Cathodoluminescence (CL)

Cathodoluminescence (CL) is an optical and electrical phenomenon that occurs when an electron beam interacts with a luminescent material and results in the production of visible light. It is an imaging technique that can be applied to a wide range of applications including semiconductors, insulators, ceramics and a variety of naturally occurring mineral phases.

Typically CL is the result of structural defects within a crystal lattice or due to the presence/absence of trace elements within a mineral. In geological materials it can be a powerful tool to provide textural evidence on growth zonation, diagenesis, overgrowths/alteration and provenance.

The AAC operates two CL systems on the electron microscopes. The first is a monochromatic imaging system on the SEM. It uses a retractable mirror to direct light to a blue-sensitive bi-alkali photocathode (sensitive to light in the range of 310 to 650nm). This produces black and white images showing low to high CL response during normal beam scan acquisitions and is therefore a relatively rapid technique.

The second system is a discrete optical spectrometer attached to the EPMA (XCLent). Here light is captured via the internal optical microscope system and passed via fibre optic cable to a spectrometer (sensitive within the 300-1100nm range). Full spectrum data can be acquired either from discrete spots or during mapping (hyperspectral mapping).

Image below: CL image of synthetic zircons.