Down-conversion refers to a material that absorbs energy at a higher level (lower wavelength) and emits energy at a lower level (longer wavelength). Most fluorescent materials operate this way. The typical longwave UV paints that glow in the visible when illuminated with a longwave UV or blacklight are down-conversion paints. The human eye naturally is not very sensitive to the UV light so we don't see the UV light well, but we do see where the paints glow in the visible well.
IR down-conversion materials convert visible or infrared light to another infrared frequency. We have two types of IR down-conversion materials.
Down conversion refers to a material that absorbs light at a higher energy (shorter wavelength) and emits light at a low energy wavelength (longer wavelength). Most materials that fluoresce will exhibit down conversion because the energy is flowing from a higher level to a lower level. To fluoresce, the material must absorb energy at one wavelength which temporarily bumps some of its electrons to a higher energy orbit. When the electrons fall back to their normal energy level, a photon is emitted which is the fluorescence.
We have many sorts of down conversion materials. We materials that have excitations:
Materials tend to be either organic or inorganic. Organic materials may have solubility such as our IR Ink #1 or #2 which have ethanol solubility, and inorganic materials which are very fine ceramic crystals with no solubility. Organic materials will fade in sunlight while the inorganic materials will not. We can make dispersions or suspensions of our inorganic materials into a type of paint.