Building a Filter-Wheel Apparatus to Generate Spectroscopic Information from Cathodoluminescence Images Obtained in a Scanning Electron Microscope: Applications in Zircon Geochronology

Abstract. We present a simple inexpensive design for a filter wheel to modify a broadband cathodoluminescence (CL) detector in a scanning electron microscope (SEM) to provide spectroscopic information along with image processing and visualization tools that enhances the quality and utility of that imagery. This system was initially tested using a ZnS standard known to produce a strong CL signal in the visible spectrum. Enhanced images and spectroscopic data could also be used for grain and spot targeting of natural zircons that commonly precedes isotopic analysis by laser ablation or ion microprobe. The filter-wheel system was made from inexpensive or 3D printed materials, allows for interchangeable filters for a variety of applications, and the switching between those filters without the user breaking SEM vacuum. The color filtered images were used to create color composite images similar to those generated by higher-end spectrometers with built-in color filtering capability. The embedded data from the RGB pixels of the color filtered images were then used to generate 2D and 3D graphs providing another visual path for comparing relative intensities. A color composite image and associated 3D graphs for a prototypical zircon sample was generated to demonstrate the usefulness of the device and utility of plots. Design documents and specifications for the color filter wheel, and codes to generate images and plots are available on https://weber.edu/cos/instrument_information.html.