Bombarding the surface of a material with some particle or radiation may produce the emission of electromagnetic radiation. This emission can be in the wide spectral range from ultraviolet up to infrared. This general phenomenon is known as luminescence.
The types of luminescence are generally distinguished by the type of incident radiation:
CL is similar to the photoluminescence (PL) technique, but the excitation of high energy electrons can produce all the transition to the higher energy excitation n states and induce light emission in the wide spectral range. The electron beam is typically produced in an electron microscope (SEM, TEM, or microprobe EPMA) or in a Cathodoluminescence microscopy coupled with electron gun (OM-CL).