IR Luminescence
Definition
Emission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing differentiation of inks that appear identical in the visible spectrum.
- Excitation range
- Visible light at 450-600 nm
- Detection range
- Near-infrared emission from 700-1000 nm
- Primary use
- Differentiate inks that appear identical in visible light, especially in document alterations and reproduction fraud
Common questions
How does IR luminescence expose document alterations?+
When an altered document is illuminated with visible light (450-600 nm), different inks luminesce at different intensities in the near-infrared range (700-1000 nm). Two inks that look identical in normal light will show distinctly different emission levels, revealing where one ink was added or substituted for another.
Why might two inks look the same under normal light but different under IR?+
Different ink formulations contain different dye molecules. While they may reflect visible light similarly, their ability to absorb visible light and re-emit it as near-infrared radiation varies. This spectral fingerprint is unique to each ink, making IR luminescence a powerful way to compare them.
What wavelengths are actually used in IR luminescence testing?+
Documents are typically excited with visible or short-wave light (450-600 nm wavelengths). The emitted near-infrared radiation is captured and analyzed in the range of 700 to 1000 nanometers, which falls within the near-IR portion of the spectrum.
Related terms
- ESDA
- Electrostatic Detection Apparatus; detects latent indentations in paper by charging the surface and cascading toner particles, revealing tracing stylus pressure and writing...
- Video Spectral Comparator (VSC)
- A multispectral imaging instrument combining UV, visible, and near-infrared illumination with selectable emission filters and a calibrated digital camera; the primary bench...
- VSC-8000
- Video Spectral Comparator by Foster + Freeman, the standard QD instrument in CFSL and GEQD labs, with broadband visible, UV (254, 365...
- Acid-Free Packaging
- Paper folders or envelopes manufactured without acidic buffers, used for long-term storage of questioned documents to prevent acid-catalysed paper and ink degradation.
- Addition (Interlineation, Insertion)
- Fresh writing squeezed between lines, in margins, after the last entry, or in blank spaces left in the original document. Often shows...
- Alteration
- Any change made to a document after its original execution, including erasure, obliteration, addition, substitution and overwriting. A material alteration changes the...
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- ENFSI Document and Handwriting Working Group
- The European Network of Forensic Science Institutes working group responsible for harmonising best-practice guidelines for forensic document examination across European national laboratories.
- Erasure (Chemical)
- Removal of ink by bleaching or oxidising agents such as sodium hypochlorite, chloramine T, oxalic acid, potassium permanganate or hydrogen peroxide. Leaves...
- Erasure (Mechanical)
- Physical removal of writing by rubber, knife, scalpel blade, sandpaper or eraser. Disturbs paper fibres, thins the paper, and lifts the sizing...
- ESDA (Electrostatic Detection Apparatus)
- A non-destructive technique for detecting indented impressions on paper caused by writing pressure. A physical ink signature on paper produces detectable ESDA...
- Foster+Freeman VSC8000
- The current-generation forensic document examination workstation produced by Foster+Freeman Ltd (UK), used by the FBI Laboratory, DSTL (UK), CFSL (India), AFP (Australia),...
Explained in these topics
- Examination of Alterations: Erasures, Obliterations and AdditionsExcitation in the visible (450 to 600 nm) and detection in the near-IR (around 700 to 1000 nm). Two visually identical inks can luminesce differently under IR,...
- Detection Methods: Oblique, Transmitted, UV, IR and the VSCEmission of near-infrared radiation by ink dye molecules when excited by visible light; different ink formulations luminesce at different intensities, allowing...
- Lab Equipment, Evidence Handling and Chain of Custody in QDEExamination capturing the long-wavelength emission from inks excited at near-IR wavelengths; provides an additional spectral layer beyond IR reflectance for in...
- Reproduction of Documents: Photographic and Mechanical MeansDocument is illuminated with visible or short-wave light and the emitted IR (typically 750 to 1000 nm) is captured to differentiate inks that look identical in...