We have two classes of IR invisible marking products:
Our IR Fluorescent Items
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
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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