image c); g), h), i) SEM image of the latent fingerprint details at increasing magnification levels.

Fig. 8

OSL fingerprint imaging. The insets show the characteristic details of the fingerprint.

Fig. 9

OSL fingerprint imaging on a plastic bag after 48 h from fingerprint deposition (a)) and on a plastic tape right after fingerprint deposition and cyanoacrylate fuming.

Fig. 10

a) fluorescence imaging of latent fingerprint on glass above coumarine solution, b) fluorescence and c) optically stimulated luminescence imaging of latent fingerprint developed with Ba₂SiO₄ powder.