23
VSC
®
: Anti-Stokes fluorescence
Excitation lig
(IR)
VSC
®
: Stimulating and viewing fluorescence (Infrared light)
Wavelength (nm)
Visual contrast
Visible fluorescence is stimulated in certain trace materials using narrow-band visible light. Differently coloured sources are
available to suit the type of trace deposit sought. The longer wavelength fluorescence must be viewed using a suitable
longpass filter.
Anti-Stokes fluorescence
Anti-Stokes fluorescence or IR Fluorescence 840-1100nm occurs in certain types of security inks and pigments. The process
differs from normal fluorescence in that the emission undergoes an anti-Stokes shift to a wavelength shorter than the excitation
radiation (i.e. a colour shift away from the excitation light, towards the blue end of the spectrum).
Narrowband excitation light
Absorption spectrum
VSC
®
: Stimulating and viewing fluorescence
Transmission spectrum of safe longpass viewing filter
Fluorescence emission
Wavelength (nm)
ht
Narrowband excitation light
Absorption
spectrum
Transmission spectrum of safe shortpass
viewing filter
Fluorescence emission