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Journal of Forensic Identification28 / 62 (1), 2012

1 Internal Security Agency, Warsaw, Poland2 Lasar Elektronika, Warsaw, Poland3 University of Warmia and Mazury, Olsztyn, Poland

Received December 9, 2010; accepted March 1, 2011

Technical Note

Applying Anti-Stokes Phosphors in Development of Fingerprints on Surfaces Characterized by Strong Luminescence

Bogdan Drabarek 1 Antoni Siejca 2 Jarosław Moszczyński 3 Barbara Konior 1

Abstract: Using traditional luminescence methods to develop latent prints becomes problematic when dealing with backgrounds that dem-onstrate strong luminescence. In such instances, the application of time-resolved luminescence is considered a good solution. However, this technique requires the use of complicated devices that allow short-lived background f luorescence to be chopped off from a longer-lived f ingerprint luminescence. This paper discusses a new and straightfor-ward technique for the development of latent prints that involves using pigments with upconversion properties (anti-Stokes phosphors). The method requires an illumination source that emits infrared radiation.

IntroductionLuminescence methods that are commonly used to develop

latent prints are mainly based on excitation radiation in the 300–700 nm range and optical f iltration of the observed latent image by means of edge or bandpass filters [1, 2]. This method is not eff icient on surfaces that exhibit strong luminescence. To overcome this problem, various optoelectronic devices using time-resolved luminescence have been designed. Sophisticated

Journal of Forensic Identification62 (1), 2012 \ 29

devices, requiring the application of advanced and usually costly technology, allow short-lived background f luorescence to be chopped off from a longer-lived fingerprint luminescence [3–6].

The proposed method is based on multiphoton absorption, the upconversion process [7, 8]. It involves the use of formulations containing f luorescent pigments inconsistent with Stokes rule (e.g., anti-Stokes phosphors), as well as infrared radiation (IR) as the excitation source. The method enables the acquisition of luminescent fingerprints while eliminating background signals. This is the effect of low-energy IR radiation, which does not excite luminescence of typical dyes.

Anti-Stokes Phosphors Pigments called anti-Stokes phosphors belong to the group of

luminophores consisting of f luorides, zinc, strontium, or lantha-num oxides as well as trivalent ion admixtures of rare-earth activated compounds, such as thulium, erbium, ytterbium, and yttrium. They find their application in optoelectronics, biology, and often in marking documents and valuables, such as works of art. These pigments are sold as powders characterized by high chemical and temperature stability. Their emission frequency is found in the longer absorption frequency, that is, while excit-ing with radiation in the range 800–1000 nm, they emit visible light that depends on the phosphor’s composition. This type of location of absorption and emission bands is referred to as anti-Stoke shifts [7].

The mechanism of f luorescence of the aforementioned pigments is based on two- or multiphoton absorption. Optically active ions with relatively constant energy levels placed at regular intervals may absorb two or more photons of the same wavelength. In the f irst stage, excitation to a higher metasta-ble energy level of low likelihood of emission takes place. The second stage of absorption involves further excitation to a short-lived level, from where a radial transition to a basic level brings about f luorescent radiation of a shorter length than in the case of excitation radiation. Depending on the construction and compo-sition of the upconversion pigment, another mechanism is also possible, which involves transfer of energy between pigment components of various ions [8].

The purpose of the research performed at the Internal Security Agency (Warsaw, Poland) was to examine the potential of IR radiation of the 900–1000 nm range and pigments characterized


by upconversion in the development of f ingerprints as well as the impact on improving the legibility of fingerprints developed through the elimination of background signals.

Materials and MethodDuring the examination, latent prints were developed that had

been previously deposited on multicolored plastic surfaces and showed multirange strong luminescence excited with 240–760 nm radiation. On the other hand, these backgrounds did not show any luminescence when excited with 900–1000 nm radiation.

In the process of the development of the latent prints, a pigment showing upconversion characteristics, marked as UP54, as well as its mixture (1:1 ratio) with white B-400 and B-432 powders (BVDA), were used. UP54 pigment is deprived of the adhesion properties of typical f ingerprint powder. It demon-strates two kinds of luminescence:

• Stokes, in the yellow range of white light at UV excita-tion of approximately 360 nm

• anti-Stokes, in the green range of white light at excita-tion with 940–980 nm radiation (near IR)

Latent prints were developed only with the UP54 pigment or its mixture with the previously mentioned fingerprint powders. For comparison purposes, the cyanoacrylate method was applied, and f ingerprints treated with that method were subsequently contrasted with f luorescent dyes, such as ardrox, basic yellow, or safranine.

For the purpose of this investigation, the following excitation generating devices were used:

• illumination source for acquisition of f ingerprints in IR Micro Identif ication Chamber (MIC) (Lasar Elecktronika, Warsaw, Poland); radiation range of more than 900 nm (Figure 1)

• xenon illumination source for forensic purposes (Mult iKolor 10Xe, Lasar Eleckt ronika, Warsaw, Poland) of 350–1800 nm radiation range

A set of edge filters (symbols: KG3+T, 1KG3+T, 2KG3+T ) enabling excitation IR radiation to be cut off and visible radiation in the green range to be passed were used to take photographs of fingerprints illuminated with IR radiation.


For comparison purposes, f ingerprints were also recorded with the use of white light and UV radiation. Photographs of developed fingerprints excited with MIC and MultiKolor 10Xe illumination sources were taken with a Canon EOS 5D camera, 100 mm f/2.6 macro USM lens, in .jpg and .raw formats. An electro-optical analog-to-digital imaging system for acquisi-tion of f ingerprints by means of time-resolved luminescence (TRL) [6] was used to record the results with the use of the IR pulse illumination source. Recorded graphic files were viewed in Adobe Photoshop CS3.

Results and DiscussionFingerprints were developed only with the use of UP54

pigment and its mixture with two BVDA powders. Additionally, both the pigment and its mixtures were used for contrasting fingerprints developed with cyanoacrylate.

Reference material consisted of fingerprints developed with cyanoacrylate and contrasted with f luorescent dyes (ardrox, basic yellow, safranine).

The best results were obtained while using UP54 pigment alone on “fresh” fingerprints. The pigment poorly deposited on older (one-week-old) fingerprints. This probably stems from the fact that the pigment lacks the adhesion properties of typical f ingerprint powder and demonstrated poorer adhesion when

Figure 1Illumination source for acquisition of fingerprints in IR. MIC device consists of chamber with illumination source (in the middle), power

supply, reduction rings, filter, and magnifying glass.


applied to older fingerprints. Slightly better results in developing older fingerprints were achieved with use of the UP54 pigment mixture with BVDA white fingerprint powders. However, these mixtures demonstrated remarkably lower IR luminescence when compared to the pigment alone. Attempts to contrast cyanoacry-late-developed fingerprints with UP54 alone or its mixtures with powders did not yield positive results. Figures 2a through 2c present fingerprints developed on the same background by means of the cyanoacrylate method followed by contrasting with dyes (ardrox, basic yellow, safranine) and illuminated with appropri-ately suited excitation radiation (350–505 nm), whereas Figure 2d shows a fingerprint developed with UP54 pigment alone (with no prior cyanoacrylate treatment) and illuminated with IR radia-tion. In these figures, one can easily observe that the background luminescence in IR is significantly lower than in the case of the application of UV and visible light, which contributes to the fact that a developed fingerprint is better when viewed in the visibile range and illumintated with IR radiation.

(a) (b)

(c) (d)Figure 2

Fingerprints developed with cyanoacrylate and contrasted with the following dyes: (a) ardrox; (b) basic yellow; (c) safranine.

(d) Fingerprint developed with UP54 pigment alone.


Additional attempts to record fingerprints developed with the UP54 pigment on surfaces exhibiting strong f luorescence were carried out. For this purpose, boxes with f luorescent powder were used as backgrounds, and they demonstrated emission in red and green colors. Fingerprints deposited on these boxes were developed with the UP54 pigment and photographed with the use of UV radiation, white light, and IR radiation. The best results were obtained while applying IR illumination, which caused the excitation of a fingerprint alone and not the background f luores-cence (Figures 3 and 4). Figures 3a and 3b show a fingerprint developed with the UP54 pigment on a box with red f luorescent powder and illuminated with visible and IR radiation; Figures 4a and 4b exhibit a fingerprint developed with the UP54 powder on a box with green f luorescent powder and illuminated with UV and IR radiation.

(a) (b)Figure 3

Fingerprints developed with UP 54 on red background: (a) white light; (b) IR light.

(a) (b)Figure 4

Fingerprints developed with UP 54 on green background: (a) UV light; (b) IR light.


Fingerprints developed with the UP54 pigment were also successfully recorded by means of the optoelectronic device TRL, which allows shor t-lived background f luorescence to be chopped off from a longer-lived fingerprint luminescence, consequently leading to the acquisition of nondisturbed latent print images.

ConclusionThese examinations demonstrated that upconversion pigments

may f ind application in the development of latent prints on surfaces characterized by strong luminescence. Their advantage lies in their potential to excite luminescence with IR radiation, whose energy is suff iciently low to avoid excitation of other dyes. Because of this feature, in many instances, a surface where a latent print was detected remained black.

Another advantage of upconversion pigments is their ability to demonstrate f luorescence emission in the range visible for the human eye, which allows the expert to assess the quality of a developed print visually, with no need to apply specialized equipment.

Upconversion pigments may also be employed for the visualization of latent prints with the use of time-resolved luminescence.

UP54 pigment and its mixtures with white f ingerpr int powders did not demonstrate characteristics of a good fingerprint powder because of their low adhesive property when applied to older f ingerprints and the ones developed with cyanoacrylate. Hence, there is a need for a continuation of research aimed at the production of good-quality powders or suspensions that contain mixtures of pigments with upconversion properties.

For more information, please contact:Jaroslaw Moszczynski03-126 Warszawaul. Picassa 9 m [email protected]


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3. Murdoch, R. H.; Menzel, E. R. Computer Interfaced Time-Resolved Luminescence Imaging System. J. For. Sci. 1993, 38 (3), 521–529.

4. Campbell, B. M. Time-Resolved Photography of Latent Prints on Fluorescent Backgrounds. J. For. Ident. 1993, 43 (4), 368–377.

5. Roorda, R. D.; Ribes, A. C.; Damaskinos, S.; Dixon, A. E.; Menzel, E. R. A Scanning Beam Time-Resolved Imaging System For Fingerprint Detection. J. For. Sci. 2000, 45 (3), 563–567.

6. Moszczyński, J.; Siejca, A.; Ziemnicki, Ł. New System for the Acquisition of Fingerprints by Means of Time-Resolved Luminescence. J. For. Ident. 2008, 58 (5), 515–523.

7. Wang, F.; Liu, X. Recent Advances in the Chemistry of Lanthanide-doped Upconversion Nanocrystals. Chem. Soc. Rev. 2009, 38, 976–989.

8. Auzel, F. Upconversion and Anti-Stokes Processes with f and d Ions in Solids. Chem. Rev. 2004, 104 (1), 139–174.

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