We have four classes of IR invisible marking products:

• IR Down-Conversion: Visible to IR, and IR to IR
• IR Up-Conversion:  IR to Visible (anti-stokes shift)
• Black Visible - Black IR and Black Visible - Clear IR inks and pens
• Clear Visible and Dark IR Pigment Absorber - Non-Fluorescing

Our IR Fluorescent Items

1. IR Ink writing pens:  Our IR ink writing pens writes in a nearly invisible ink which will fluoresce in the infrared spectrum.  Using a 630nm red filter, you can see the IR1 ink.  We have two types of infrared inks: IR1 peak excitation is at 793nm and peak emission at 840nm while our IR2 ink has a peak excitation at 824nm and peak emission at 885nm.   The IR1 Ink has very similar excitation and emission peaks to Indocyanine Green (ICG) but the IR1 ink is much more stable.  Once ICG is mixed with water, it has a lifespan of less than 24 hours.  The IR1 ink in the pen will last for months though it will fade in sunlight after about 1 week.
   
2. IRDC2:  Visible to infrared fluorescing powder.  When stimulated with a blue or red light, the powder will fluoresce in the infrared range.
3. IRUCG, IRUCR, IRUCB:  Infrared to visible fluorescing powder.  When stimulated with infrared light, the powder will fluoresce in the visible range.

 Up / Down Conversion refers to the fluorescence shift up or down the spectrum from the excitation source.  All fluorescence occurs when a material is stimulated with energy (usually light) at one frequency (say a black light) and the material remits some of the energy at a lower frequency (your typical fluorescent paints the glow in the human visible range).  

 Fluorescence can occur at any point of the electromagnetic spectrum.  Different materials exhibit different fluorescent properties.  A material might absorb ultraviolet light and emit visible light, or absorb visible and emit infrared, or absorb near infrared and emit far infrared.  

 Fluorescence almost always occurs as a shift down in photon energy levels or down-conversion.  An ultraviolet light photon has higher energy than a visible light photon which has higher energy than an infrared photon.  

In the ultraviolet to infrared spectrum, energy levels go from 

• UVC - ultraviolet short wave - 250nm (highest energy level)
• UVB - ultraviolet medium wave - 300nm
• UVA - ultraviolet long wave - 370nm
• Visible light - blue (400nm) to red (700nm)
• Infrared - 700nm to 8000nm (lowest energy level)

Within this spectrum, UVC has the highest energy or shortest wavelength.  Infrared has the lowest energy or longest wavelength.

Up-Conversion is a very unusual phenomenon.  A counter-intuitive anti-stokes process occurs where the material absorbs lower energy photons and emits higher energy photons as fluorescence.  The trick is that up-conversion materials absorb two or more low energy photons and then emit one high energy photon.  By definition, up-conversion phosphors must be much less efficient than down-conversion phosphors.  Typically, up-conversion phosphors are illuminated with high intensity light sources such as lasers in a controlled (subdued) lighting environment.

Our IRP1 IR absorbing pigment does not fluoresce and has a low visibility in the human eye range.  The IRP1 looks like faint green talcum powder and can be applied to white paper leaving no visible trace.  With an IR sensitive camera, you can see the pigment.

We also have a large library of fluorescent materials not listed on our site.  Contact us if you have a particular need.