CL (Cathodoluminescence) is a technique that detects light emitted from a material when excited by an electron beam — the emitted photon energy, intensity, and spatial distribution reveal band gap, defects, composition, and stress at the nanoscale.

How Does CL Work?

• Excitation: The SEM/STEM electron beam creates electron-hole pairs in the sample.
• Recombination: Some carriers recombine radiatively, emitting photons with characteristic energies.
• Detection: A parabolic mirror + spectrometer collects and analyzes the emitted light.
• Modes: Panchromatic (total intensity), monochromatic (single wavelength), or spectral (full spectrum at each pixel).

Why It Matters

• Band Gap Mapping: Maps local band gap variations in semiconductors and quantum structures.
• Defect Identification: Non-radiative defects appear as dark spots (killed luminescence).
• Spatial Resolution: ~50-100 nm in SEM, sub-nm in STEM — orders of magnitude better than photoluminescence.

CL is making materials glow with electrons — using the electron beam to excite luminescence that reveals band structure, defects, and composition at the nanoscale.