Cathodoluminescence (CL)

About this technique

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Cathodoluminescence (CL) is the non-incandescent emission of light (photons) from a luminescent material excited by an electron beam. CL photons (from ultraviolet, through visible to the near-infrared) are emitted as result of electronic transitions between the conduction and valence band and may also involve electronic transitions associated with defect levels within the band gap. The optical, electrical and mechanical properties of solids are dependent on the presence of microscopic defects (imperfections and impurities) and therefore CL microanalysis is a useful spectroscopy and imaging technique for characterising these properties with high sensitivity and spatial resolution.

Cathodoluminescence microanalysis in a scanning electron microscope (SEM) enables high-sensitivity detection of defect centers in a wide range of materials. CL image resolution can range from tens of nanometres to micrometres and is dependent on specimen configuration and interaction volume, carrier diffusion and electron beam parameters, etc. Quantitative CL microanalysis of defect and impurity concentrations is not generally achievable because of the lack of a general explanation for the complex nature of competitive recombination processes.

The preparation of a specimen for CL microanalysis in an SEM is similar to preparation for other SEM-based microanalytical techniques. Many luminescent specimens also need coating with a thin conductive film to minimise surface charging effects.