EM radiation consists of an electrical field that varies in magnitude in a direction perpendicular to the direction of propagation. Measured in meters or fractions of meters. There are no natural breaks in the em spectrum. These separations are made by us for our convenience. Micrometers C auses fluorescence and is good in some geological and vegetation applications.
Some flowers also fluoress under UV light allowing insects to locate nectar reservoirs.
N ot much is done with UV for remote sensing since these shorter wavelengths are easily scattered by the atmosphere making spaceborne and some airborne sensors impractical. For an excellent reading on the EM spectrum look at this site at the Jet Propulsion Laboratory.