How to Overcome Imaging Problems Associated with Carbonate Minerals on SEM-Based Cathodoluminescence Systems

On SEM-based cathodoluminescence systems (scanned CL), methods are needed to overcome image-quality problems caused by persistent luminescence of carbonate minerals. An effective solution to the persistence problem is to acquire images using only the shorter wavelengths, most easily done by using a broadband, short-wavelength (UV-blue range) filter. The filter used provides 80% to 90% transmissivity in the range of 385 to 495 nm and some transmissivity as low as 350 nm. The filter allows transmission of the relatively nonpersistent UV-violet luminescence present in most carbonates in the range of 350 to 425 nm, but blocks the common orange-red wavelength luminescence found in carbonates. The lack of imaging problems in subsequent images shows that persistent luminescence in carbonates is primarily in the orange-red wavelengths. Cathodoluminescence images produced using a short-wavelength filter are comparable in detail to those obtained from conventional light-microscope-based cathodoluminescence systems. In almost all examples, features visible in the orange-red wavelengths show corresponding variations in luminescence in the shorter wavelengths.