When an electron beam interacts with a material, a multitude of processes occur which can be employed for various kinds of microscopy. Besides electron signals, a broad spectrum of electromagnetic radiation ranging from x-rays to the mid-IR is generated through a variety of incoherent and coherent processes.
The radiation that is generated in the ultraviolet/visible/near-infrared regime of the electromagnetic spectrum is referred to as cathodoluminescence (CL) as the radiation is generated by cathode rays (fast electrons). The electron beam causes the material to flouresce as it returns to a ground state.
Figure 1: Schematic of the processes that occur when an energetic beam of electrons impinges on a sample. These processes are used for different characterization techniques as indicated in the schematic. CL is the electromagnetic radiation in the UV/VIS/IR spectral range.