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Up-Conversion
Down-Conversion

We have two classes of IR invisible marking products:

bulletIR Down-Conversion: Visible to IR, and IR to IR
bulletIR Up-Conversion:  IR to Visible (anti-stokes shift)

Our IR Fluorescent Items

  1. IR Ink writing pen:  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 ink.
  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 

bulletUVC - ultraviolet short wave - 250nm (highest energy level)
bulletUVB - ultraviolet medium wave - 300nm
bulletUVA - ultraviolet long wave - 370nm
bulletVisible light - blue (400nm) to red (700nm)
bulletInfrared - 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.

 

 

 

 

 

                                

 

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Last modified: February 18, 2013